diff --git a/src/intervals_mcp_server/credentials.py b/src/intervals_mcp_server/credentials.py
index 58124c5..8f66acc 100644
--- a/src/intervals_mcp_server/credentials.py
+++ b/src/intervals_mcp_server/credentials.py
@@ -32,7 +32,10 @@ class CredentialError(Exception):
 
 async def resolve_caller_credentials() -> tuple[str, str]:
     """Return ``(athlete_id, api_key)`` for the current caller or raise CredentialError."""
-    token = get_access_token()
+    try:
+        token = get_access_token()
+    except Exception:  # noqa: BLE001 - no auth context (stdio/local dev)
+        token = None
     if token is not None and token.subject:
         creds = await store.get_active_credentials(token.subject)
         if creds is None:
diff --git a/src/intervals_mcp_server/tools/activities.py b/src/intervals_mcp_server/tools/activities.py
index 0fa5187..5a54af6 100644
--- a/src/intervals_mcp_server/tools/activities.py
+++ b/src/intervals_mcp_server/tools/activities.py
@@ -7,20 +7,19 @@ This module contains tools for retrieving and managing athlete activities.
 from datetime import datetime, timedelta
 from typing import Any
 
+from intervals_mcp_server import credentials
 from intervals_mcp_server.api.client import make_intervals_request
-from intervals_mcp_server.config import get_config
+from intervals_mcp_server.credentials import CredentialError
 from intervals_mcp_server.tools.gear import (
     resolve_gear_for_activity,
     resolve_gear_for_activities,
 )
 from intervals_mcp_server.utils.formatting import format_activity_message, format_activity_summary, format_intervals
-from intervals_mcp_server.utils.validation import resolve_athlete_id, resolve_date_params
+from intervals_mcp_server.utils.validation import resolve_date_params
 
 # Import mcp instance from shared module for tool registration
 from intervals_mcp_server.mcp_instance import mcp  # noqa: F401
 
-config = get_config()
-
 
 def _parse_activities_from_result(result: Any) -> list[dict[str, Any]]:
     """Extract a list of activity dictionaries from the API result."""
@@ -105,28 +104,24 @@ def _format_activities_response(
 
 
 @mcp.tool()
-async def get_activities(  # pylint: disable=too-many-arguments,too-many-return-statements,too-many-branches,too-many-positional-arguments
-    athlete_id: str | None = None,
-    api_key: str | None = None,
+async def get_activities(  # pylint: disable=too-many-return-statements,too-many-branches
     start_date: str | None = None,
     end_date: str | None = None,
     limit: int = 10,
     include_unnamed: bool = False,
 ) -> str:
-    """Get a list of activities for an athlete from Intervals.icu
+    """Get a list of activities for the signed-in athlete from Intervals.icu
 
     Args:
-        athlete_id: The Intervals.icu athlete ID (optional, will use ATHLETE_ID from .env if not provided)
-        api_key: The Intervals.icu API key (optional, will use API_KEY from .env if not provided)
         start_date: Start date in YYYY-MM-DD format (optional, defaults to 30 days ago)
         end_date: End date in YYYY-MM-DD format (optional, defaults to today)
         limit: Maximum number of activities to return (optional, defaults to 10)
         include_unnamed: Whether to include unnamed activities (optional, defaults to False)
     """
-    # Resolve athlete ID and date parameters
-    athlete_id_to_use, error_msg = resolve_athlete_id(athlete_id, config.athlete_id)
-    if error_msg:
-        return error_msg
+    try:
+        athlete_id_to_use, api_key = await credentials.resolve_caller_credentials()
+    except CredentialError as exc:
+        return str(exc)
 
     start_date, end_date = resolve_date_params(start_date, end_date)
 
@@ -176,13 +171,17 @@ async def get_activities(  # pylint: disable=too-many-arguments,too-many-return-
 
 
 @mcp.tool()
-async def get_activity_details(activity_id: str, api_key: str | None = None) -> str:
+async def get_activity_details(activity_id: str) -> str:
     """Get detailed information for a specific activity from Intervals.icu
 
     Args:
         activity_id: The Intervals.icu activity ID
-        api_key: The Intervals.icu API key (optional, will use API_KEY from .env if not provided)
     """
+    try:
+        athlete_id_to_use, api_key = await credentials.resolve_caller_credentials()
+    except CredentialError as exc:
+        return str(exc)
+
     # Call the Intervals.icu API
     result = await make_intervals_request(url=f"/activity/{activity_id}", api_key=api_key)
 
@@ -199,8 +198,8 @@ async def get_activity_details(activity_id: str, api_key: str | None = None) ->
     if not isinstance(activity_data, dict):
         return f"Invalid activity format for activity {activity_id}."
 
-    # Resolve gear name (uses configured athlete_id via ATHLETE_ID env var)
-    await resolve_gear_for_activity(activity_data, api_key=api_key)
+    # Resolve gear name for the signed-in athlete
+    await resolve_gear_for_activity(activity_data, athlete_id=athlete_id_to_use, api_key=api_key)
 
     # Return a more detailed view of the activity
     detailed_view = format_activity_summary(activity_data)
@@ -220,7 +219,7 @@ async def get_activity_details(activity_id: str, api_key: str | None = None) ->
 
 
 @mcp.tool()
-async def get_activity_intervals(activity_id: str, api_key: str | None = None) -> str:
+async def get_activity_intervals(activity_id: str) -> str:
     """Get interval data for a specific activity from Intervals.icu
 
     This endpoint returns detailed metrics for each interval in an activity, including power, heart rate,
@@ -228,8 +227,12 @@ async def get_activity_intervals(activity_id: str, api_key: str | None = None) -
 
     Args:
         activity_id: The Intervals.icu activity ID
-        api_key: The Intervals.icu API key (optional, will use API_KEY from .env if not provided)
     """
+    try:
+        _athlete_id, api_key = await credentials.resolve_caller_credentials()
+    except CredentialError as exc:
+        return str(exc)
+
     # Call the Intervals.icu API
     result = await make_intervals_request(url=f"/activity/{activity_id}/intervals", api_key=api_key)
 
@@ -254,7 +257,6 @@ async def get_activity_intervals(activity_id: str, api_key: str | None = None) -
 @mcp.tool()
 async def get_activity_streams(
     activity_id: str,
-    api_key: str | None = None,
     stream_types: str | None = None,
 ) -> str:
     """Get stream data for a specific activity from Intervals.icu
@@ -264,11 +266,15 @@ async def get_activity_streams(
 
     Args:
         activity_id: The Intervals.icu activity ID
-        api_key: The Intervals.icu API key (optional, will use API_KEY from .env if not provided)
         stream_types: Comma-separated list of stream types to retrieve (optional, defaults to all available types)
                      Available types: time, watts, heartrate, cadence, altitude, distance,
                      core_temperature, skin_temperature, velocity_smooth
     """
+    try:
+        _athlete_id, api_key = await credentials.resolve_caller_credentials()
+    except CredentialError as exc:
+        return str(exc)
+
     # Build query parameters
     params = {}
     if stream_types:
@@ -330,13 +336,17 @@ async def get_activity_streams(
 
 
 @mcp.tool()
-async def get_activity_messages(activity_id: str, api_key: str | None = None) -> str:
+async def get_activity_messages(activity_id: str) -> str:
     """Get messages (notes/comments) for a specific activity from Intervals.icu
 
