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

With no annotations provided, the description carries the full burden. It discloses a non-obvious behavior: the tool returns existing matches as well as a deep-link to the builder, rather than immediately creating a route. It also states that optional parameters pre-fill the builder, making the effect transparent. However, it does not clarify whether this is a read-only operation or what happens if no existing matches are found, leaving minor gaps.

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 three sentences, front-loaded with the core action. Every sentence adds distinct value: purpose/behavior, usage guidance, and param pre-fill note. No filler or redundant phrasing.

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 tool with 5 parameters, no annotations, and no output schema, the description covers the main purpose, hybrid return behavior, usage trigger, and one param nuance. It does not detail the exact response structure (e.g., shape of the deep-link) or edge cases like missing inventory matches, but overall it provides enough context for an agent to invoke correctly.

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%, giving baseline 3. The description adds value by explaining that 'dedication / cause_url pre-fill the builder fields', connecting these parameters to their effect on the deep-link URL. This goes beyond the schema's descriptions (which focus on GPX/Strava metadata) and clarifies the configuration role of these params.

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 uses a specific verb+resource: 'Start a new heart-shaped route for a given city.' It clearly distinguishes from siblings by stating it returns both existing AI-validated matches and a deep-link to the live builder, differentiating it from find_heart_route_in_city. The phrase 'for a given city' ties directly to the required city parameter.

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?

Explicit guidance is provided: 'Use when the user explicitly wants a NEW heart, or when an existing match is "close enough but not personal yet".' This gives clear when-to-use and implies when not to use (when an existing personalized match is already acceptable). It also explains the pre-fill behavior, adding context for optional parameters.

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