Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?

Goes well beyond the annotations: it discloses that Garmin recomputes averageSpeed/averageMovingSpeed, that duration/calories/laps stay unchanged (so laps no longer sum to total), that getActivities lags while getActivity is immediate, and that GarminError is thrown before any request for non-positive/non-finite input. This is exactly the mutation-side-effect reporting an agent needs.

Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.

Is the description appropriately sized, front-loaded, and free of redundancy?

Dense but front-loaded — the core action and unit are in the first clause, with side effects and error behavior following. A few clauses are packed tightly, but nearly every sentence carries distinct information.

Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.

Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?

For a two-parameter mutation with no output schema, the description covers the write semantics, recomputation side effects, read-after-write staleness, and input validation. Nothing an agent needs to call it safely appears to be missing.

Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.

Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?

Schema coverage is only 50% (only activityId is described), but the description compensates by specifying meters is in METERS with no conversion and by flagging the invalid-value rule. It does not restate the activityId type, but the schema already covers that.

Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.

Does the description clearly state what the tool does and how it differs from similar tools?

States a specific verb and resource ('Sets an activity's total distance in meters') and immediately distinguishes itself from the closest sibling by noting `createManualActivity` is the one that takes km. An agent can separate this from the create/import tool family without reading schemas.

Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.

Does the description explain when to use this tool, when not to, or what alternatives exist?

Gives clear usage context ('the edit Garmin Connect offers for treadmill runs') and names the alternative for the km-based path. It stops short of explicit when-not-to-use conditions (e.g. non-treadmill activities), so it is strong but not fully exhaustive.

Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.