     Args:
         activity_id: The Intervals.icu activity ID
-        api_key: The Intervals.icu API key (optional, will use API_KEY from .env if not provided)
     """
+    try:
+        _athlete_id, api_key = await credentials.resolve_caller_credentials()
+    except CredentialError as exc:
+        return str(exc)
+
     result = await make_intervals_request(
         url=f"/activity/{activity_id}/messages",
         api_key=api_key,
@@ -365,15 +375,18 @@ async def get_activity_messages(activity_id: str, api_key: str | None = None) ->
 async def add_activity_message(
     activity_id: str,
     content: str,
-    api_key: str | None = None,
 ) -> str:
     """Add a message (note/comment) to an activity on Intervals.icu
 
     Args:
         activity_id: The Intervals.icu activity ID
         content: The message text to add
-        api_key: The Intervals.icu API key (optional, will use API_KEY from .env if not provided)
     """
+    try:
+        _athlete_id, api_key = await credentials.resolve_caller_credentials()
+    except CredentialError as exc:
+        return str(exc)
+
     result = await make_intervals_request(
         url=f"/activity/{activity_id}/messages",
         api_key=api_key,
diff --git a/src/intervals_mcp_server/tools/custom_items.py b/src/intervals_mcp_server/tools/custom_items.py
index 172d41c..3ef49dd 100644
--- a/src/intervals_mcp_server/tools/custom_items.py
+++ b/src/intervals_mcp_server/tools/custom_items.py
@@ -7,31 +7,26 @@ This module contains tools for managing athlete custom items (charts, fields, zo
 import json
 from typing import Any
 
+from intervals_mcp_server import credentials
 from intervals_mcp_server.api.client import make_intervals_request
-from intervals_mcp_server.config import get_config
+from intervals_mcp_server.credentials import CredentialError
 from intervals_mcp_server.utils.formatting import format_custom_item_details
-from intervals_mcp_server.utils.validation import resolve_athlete_id
 
 # Import mcp instance from shared module for tool registration
 from intervals_mcp_server.mcp_instance import mcp  # noqa: F401
 
-config = get_config()
-
 
 @mcp.tool()
 async def get_custom_items(
-    athlete_id: str | None = None,
-    api_key: str | None = None,
 ) -> str:
     """Get custom items (charts, custom fields, zones, etc.) for an athlete from Intervals.icu
 
     Args:
-        athlete_id: The Intervals.icu athlete ID (optional, will use ATHLETE_ID from .env if not provided)
-        api_key: The Intervals.icu API key (optional, will use API_KEY from .env if not provided)
     """
-    athlete_id_to_use, error_msg = resolve_athlete_id(athlete_id, config.athlete_id)
-    if error_msg:
-        return error_msg
+    try:
+        athlete_id_to_use, api_key = await credentials.resolve_caller_credentials()
+    except CredentialError as exc:
+        return str(exc)
 
     result = await make_intervals_request(
         url=f"/athlete/{athlete_id_to_use}/custom-item", api_key=api_key
@@ -58,19 +53,16 @@ async def get_custom_items(
 @mcp.tool()
 async def get_custom_item_by_id(
     item_id: int,
-    athlete_id: str | None = None,
-    api_key: str | None = None,
 ) -> str:
     """Get detailed information for a specific custom item from Intervals.icu
 
     Args:
         item_id: The custom item ID
-        athlete_id: The Intervals.icu athlete ID (optional, will use ATHLETE_ID from .env if not provided)
-        api_key: The Intervals.icu API key (optional, will use API_KEY from .env if not provided)
     """
-    athlete_id_to_use, error_msg = resolve_athlete_id(athlete_id, config.athlete_id)
-    if error_msg:
-        return error_msg
+    try:
+        athlete_id_to_use, api_key = await credentials.resolve_caller_credentials()
+    except CredentialError as exc:
+        return str(exc)
 
     result = await make_intervals_request(
         url=f"/athlete/{athlete_id_to_use}/custom-item/{item_id}", api_key=api_key
@@ -89,8 +81,6 @@ async def get_custom_item_by_id(
 async def create_custom_item(
     name: str,
     item_type: str,
-    athlete_id: str | None = None,
-    api_key: str | None = None,
     description: str | None = None,
     content: dict[str, Any] | None = None,
     visibility: str | None = None,
@@ -100,17 +90,16 @@ async def create_custom_item(
     Args:
         name: Name of the custom item
         item_type: Type of custom item (e.g. FITNESS_CHART, TRACE_CHART, INPUT_FIELD, ACTIVITY_FIELD, INTERVAL_FIELD, ACTIVITY_STREAM, ACTIVITY_CHART, ACTIVITY_HISTOGRAM, ACTIVITY_HEATMAP, ACTIVITY_MAP, ACTIVITY_PANEL, ZONES)
-        athlete_id: The Intervals.icu athlete ID (optional, will use ATHLETE_ID from .env if not provided)
-        api_key: The Intervals.icu API key (optional, will use API_KEY from .env if not provided)
         description: Description of the custom item (optional)
         content: Configuration content for the custom item as a dict (optional). Important enum values:
             - "type" field for INPUT_FIELD/ACTIVITY_FIELD: must be "numeric", "text", or "select" (NOT "number")
             - "aggregate" field: must be "MIN", "SUM", "MAX", or "AVERAGE" (NOT "AVG")
         visibility: Visibility setting: PRIVATE, FOLLOWERS, or PUBLIC (optional)
     """
-    athlete_id_to_use, error_msg = resolve_athlete_id(athlete_id, config.athlete_id)
-    if error_msg:
-        return error_msg
+    try:
+        athlete_id_to_use, api_key = await credentials.resolve_caller_credentials()
+    except CredentialError as exc:
+        return str(exc)
 
     data: dict[str, Any] = {"name": name, "type": item_type}
     if description is not None:
@@ -144,8 +133,6 @@ async def create_custom_item(
 @mcp.tool()
 async def update_custom_item(
     item_id: int,
-    athlete_id: str | None = None,
-    api_key: str | None = None,
     name: str | None = None,
     item_type: str | None = None,
     description: str | None = None,
@@ -156,8 +143,6 @@ async def update_custom_item(
 
     Args:
         item_id: The custom item ID to update
-        athlete_id: The Intervals.icu athlete ID (optional, will use ATHLETE_ID from .env if not provided)
-        api_key: The Intervals.icu API key (optional, will use API_KEY from .env if not provided)
         name: New name for the custom item (optional)
         item_type: New type for the custom item (optional)
         description: New description for the custom item (optional)
@@ -166,9 +151,10 @@ async def update_custom_item(
             - "aggregate" field: must be "MIN", "SUM", "MAX", or "AVERAGE" (NOT "AVG")
         visibility: New visibility setting: PRIVATE, FOLLOWERS, or PUBLIC (optional)
     """
-    athlete_id_to_use, error_msg = resolve_athlete_id(athlete_id, config.athlete_id)
-    if error_msg:
-        return error_msg
+    try:
+        athlete_id_to_use, api_key = await credentials.resolve_caller_credentials()
+    except CredentialError as exc:
+        return str(exc)
 
     data: dict[str, Any] = {}
     if name is not None:
@@ -206,19 +192,16 @@ async def update_custom_item(
 @mcp.tool()
 async def delete_custom_item(
     item_id: int,
-    athlete_id: str | None = None,
-    api_key: str | None = None,
 ) -> str:
     """Delete a custom item for an athlete from Intervals.icu
 
