Expire unpaid session (cancel payment link)

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

With no annotations provided, the description carries the full burden of behavioral disclosure. It reveals that the tool only works on UNPAID sessions, invalidates the payment URL, returns no body, and suggests using 'get_session_status' for verification. While it doesn't cover error cases or authorization requirements, it provides solid insight into the tool's runtime behavior.

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, each with a distinct purpose: the action, the use case, and the response behavior plus follow-up. It is front-loaded with the core function and contains no redundant or extraneous 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 tool with a single parameter and no output schema, the description adequately covers the purpose, the precondition (UNPAID), the effect (payment URL becomes unpayable), and the verification step (use get_session_status). Minor gaps remain around error handling for invalid or paid session IDs, but the description is sufficient for correct selection and invocation.

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?

The input schema already fully describes the only parameter 'session_id' as 'Session id (acquiring or checkout)'. The description adds context about the session being 'UNPAID' but does not provide additional parameter-specific syntax or formatting details. Since schema coverage is 100%, the baseline score of 3 is appropriate.

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 specifies the verb 'Invalidate' and the resource 'UNPAID session', with a concrete outcome: the payment URL can no longer be paid. It differentiates from siblings like 'void_session' by emphasizing the 'UNPAID' constraint, making the tool's purpose distinct.

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 explicitly states when to use the tool: 'Use this to cancel a payment link that was created by mistake or is no longer needed.' It also provides a follow-up instruction to 'check the result with get_session_status,' which guides the agent on next steps and differentiates from alternative session-management tools.

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