download_fit_file

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

With no annotations, the description carries the full burden. It discloses key behavioral traits: it converts and downloads, and the Returns section explains the conditional behavior—if no output_path is given, it returns a JSON string with base64 content. This is valuable beyond what annotations would provide, though it does not mention mutability or permissions (likely irrelevant for a download).

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 description is well-structured with a concise overview, Args section, and Returns section. Every sentence adds value: format compatibility, parameter explanations, and return behavior. No fluff or redundancy.

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?

The description covers purpose, parameters, and return format, which is sufficient for a 2-param tool. However, it does not address the sibling download_activity_file, leaving potential ambiguity about which download tool to choose. Minor gap given the tool's otherwise clear scope.

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 100% with clear descriptions for both parameters, providing a baseline of 3. The description adds meaning by explaining the effect of omitting output_path (returns base64 content) and provides an example path, enriching the optional parameter semantics beyond the schema's 'optional' note.

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?

The description clearly states 'Download activity as a FIT file' and elaborates that it converts activity to FIT format, which is compatible with Garmin. This specific verb+resource+format clearly distinguishes it from the sibling download_gpx_file and generic download_activity_file.

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?

The description provides context for when to use the tool by mentioning compatibility with Garmin and most training platforms, implying use when FIT format is needed. However, it does not explicitly exclude alternatives like download_gpx_file or download_activity_file, so it lacks explicit when-not-to-use guidance.

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