     Args:
         item_id: The custom item ID to delete
-        athlete_id: The Intervals.icu athlete ID (optional, will use ATHLETE_ID from .env if not provided)
-        api_key: The Intervals.icu API key (optional, will use API_KEY from .env if not provided)
     """
-    athlete_id_to_use, error_msg = resolve_athlete_id(athlete_id, config.athlete_id)
-    if error_msg:
-        return error_msg
+    try:
+        athlete_id_to_use, api_key = await credentials.resolve_caller_credentials()
+    except CredentialError as exc:
+        return str(exc)
 
     result = await make_intervals_request(
         url=f"/athlete/{athlete_id_to_use}/custom-item/{item_id}",
diff --git a/src/intervals_mcp_server/tools/events.py b/src/intervals_mcp_server/tools/events.py
index 2ab93fe..94bdb5e 100644
--- a/src/intervals_mcp_server/tools/events.py
+++ b/src/intervals_mcp_server/tools/events.py
@@ -8,18 +8,17 @@ import json
 from datetime import datetime
 from typing import Any
 
+from intervals_mcp_server import credentials
 from intervals_mcp_server.api.client import make_intervals_request
-from intervals_mcp_server.config import get_config
+from intervals_mcp_server.credentials import CredentialError
 from intervals_mcp_server.utils.dates import get_default_end_date, get_default_future_end_date
 from intervals_mcp_server.utils.formatting import format_event_details, format_event_summary
 from intervals_mcp_server.utils.types import WorkoutDoc
-from intervals_mcp_server.utils.validation import resolve_activity_type, resolve_athlete_id, validate_date
+from intervals_mcp_server.utils.validation import resolve_activity_type, validate_date
 
 # Import mcp instance from shared module for tool registration
 from intervals_mcp_server.mcp_instance import mcp  # noqa: F401
 
-config = get_config()
-
 
 def _prepare_event_data(  # pylint: disable=too-many-arguments,too-many-positional-arguments
     name: str,
@@ -89,23 +88,20 @@ async def _delete_events_list(
 
 @mcp.tool()
 async def get_events(
-    athlete_id: str | None = None,
-    api_key: str | None = None,
     start_date: str | None = None,
     end_date: str | None = None,
 ) -> str:
     """Get events for an athlete from Intervals.icu
 
     Args:
-        athlete_id: The Intervals.icu athlete ID (optional, will use ATHLETE_ID from .env if not provided)
-        api_key: The Intervals.icu API key (optional, will use API_KEY from .env if not provided)
         start_date: Start date in YYYY-MM-DD format (optional, defaults to today)
         end_date: End date in YYYY-MM-DD format (optional, defaults to 30 days from today)
     """
     # Resolve athlete ID
-    athlete_id_to_use, error_msg = resolve_athlete_id(athlete_id, config.athlete_id)
-    if error_msg:
-        return error_msg
+    try:
+        athlete_id_to_use, api_key = await credentials.resolve_caller_credentials()
+    except CredentialError as exc:
+        return str(exc)
 
     # Parse date parameters (events use different defaults)
     if not start_date:
@@ -147,20 +143,17 @@ async def get_events(
 @mcp.tool()
 async def get_event_by_id(
     event_id: str,
-    athlete_id: str | None = None,
-    api_key: str | None = None,
 ) -> str:
     """Get detailed information for a specific event from Intervals.icu
 
     Args:
         event_id: The Intervals.icu event ID
-        athlete_id: The Intervals.icu athlete ID (optional, will use ATHLETE_ID from .env if not provided)
-        api_key: The Intervals.icu API key (optional, will use API_KEY from .env if not provided)
     """
     # Resolve athlete ID
-    athlete_id_to_use, error_msg = resolve_athlete_id(athlete_id, config.athlete_id)
-    if error_msg:
-        return error_msg
+    try:
+        athlete_id_to_use, api_key = await credentials.resolve_caller_credentials()
+    except CredentialError as exc:
+        return str(exc)
 
     # Call the Intervals.icu API
     result = await make_intervals_request(
@@ -184,18 +177,15 @@ async def get_event_by_id(
 @mcp.tool()
 async def delete_event(
     event_id: str,
-    athlete_id: str | None = None,
-    api_key: str | None = None,
 ) -> str:
     """Delete event for an athlete from Intervals.icu
     Args:
-        athlete_id: The Intervals.icu athlete ID (optional, will use ATHLETE_ID from .env if not provided)
-        api_key: The Intervals.icu API key (optional, will use API_KEY from .env if not provided)
         event_id: The Intervals.icu event ID
     """
-    athlete_id_to_use, error_msg = resolve_athlete_id(athlete_id, config.athlete_id)
-    if error_msg:
-        return error_msg
+    try:
+        athlete_id_to_use, api_key = await credentials.resolve_caller_credentials()
+    except CredentialError as exc:
+        return str(exc)
     if not event_id:
         return "Error: No event ID provided."
     result = await make_intervals_request(
@@ -234,20 +224,17 @@ async def _fetch_events_for_deletion(
 async def delete_events_by_date_range(
     start_date: str,
     end_date: str,
-    athlete_id: str | None = None,
-    api_key: str | None = None,
 ) -> str:
     """Delete events for an athlete from Intervals.icu in the specified date range.
 
     Args:
-        athlete_id: The Intervals.icu athlete ID (optional, will use ATHLETE_ID from .env if not provided)
-        api_key: The Intervals.icu API key (optional, will use API_KEY from .env if not provided)
         start_date: Start date in YYYY-MM-DD format
         end_date: End date in YYYY-MM-DD format
     """
-    athlete_id_to_use, error_msg = resolve_athlete_id(athlete_id, config.athlete_id)
-    if error_msg:
-        return error_msg
+    try:
+        athlete_id_to_use, api_key = await credentials.resolve_caller_credentials()
+    except CredentialError as exc:
+        return str(exc)
 
     events, error_msg = await _fetch_events_for_deletion(
         athlete_id_to_use, api_key, start_date, end_date
@@ -264,8 +251,6 @@ async def delete_events_by_date_range(
 async def add_or_update_event(  # pylint: disable=too-many-arguments,too-many-positional-arguments
     workout_type: str,
     name: str,
-    athlete_id: str | None = None,
-    api_key: str | None = None,
     event_id: str | None = None,
     start_date: str | None = None,
     workout_doc: WorkoutDoc | None = None,
@@ -278,8 +263,6 @@ async def add_or_update_event(  # pylint: disable=too-many-arguments,too-many-po
     Many arguments are required as this MCP tool function maps directly to the Intervals.icu API parameters.
 
