get_purchase

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

Annotations already mark the call read-only, idempotent, and non-destructive. The description adds valuable behavioral context beyond that: the endpoint has no broader search capability, returned data concerns a real person's transaction and should be reported minimally, and a separate API key is required.

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 front-loaded with the core action and then gives practical guidance. It is somewhat verbose, repeating the no-listing/no-search point in several forms, but nearly every sentence contributes useful behavioral or credential information.

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 annotations and an output schema already present, the description covers everything needed to call it correctly: id sourcing, absence of alternatives, privacy expectations, and authentication. No critical operational detail 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?

With 0% schema coverage, the description carries the parameter documentation burden. It explains where a valid id can come from and what to do when no id is available, which adds real meaning beyond the bare 'id' string in the schema. It stops short of specifying any id format or example, a minor gap.

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 opens with a specific verb and resource: 'Fetch one purchase by id.' It further distinguishes itself from siblings by explicitly stating there is no listing or search endpoint for purchases, so an agent cannot confuse it with any other tool.

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?

It gives explicit provenance for the id (webhook payload, order reference, external record), states that the tool cannot help without an id, and instructs the agent to say so rather than implying a search. It also clarifies the required v1 credential, which affects when the tool is usable.

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