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

Annotations already declare readOnlyHint=true and openWorldHint=true, so the safety profile is covered and no contradiction exists. The description adds the default format value, but says nothing about the returned payload (binary stream, URL, or base64), file-size/rate-limit considerations, or whether ORIGINAL returns the raw uploaded file.

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?

The format list is stated twice — once as prose and again as a verbatim enum transcription with the type name `ActivityDownloadFormat` — which is pure repetition. The key fact (default) is present but buried in the duplicate.

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?

With no output schema, the description carries the burden of explaining the return value, yet it never says whether the response is a file stream, a URL, or encoded content. Format options and the default are covered, so it is minimally viable for a 2-parameter download tool but not complete.

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 description coverage is 50% (activityId documented as 'Numeric id'; format has an enum but no default). The description compensates by supplying the missing default ('"ORIGINAL" (the default)') and naming what the format controls, which is genuine value beyond the schema — though it never explains what 'ORIGINAL' actually yields.

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 ('Downloads an activity file') and enumerates the exact output formats, so the agent knows precisely what the tool produces. It does not, however, differentiate itself from the similar-sounding siblings download_workout, download_course_gpx, and download_health_snapshot.

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?

There is no when-to-use guidance: nothing says to prefer this over download_workout or download_course_gpx, nor whether this streams a file versus returning metadata (get_activity). Usage is only inferable from the verb 'downloads'.

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