     Args:
-        athlete_id: The Intervals.icu athlete ID (optional, will use ATHLETE_ID from .env if not provided)
-        api_key: The Intervals.icu API key (optional, will use API_KEY from .env if not provided)
         event_id: The Intervals.icu event ID (optional, will use event_id from .env if not provided)
         start_date: Start date in YYYY-MM-DD format (optional, defaults to today)
         name: Name of the activity
@@ -337,9 +320,10 @@ async def add_or_update_event(  # pylint: disable=too-many-arguments,too-many-po
     - Use "reps" with nested steps to define repeat intervals (as in example above)
     - Define one of "power", "hr" or "pace" to define step intensity
     """
-    athlete_id_to_use, error_msg = resolve_athlete_id(athlete_id, config.athlete_id)
-    if error_msg:
-        return error_msg
+    try:
+        athlete_id_to_use, api_key = await credentials.resolve_caller_credentials()
+    except CredentialError as exc:
+        return str(exc)
 
     if not start_date:
         start_date = datetime.now().strftime("%Y-%m-%d")
@@ -362,8 +346,6 @@ async def add_or_update_note(
     description: str,
     start_date: str | None = None,
     color: str | None = "green",
-    athlete_id: str | None = None,
-    api_key: str | None = None,
     event_id: str | None = None,
 ) -> str:
     """Add or update a plain text note (category NOTE) on the Intervals.icu calendar.
@@ -377,9 +359,10 @@ async def add_or_update_note(
         api_key: The Intervals.icu API key (optional)
         event_id: The Intervals.icu event ID (optional, for updates)
     """
-    athlete_id_to_use, error_msg = resolve_athlete_id(athlete_id, config.athlete_id)
-    if error_msg:
-        return error_msg
+    try:
+        athlete_id_to_use, api_key = await credentials.resolve_caller_credentials()
+    except CredentialError as exc:
+        return str(exc)
 
     if not start_date:
         start_date = datetime.now().strftime("%Y-%m-%d")
diff --git a/src/intervals_mcp_server/tools/gear.py b/src/intervals_mcp_server/tools/gear.py
index adddde4..5816209 100644
--- a/src/intervals_mcp_server/tools/gear.py
+++ b/src/intervals_mcp_server/tools/gear.py
@@ -19,8 +19,10 @@ Call `get_gear_list(refresh=True)` to bust the cache.
 
 from typing import Any
 
+from intervals_mcp_server import credentials
 from intervals_mcp_server.api.client import make_intervals_request
 from intervals_mcp_server.config import get_config
+from intervals_mcp_server.credentials import CredentialError
 from intervals_mcp_server.utils.validation import resolve_athlete_id
 
 # Import mcp instance from shared module for tool registration
@@ -151,26 +153,21 @@ async def resolve_gear_for_activities(
 
 @mcp.tool()
 async def get_gear_list(
-    athlete_id: str | None = None,
-    api_key: str | None = None,
     refresh: bool = False,
 ) -> str:
-    """Get the gear catalog (bikes, shoes, etc.) for an athlete from Intervals.icu.
+    """Get the gear catalog (bikes, shoes, etc.) for the signed-in athlete from Intervals.icu.
 
     Returns one line per gear item with id, type, name, and basic stats.
     The result is cached for the MCP process lifetime; pass refresh=True to
     re-fetch.
 
     Args:
-        athlete_id: The Intervals.icu athlete ID (optional, will use ATHLETE_ID from .env if not provided)
-        api_key: The Intervals.icu API key (optional, will use API_KEY from .env if not provided)
         refresh: If True, bypass the cache and re-fetch from the API (default False)
     """
-    athlete_id_to_use, error_msg = resolve_athlete_id(athlete_id, config.athlete_id)
-    if error_msg:
-        return error_msg
-    if not athlete_id_to_use:
-        return "Error: athlete_id is required (either as argument or via ATHLETE_ID env var)."
+    try:
+        athlete_id_to_use, api_key = await credentials.resolve_caller_credentials()
+    except CredentialError as exc:
+        return str(exc)
 
     # Single fetch path: get_gear_raw consults the cache and only hits the API
     # on a cold cache or when refresh=True.
diff --git a/src/intervals_mcp_server/tools/power_curves.py b/src/intervals_mcp_server/tools/power_curves.py
index c3ea268..14dcd21 100644
--- a/src/intervals_mcp_server/tools/power_curves.py
+++ b/src/intervals_mcp_server/tools/power_curves.py
@@ -8,16 +8,14 @@ import json
 from datetime import datetime
 from typing import Any
 
+from intervals_mcp_server import credentials
 from intervals_mcp_server.api.client import make_intervals_request
-from intervals_mcp_server.config import get_config
+from intervals_mcp_server.credentials import CredentialError
 from intervals_mcp_server.utils.formatting import format_power_curves
-from intervals_mcp_server.utils.validation import resolve_activity_type, resolve_athlete_id
 
 # Import mcp instance from shared module for tool registration
 from intervals_mcp_server.mcp_instance import mcp  # noqa: F401
 
-config = get_config()
-
 # 5s, 15s, 30s, 1min, 2min, 5min, 10min, 20min, 60min
 DEFAULT_DURATIONS: tuple[int, ...] = (5, 15, 30, 60, 120, 300, 600, 1200, 3600)
 
@@ -135,8 +133,6 @@ async def get_athlete_power_curves(
     this_season: bool = True,
     last_season: bool = True,
     include_normalised: bool = True,
-    athlete_id: str | None = None,
-    api_key: str | None = None,
 ) -> str:
     """Get power curves for an athlete from Intervals.icu.
 
@@ -152,15 +148,14 @@ async def get_athlete_power_curves(
         this_season: Include this season's curve (default True)
         last_season: Include last season's curve (default True)
         include_normalised: Include weight-normalised W/kg values (default True)
-        athlete_id: Intervals.icu athlete ID (optional, uses ATHLETE_ID from .env if not provided)
-        api_key: Optional API key override. Uses API_KEY from .env if not provided.
     """
     if durations is None:
         durations = list(DEFAULT_DURATIONS)
 
-    athlete_id_to_use, error_msg = resolve_athlete_id(athlete_id, config.athlete_id)
-    if error_msg:
-        return error_msg
+    try:
+        athlete_id_to_use, api_key = await credentials.resolve_caller_credentials()
+    except CredentialError as exc:
+        return str(exc)
 
     if indoor_outdoor and indoor_outdoor not in ("indoor", "outdoor"):
         return "Error: indoor_outdoor must be 'indoor', 'outdoor', or omitted."
diff --git a/src/intervals_mcp_server/tools/wellness.py b/src/intervals_mcp_server/tools/wellness.py
index 5ff5285..df99338 100644
--- a/src/intervals_mcp_server/tools/wellness.py
+++ b/src/intervals_mcp_server/tools/wellness.py
@@ -4,41 +4,37 @@ Wellness-related MCP tools for Intervals.icu.
 This module contains tools for retrieving athlete wellness data.
 """
 
+from intervals_mcp_server import credentials
 from intervals_mcp_server.api.client import make_intervals_request
-from intervals_mcp_server.config import get_config
+from intervals_mcp_server.credentials import CredentialError
 from intervals_mcp_server.utils.formatting import format_wellness_entry
-from intervals_mcp_server.utils.validation import resolve_athlete_id, resolve_date_params
+from intervals_mcp_server.utils.validation import resolve_date_params
 
 # Import mcp instance from shared module for tool registration
 from intervals_mcp_server.mcp_instance import mcp  # noqa: F401
 
-config = get_config()
-
 
 @mcp.tool()
 async def get_wellness_data(
-    athlete_id: str | None = None,
-    api_key: str | None = None,
     start_date: str | None = None,
     end_date: str | None = None,
     include_all_fields: bool = False,
 ) -> str:
-    """Get wellness data for an athlete from Intervals.icu.
+    """Get wellness data for the signed-in athlete from Intervals.icu.
 
