Download original activity file (FIT)

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

Annotations already declare readOnly/idempotent/non-destructive/openWorld, but the description adds substantial context beyond them: behavior differs when GARMIN_DOWNLOAD_DIR is set (file saved, path returned) versus inline base64 embedded resource, with a 3 MB size cap. That size limit and environment-dependent return mode are exactly the kind of operational detail an agent needs to plan around.

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?

Three sentences ordered by importance: what you get, how it is delivered, and when to use a smaller alternative. No redundancy with the title or annotations.

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 single-parameter read tool with no output schema, the description covers the return modality, environment-dependent save path, size ceiling, and the cheaper sibling alternative. Nothing an agent needs to invoke or interpret it is 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?

Only one parameter and schema coverage is 100%, with the schema itself explaining that activityId is the numeric ID returned by garmin_search_activities. The description adds no further parameter-level meaning, so the baseline 3 applies — the schema, not the description, carries the semantics.

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 the original device-recorded file for an activity — and clarifies the typical payload (ZIP containing .FIT with GPS, HR, power, cadence samples). It explicitly distinguishes itself from garmin_get_activity, so an agent can route without opening either schema.

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 an explicit alternative with the condition that selects it: 'For summaries, splits or metrics, prefer garmin_get_activity: it is much smaller.' It also distinguishes the local-save vs inline-return cases, leaving no routing ambiguity.

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