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

With no annotations, the description carries the whole burden and does well: it discloses that the tool returns a URL rather than a file, that the actual download happens off-platform on cityheart.run, that it costs €9.90 via Stripe, and that the chat never charges. It omits failure behavior (e.g. route not public, already purchased) and what exactly the URL object contains.

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, front-loaded with the return value, then the payment context that prevents an agent from claiming it charged the user, then the sequencing rule. Nothing is redundant.

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 one-parameter tool with no annotations or output schema, the description covers purpose, the off-platform payment model, and the confirmation gate, which is the risky part of this call. Only the response shape and error conditions remain unstated, and those are modest gaps.

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% and the single slug parameter is documented with an example, so the baseline is 3. The description adds only one nuance beyond the schema — that the slug must identify a *public* route — which is useful but minor.

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: 'Return the GPX download / checkout URL for a specific public route.' It also implicitly separates itself from generate_heart_route and get_route_details by positioning itself as the post-selection export step, so an agent can place it without opening any 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 ordering rule — use after the user has picked a final route (find / get_details) and confirms they want it — which is exactly the condition an agent needs. It does not state when not to call it (e.g. unpriced or unpublished routes), so it stops short of full when/when-not guidance.

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