     By default returns standard wellness fields (training metrics, vitals, sleep,
     subjective scores, etc.). Set include_all_fields=True to also include any
     additional or custom fields configured by the user in Intervals.icu.
 
     Args:
-        athlete_id: The Intervals.icu athlete ID (optional, will use ATHLETE_ID from .env if not provided)
-        api_key: The Intervals.icu API key (optional, will use API_KEY from .env if not provided)
         start_date: Start date in YYYY-MM-DD format (optional, defaults to 30 days ago)
         end_date: End date in YYYY-MM-DD format (optional, defaults to today)
         include_all_fields: If True, include additional and custom fields beyond the standard set (optional, defaults to False)
     """
-    athlete_id_to_use, error_msg = resolve_athlete_id(athlete_id, config.athlete_id)
-    if error_msg:
-        return error_msg
+    try:
+        athlete_id_to_use, api_key = await credentials.resolve_caller_credentials()
+    except CredentialError as exc:
+        return str(exc)
 
     start_date, end_date = resolve_date_params(start_date, end_date)
 
diff --git a/tests/conftest.py b/tests/conftest.py
new file mode 100644
index 0000000..0cea35e
--- /dev/null
+++ b/tests/conftest.py
@@ -0,0 +1,22 @@
+"""Shared test fixtures."""
+
+import pytest
+
+from intervals_mcp_server import credentials
+
+
+@pytest.fixture(autouse=True)
+def _default_caller_credentials(monkeypatch):
+    """Run tool tests as an enabled user with fixed credentials.
+
+    Tools resolve the caller via ``credentials.resolve_caller_credentials()``;
+    patching the module attribute covers every tool at once. A test can override
+    this (e.g. patch it to raise ``CredentialError``) to exercise the not-approved
+    path. Tests that exercise the resolver itself import the function directly and
+    are unaffected.
+    """
+
+    async def _creds():
+        return ("i1", "testkey")
+
+    monkeypatch.setattr(credentials, "resolve_caller_credentials", _creds)
diff --git a/tests/test_activities.py b/tests/test_activities.py
index a02935a..5bd0fbd 100644
--- a/tests/test_activities.py
+++ b/tests/test_activities.py
@@ -75,7 +75,7 @@ def test_format_response_empty_named_hint():
 # --------------------------------------------------------------------------- #
 def test_get_activities_error(monkeypatch):
     _patch_request(monkeypatch, lambda _n, _k: {"error": True, "message": "rate limited"})
-    out = asyncio.run(activities.get_activities(athlete_id="i1"))
+    out = asyncio.run(activities.get_activities())
     assert "Error fetching activities: rate limited" in out
 
 
@@ -87,7 +87,7 @@ def test_get_activities_requests_triple_limit_and_filters(monkeypatch):
 
     calls = _patch_request(monkeypatch, handler)
     out = asyncio.run(
-        activities.get_activities(athlete_id="i1", start_date="2026-06-01", end_date="2026-06-30", limit=5)
+        activities.get_activities(start_date="2026-06-01", end_date="2026-06-30", limit=5)
     )
     assert calls[0]["params"]["limit"] == 15  # limit * 3 when filtering unnamed
     assert len(calls) == 2  # topped up because named < limit
@@ -97,7 +97,7 @@ def test_get_activities_requests_triple_limit_and_filters(monkeypatch):
 
 def test_get_activities_include_unnamed_no_topup(monkeypatch):
     calls = _patch_request(monkeypatch, lambda _n, _k: [{"name": "Unnamed", "id": 1, "distance": 5}])
-    out = asyncio.run(activities.get_activities(athlete_id="i1", include_unnamed=True, limit=10))
+    out = asyncio.run(activities.get_activities(include_unnamed=True, limit=10))
     assert calls[0]["params"]["limit"] == 10  # no *3
     assert len(calls) == 1  # no fetch-more
     assert "Activities:" in out
diff --git a/tests/test_credentials.py b/tests/test_credentials.py
index 1765fac..3d2768b 100644
--- a/tests/test_credentials.py
+++ b/tests/test_credentials.py
@@ -51,6 +51,20 @@ def test_no_token_falls_back_to_env_config(monkeypatch):
     assert asyncio.run(resolve_caller_credentials()) == ("i999", "envkey")
 
 
+def test_get_access_token_raising_is_treated_as_no_context(monkeypatch):
+    # outside a request the SDK accessor may raise; that must fall back to env config
+    def _boom():
+        raise RuntimeError("no request context")
+
+    monkeypatch.setattr(credentials, "get_access_token", _boom)
+    monkeypatch.setattr(
+        credentials,
+        "get_config",
+        lambda: Config(api_key="envkey", athlete_id="i999", intervals_api_base_url="x", user_agent="t"),
+    )
+    assert asyncio.run(resolve_caller_credentials()) == ("i999", "envkey")
+
+
 def test_no_token_no_env_raises(monkeypatch):
     monkeypatch.setattr(credentials, "get_access_token", lambda: None)
     monkeypatch.setattr(
diff --git a/tests/test_custom_items.py b/tests/test_custom_items.py
index 2222977..48a07a4 100644
--- a/tests/test_custom_items.py
+++ b/tests/test_custom_items.py
@@ -38,19 +38,19 @@ def _run(coro):
 # --------------------------------------------------------------------------- #
 def test_get_custom_items_lists(monkeypatch):
     _patch(monkeypatch, lambda _k: [{"id": 1, "name": "Zones", "type": "ZONES", "description": "d"}])
-    out = _run(custom_items.get_custom_items(athlete_id="i1"))
+    out = _run(custom_items.get_custom_items())
     assert "Custom Items:" in out
     assert "ID: 1" in out and "Name: Zones" in out and "Type: ZONES" in out
 
 
 def test_get_custom_items_error(monkeypatch):
     _patch(monkeypatch, lambda _k: {"error": True, "message": "boom"})
-    assert "Error fetching custom items: boom" in _run(custom_items.get_custom_items(athlete_id="i1"))
+    assert "Error fetching custom items: boom" in _run(custom_items.get_custom_items())
 
 
 def test_get_custom_item_by_id_not_found(monkeypatch):
     _patch(monkeypatch, lambda _k: [])  # falsy / not a dict
-    assert "No custom item found with ID 7" in _run(custom_items.get_custom_item_by_id(7, athlete_id="i1"))
+    assert "No custom item found with ID 7" in _run(custom_items.get_custom_item_by_id(7))
 
 
 # --------------------------------------------------------------------------- #
@@ -60,7 +60,7 @@ def test_create_builds_full_payload(monkeypatch):
     rec = _patch(monkeypatch, lambda _k: {"id": 9, "name": "Chart", "type": "FITNESS_CHART"})
     out = _run(
         custom_items.create_custom_item(
-            name="Chart", item_type="FITNESS_CHART", athlete_id="i1",
+            name="Chart", item_type="FITNESS_CHART", 
             description="desc", content={"a": 1}, visibility="PRIVATE",
         )
     )
@@ -78,7 +78,7 @@ def test_create_parses_json_string_content(monkeypatch):
     rec = _patch(monkeypatch, lambda _k: {"id": 1, "name": "X", "type": "ZONES"})
     _run(
         custom_items.create_custom_item(
-            name="X", item_type="ZONES", athlete_id="i1", content='{"expression": "icu_training_load"}'
+            name="X", item_type="ZONES", content='{"expression": "icu_training_load"}'
         )
     )
     assert rec.calls[0]["data"]["content"] == {"expression": "icu_training_load"}  # parsed to dict
@@ -87,7 +87,7 @@ def test_create_parses_json_string_content(monkeypatch):
 def test_create_rejects_invalid_json_string(monkeypatch):
     rec = _patch(monkeypatch, lambda _k: {"id": 1})
     out = _run(
-        custom_items.create_custom_item(name="X", item_type="ZONES", athlete_id="i1", content="{not json")
+        custom_items.create_custom_item(name="X", item_type="ZONES", content="{not json")
     )
     assert "content must be valid JSON" in out
     assert rec.calls == []  # bailed before any request
@@ -95,7 +95,7 @@ def test_create_rejects_invalid_json_string(monkeypatch):
 
 def test_create_error_surfaced(monkeypatch):
     _patch(monkeypatch, lambda _k: {"error": True, "message": "bad type"})
-    out = _run(custom_items.create_custom_item(name="X", item_type="NOPE", athlete_id="i1"))
+    out = _run(custom_items.create_custom_item(name="X", item_type="NOPE"))
     assert "Error creating custom item: bad type" in out
 
 
@@ -104,7 +104,7 @@ def test_create_error_surfaced(monkeypatch):
 # --------------------------------------------------------------------------- #
 def test_update_sends_only_provided_fields_via_put(monkeypatch):
     rec = _patch(monkeypatch, lambda _k: {"id": 5, "name": "New", "type": "ZONES"})
-    _run(custom_items.update_custom_item(item_id=5, athlete_id="i1", name="New"))
+    _run(custom_items.update_custom_item(item_id=5, name="New"))
     call = rec.calls[0]
     assert call["method"] == "PUT"
     assert call["url"] == "/athlete/i1/custom-item/5"
@@ -113,7 +113,7 @@ def test_update_sends_only_provided_fields_via_put(monkeypatch):
 
 def test_update_invalid_json_string(monkeypatch):
     rec = _patch(monkeypatch, lambda _k: {"id": 5})
-    out = _run(custom_items.update_custom_item(item_id=5, athlete_id="i1", content="{bad"))
+    out = _run(custom_items.update_custom_item(item_id=5, content="{bad"))
     assert "content must be valid JSON" in out
     assert rec.calls == []
 
@@ -123,7 +123,7 @@ def test_update_invalid_json_string(monkeypatch):
 # --------------------------------------------------------------------------- #
 def test_delete_uses_delete_method(monkeypatch):
     rec = _patch(monkeypatch, lambda _k: {})
-    out = _run(custom_items.delete_custom_item(item_id=3, athlete_id="i1"))
+    out = _run(custom_items.delete_custom_item(item_id=3))
     call = rec.calls[0]
     assert call["method"] == "DELETE"
     assert call["url"] == "/athlete/i1/custom-item/3"
@@ -132,4 +132,4 @@ def test_delete_uses_delete_method(monkeypatch):
 
 def test_delete_error(monkeypatch):
     _patch(monkeypatch, lambda _k: {"error": True, "message": "locked"})
-    assert "Error deleting custom item: locked" in _run(custom_items.delete_custom_item(item_id=3, athlete_id="i1"))
+    assert "Error deleting custom item: locked" in _run(custom_items.delete_custom_item(item_id=3))
diff --git a/tests/test_events.py b/tests/test_events.py
index bb11428..f9715b2 100644
--- a/tests/test_events.py
+++ b/tests/test_events.py
@@ -74,7 +74,7 @@ def test_handle_event_response_branches(result, action, needle):
 # --------------------------------------------------------------------------- #
 def test_get_events_sends_date_params_and_formats(monkeypatch):
     rec = _patch(monkeypatch, lambda _k: [{"start_date_local": "2026-07-10", "id": "e1", "name": "Race", "race": True}])
-    out = _run(events.get_events(athlete_id="i1", start_date="2026-07-01", end_date="2026-07-31"))
+    out = _run(events.get_events(start_date="2026-07-01", end_date="2026-07-31"))
     call = rec.calls[0]
     assert call["url"] == "/athlete/i1/events"
     assert call["params"] == {"oldest": "2026-07-01", "newest": "2026-07-31"}
@@ -83,25 +83,25 @@ def test_get_events_sends_date_params_and_formats(monkeypatch):
 
 def test_get_events_error_surfaced(monkeypatch):
     _patch(monkeypatch, lambda _k: {"error": True, "message": "rate limited"})
-    out = _run(events.get_events(athlete_id="i1"))
+    out = _run(events.get_events())
     assert "Error fetching events: rate limited" in out
 
 
 def test_get_events_empty(monkeypatch):
     _patch(monkeypatch, lambda _k: [])
-    out = _run(events.get_events(athlete_id="i1"))
+    out = _run(events.get_events())
     assert "No events found" in out
 
 
 def test_get_event_by_id_invalid_format(monkeypatch):
     _patch(monkeypatch, lambda _k: [1, 2, 3])  # list, not a dict
-    out = _run(events.get_event_by_id("e1", athlete_id="i1"))
+    out = _run(events.get_event_by_id("e1"))
     assert "Invalid event format" in out
 
 
 def test_get_event_by_id_error(monkeypatch):
     _patch(monkeypatch, lambda _k: {"error": True, "message": "nope"})
-    out = _run(events.get_event_by_id("e1", athlete_id="i1"))
+    out = _run(events.get_event_by_id("e1"))
     assert "Error fetching event details: nope" in out
 
 
@@ -112,7 +112,7 @@ def test_add_event_posts_when_no_event_id(monkeypatch):
     rec = _patch(monkeypatch, lambda _k: {"id": "e99"})
     out = _run(
         events.add_or_update_event(
-            workout_type="Ride", name="Threshold", athlete_id="i1",
+            workout_type="Ride", name="Threshold", 
             start_date="2026-07-10", moving_time=3600, distance=40000,
             workout_doc=WorkoutDoc(description="d", steps=[Step(duration=600)]),
         )
@@ -128,7 +128,7 @@ def test_update_event_puts_when_event_id(monkeypatch):
     rec = _patch(monkeypatch, lambda _k: {"id": "e5"})
     _run(
         events.add_or_update_event(
-            workout_type="Ride", name="Threshold", athlete_id="i1",
+            workout_type="Ride", name="Threshold", 
             event_id="e5", start_date="2026-07-10",
         )
     )
@@ -139,13 +139,13 @@ def test_update_event_puts_when_event_id(monkeypatch):
 
 def test_add_event_invalid_date_returns_error(monkeypatch):
     _patch(monkeypatch, lambda _k: {"id": "e1"})
-    out = _run(events.add_or_update_event(workout_type="Ride", name="X", athlete_id="i1", start_date="07/10/2026"))
+    out = _run(events.add_or_update_event(workout_type="Ride", name="X", start_date="07/10/2026"))
     assert out.startswith("Error:")
 
 
 def test_add_note_uses_note_category_and_color(monkeypatch):
     rec = _patch(monkeypatch, lambda _k: {"id": "n1"})
-    _run(events.add_or_update_note(name="Sick day", description="rest", athlete_id="i1", start_date="2026-07-10", color="red"))
+    _run(events.add_or_update_note(name="Sick day", description="rest", start_date="2026-07-10", color="red"))
     data = rec.calls[0]["data"]
     assert data["category"] == "NOTE"
     assert data["color"] == "red"
@@ -157,13 +157,13 @@ def test_add_note_uses_note_category_and_color(monkeypatch):
 # --------------------------------------------------------------------------- #
 def test_delete_event_requires_id(monkeypatch):
     _patch(monkeypatch, lambda _k: {})
-    out = _run(events.delete_event("", athlete_id="i1"))
+    out = _run(events.delete_event(""))
     assert "No event ID provided" in out
 
 
 def test_delete_event_uses_delete_method(monkeypatch):
     rec = _patch(monkeypatch, lambda _k: {"deleted": True})
-    _run(events.delete_event("e7", athlete_id="i1"))
+    _run(events.delete_event("e7"))
     call = rec.calls[0]
     assert call["method"] == "DELETE"
     assert call["url"] == "/athlete/i1/events/e7"
@@ -176,12 +176,12 @@ def test_delete_by_range_counts_successes_and_failures(monkeypatch):
         return [{"id": 1}, {"id": 2}]  # the GET listing
 
     _patch(monkeypatch, handler)
-    out = _run(events.delete_events_by_date_range("2026-07-01", "2026-07-31", athlete_id="i1"))
+    out = _run(events.delete_events_by_date_range("2026-07-01", "2026-07-31"))
     assert "Deleted 1 events" in out
     assert "Failed to delete 1 events: [2]" in out
 
 
 def test_delete_by_range_fetch_error(monkeypatch):
     _patch(monkeypatch, lambda _k: {"error": True, "message": "boom"})
-    out = _run(events.delete_events_by_date_range("2026-07-01", "2026-07-31", athlete_id="i1"))
+    out = _run(events.delete_events_by_date_range("2026-07-01", "2026-07-31"))
     assert "Error deleting events: boom" in out
diff --git a/tests/test_server.py b/tests/test_server.py
index 8cfb6e9..50ffb9c 100644
--- a/tests/test_server.py
+++ b/tests/test_server.py
@@ -74,7 +74,7 @@ def test_get_activities(monkeypatch):
     monkeypatch.setattr(
         "intervals_mcp_server.tools.activities.make_intervals_request", fake_request
     )
-    result = asyncio.run(get_activities(athlete_id="1", limit=1, include_unnamed=True))
+    result = asyncio.run(get_activities(limit=1, include_unnamed=True))
     assert "Morning Ride" in result
     assert "Activities:" in result
 
@@ -122,7 +122,7 @@ def test_get_events(monkeypatch):
     # Patch in both api.client and tools modules to ensure it works
     monkeypatch.setattr("intervals_mcp_server.api.client.make_intervals_request", fake_request)
     monkeypatch.setattr("intervals_mcp_server.tools.events.make_intervals_request", fake_request)
-    result = asyncio.run(get_events(athlete_id="1", start_date="2024-01-01", end_date="2024-01-02"))
+    result = asyncio.run(get_events(start_date="2024-01-01", end_date="2024-01-02"))
     assert "Test Event" in result
     assert "Events:" in result
 
@@ -145,7 +145,7 @@ def test_get_event_by_id(monkeypatch):
     # Patch in both api.client and tools modules to ensure it works
     monkeypatch.setattr("intervals_mcp_server.api.client.make_intervals_request", fake_request)
     monkeypatch.setattr("intervals_mcp_server.tools.events.make_intervals_request", fake_request)
-    result = asyncio.run(get_event_by_id("e1", athlete_id="1"))
+    result = asyncio.run(get_event_by_id("e1"))
     assert "Event Details:" in result
     assert "Test Event" in result
 
@@ -168,7 +168,7 @@ def test_get_wellness_data(monkeypatch):
     # Patch in both api.client and tools modules to ensure it works
     monkeypatch.setattr("intervals_mcp_server.api.client.make_intervals_request", fake_request)
     monkeypatch.setattr("intervals_mcp_server.tools.wellness.make_intervals_request", fake_request)
-    result = asyncio.run(get_wellness_data(athlete_id="1"))
+    result = asyncio.run(get_wellness_data())
     assert "Wellness Data:" in result
     assert "2024-01-01" in result
 
@@ -193,7 +193,7 @@ def test_get_wellness_data_renders_macros(monkeypatch):
 
     monkeypatch.setattr("intervals_mcp_server.api.client.make_intervals_request", fake_request)
     monkeypatch.setattr("intervals_mcp_server.tools.wellness.make_intervals_request", fake_request)
-    result = asyncio.run(get_wellness_data(athlete_id="1"))
+    result = asyncio.run(get_wellness_data())
     assert "Wellness Data:" in result
     assert "2026-04-08" in result
     assert "Nutrition & Hydration:" in result
@@ -220,7 +220,7 @@ def test_get_wellness_data_include_all_fields(monkeypatch):
 
     monkeypatch.setattr("intervals_mcp_server.api.client.make_intervals_request", fake_request)
     monkeypatch.setattr("intervals_mcp_server.tools.wellness.make_intervals_request", fake_request)
-    result = asyncio.run(get_wellness_data(athlete_id="1", include_all_fields=True))
+    result = asyncio.run(get_wellness_data(include_all_fields=True))
     assert "Wellness Data:" in result
     assert "2024-01-01" in result
     assert "Fitness (CTL): 75" in result
@@ -321,7 +321,7 @@ def test_add_or_update_event(monkeypatch):
     )
     result = asyncio.run(
         add_or_update_event(
-            athlete_id="i1", start_date="2024-01-15", name="Test Workout", workout_type="Ride"
+            start_date="2024-01-15", name="Test Workout", workout_type="Ride"
         )
     )
     assert "Successfully created event id:" in result
@@ -465,7 +465,7 @@ def test_get_athlete_power_curves(monkeypatch):
     result = asyncio.run(
         get_athlete_power_curves(
             activity_type="Ride",
-            athlete_id="i1",
+            
         )
     )
     assert "Power Curves (Ride):" in result
@@ -492,7 +492,7 @@ def test_get_athlete_power_curves_custom_durations(monkeypatch):
         get_athlete_power_curves(
             activity_type="Ride",
             durations=[5, 60],
-            athlete_id="i1",
+            
         )
     )
     assert "5s:" in result
@@ -518,7 +518,7 @@ def test_get_athlete_power_curves_without_normalised(monkeypatch):
         get_athlete_power_curves(
             activity_type="Ride",
             include_normalised=False,
-            athlete_id="i1",
+            
         )
     )
     assert "W/kg" not in result
@@ -542,7 +542,7 @@ def test_get_athlete_power_curves_date_validation(monkeypatch):
         get_athlete_power_curves(
             activity_type="Ride",
             start_date="2026-01-01",
-            athlete_id="i1",
+            
         )
     )
     assert "Error" in result
@@ -566,7 +566,7 @@ def test_get_athlete_power_curves_no_curves_selected(monkeypatch):
             activity_type="Ride",
             this_season=False,
             last_season=False,
-            athlete_id="i1",
+            
         )
     )
     assert "Error" in result
@@ -590,7 +590,7 @@ def test_get_custom_items(monkeypatch):
     monkeypatch.setattr(
         "intervals_mcp_server.tools.custom_items.make_intervals_request", fake_request
     )
-    result = asyncio.run(get_custom_items(athlete_id="1"))
+    result = asyncio.run(get_custom_items())
     assert "Custom Items:" in result
     assert "HR Zones" in result
     assert "ZONES" in result
@@ -617,7 +617,7 @@ def test_get_custom_item_by_id(monkeypatch):
     monkeypatch.setattr(
         "intervals_mcp_server.tools.custom_items.make_intervals_request", fake_request
     )
-    result = asyncio.run(get_custom_item_by_id(item_id=1, athlete_id="1"))
+    result = asyncio.run(get_custom_item_by_id(item_id=1))
     assert "Custom Item Details:" in result
     assert "HR Zones" in result
     assert "ZONES" in result
@@ -645,7 +645,7 @@ def test_create_custom_item(monkeypatch):
         "intervals_mcp_server.tools.custom_items.make_intervals_request", fake_request
     )
     result = asyncio.run(
-        create_custom_item(name="New Chart", item_type="FITNESS_CHART", athlete_id="1")
+        create_custom_item(name="New Chart", item_type="FITNESS_CHART")
     )
     assert "Successfully created custom item:" in result
     assert "New Chart" in result
@@ -675,7 +675,7 @@ def test_create_custom_item_with_string_content(monkeypatch):
         create_custom_item(
             name="Activity Field",
             item_type="ACTIVITY_FIELD",
-            athlete_id="1",
+            
             content='{"expression": "icu_training_load"}',  # type: ignore[arg-type]
         )
     )
@@ -705,7 +705,7 @@ def test_update_custom_item(monkeypatch):
         "intervals_mcp_server.tools.custom_items.make_intervals_request", fake_request
     )
     result = asyncio.run(
-        update_custom_item(item_id=1, name="Updated Chart", athlete_id="1")
+        update_custom_item(item_id=1, name="Updated Chart")
     )
     assert "Successfully updated custom item:" in result
     assert "Updated Chart" in result
@@ -724,7 +724,7 @@ def test_delete_custom_item(monkeypatch):
     monkeypatch.setattr(
         "intervals_mcp_server.tools.custom_items.make_intervals_request", fake_request
     )
-    result = asyncio.run(delete_custom_item(item_id=1, athlete_id="1"))
+    result = asyncio.run(delete_custom_item(item_id=1))
     assert "Successfully deleted" in result
 
 
@@ -744,7 +744,7 @@ def test_create_custom_item_with_invalid_json_content(monkeypatch):
         create_custom_item(
             name="Bad Item",
             item_type="FITNESS_CHART",
-            athlete_id="1",
+            
             content="not valid json",  # type: ignore[arg-type]
         )
     )
@@ -790,7 +790,7 @@ def test_get_gear_list(monkeypatch):
         "intervals_mcp_server.tools.gear.make_intervals_request", fake_request
     )
 
-    result = asyncio.run(get_gear_list(athlete_id="i1"))
+    result = asyncio.run(get_gear_list())
 
     assert "Gear catalog for athlete i1:" in result
     assert "Litening Air" in result
@@ -814,7 +814,7 @@ def test_get_gear_list_empty(monkeypatch):
         "intervals_mcp_server.tools.gear.make_intervals_request", fake_request
     )
 
-    result = asyncio.run(get_gear_list(athlete_id="i1"))
+    result = asyncio.run(get_gear_list())
     assert "No gear found" in result
 
 
@@ -845,15 +845,15 @@ def test_get_gear_list_cache_and_refresh(monkeypatch):
     )
 
     # First call: cache cold, one API hit expected.
-    asyncio.run(get_gear_list(athlete_id="i1"))
+    asyncio.run(get_gear_list())
     assert call_count["n"] == 1
 
     # Second call: cache warm, no additional API hit.
-    asyncio.run(get_gear_list(athlete_id="i1"))
+    asyncio.run(get_gear_list())
     assert call_count["n"] == 1
 
     # refresh=True busts the cache and triggers a fresh fetch.
-    asyncio.run(get_gear_list(athlete_id="i1", refresh=True))
+    asyncio.run(get_gear_list(refresh=True))
     assert call_count["n"] == 2
 
 
@@ -944,7 +944,7 @@ def test_get_activities_resolves_gear_name(monkeypatch):
         "intervals_mcp_server.tools.gear.make_intervals_request", fake_request
     )
 
-    result = asyncio.run(get_activities(athlete_id="1", limit=2, include_unnamed=True))
+    result = asyncio.run(get_activities(limit=2, include_unnamed=True))
     assert "Ride 1" in result
     assert "Ride 2" in result
     assert "Name: Litening Air" in result
diff --git a/tests/test_tool_auth.py b/tests/test_tool_auth.py
new file mode 100644
index 0000000..37a8e21
--- /dev/null
+++ b/tests/test_tool_auth.py
@@ -0,0 +1,55 @@
+"""
+Every tool must refuse to act (and surface a helpful message) when the caller
+has no usable credentials — a disabled/unapproved user, or one who hasn't set up
+their Intervals.icu key. This guards the admin-approval gate: there is no tool
+parameter a caller can pass to bypass it.
+"""
+
+import asyncio
+
+import pytest
+
+from intervals_mcp_server import credentials
+from intervals_mcp_server.credentials import CredentialError
+from intervals_mcp_server.tools import activities, custom_items, events, gear, power_curves, wellness
+
+# (tool callable, minimal required positional args)
+TOOL_CALLS = [
+    (activities.get_activities, ()),
+    (activities.get_activity_details, ("1",)),
+    (activities.get_activity_intervals, ("1",)),
+    (activities.get_activity_streams, ("1",)),
+    (activities.get_activity_messages, ("1",)),
+    (activities.add_activity_message, ("1", "hi")),
+    (events.get_events, ()),
+    (events.get_event_by_id, ("e1",)),
+    (events.delete_event, ("e1",)),
+    (events.delete_events_by_date_range, ("2026-07-01", "2026-07-31")),
+    (events.add_or_update_event, ("Ride", "Name")),
+    (events.add_or_update_note, ("Name", "desc")),
+    (wellness.get_wellness_data, ()),
+    (power_curves.get_athlete_power_curves, ()),
+    (gear.get_gear_list, ()),
+    (custom_items.get_custom_items, ()),
+    (custom_items.get_custom_item_by_id, (1,)),
+    (custom_items.create_custom_item, ("N", "TYPE")),
+    (custom_items.update_custom_item, (1,)),
+    (custom_items.delete_custom_item, (1,)),
+]
+
+
+async def _deny():
+    raise CredentialError("ACCOUNT NOT APPROVED")
+
+
+@pytest.mark.parametrize("func,args", TOOL_CALLS, ids=[f.__name__ for f, _ in TOOL_CALLS])
+def test_tool_returns_message_when_unauthorized(monkeypatch, func, args):
+    # override the autouse fixture: the caller has no usable credentials
+    monkeypatch.setattr(credentials, "resolve_caller_credentials", _deny)
+    result = asyncio.run(func(*args))
+    assert result == "ACCOUNT NOT APPROVED"
+
+
+def test_all_20_tools_covered():
+    """Guard: if a tool is added, add it here so its auth gate is tested."""
+    assert len(TOOL_CALLS) == 20