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 key behaviors: idempotency requirements ('same idempotency_key'), no auto-routing or fallback to prior winners, and the conditional auth/payment requirements. It does not mention return format or error behavior, but the disclosed traits are meaningful and go beyond the schema.

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 short, purposeful sentences. It front-loads the core purpose, then adds conditional usage details and retry behavior. Every sentence earns its place with no redundant or vague filler.

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 6-parameter tool with no output schema, the description should ideally cover input semantics, return value, and side effects. It covers payment, idempotency, and no-fallback behavior, but leaves 'input' undefined and does not describe what happens on success or failure. Given the complexity of executing a capability, this is a notable gap, so completeness is only adequate.

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 50%, so the description must compensate. It adds context for payment_path and the conditional api_key/agent_key fields, and explains idempotency_key usage for retries. However, it does not explain the 'input' parameter, which is completely unspecified in both schema and description, leaving a significant gap. It adds value for some params but not all.

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 starts with 'Call one explicit capability id', clearly stating the action and resource. This distinguishes it from sibling tools like capability_get (retrieval) and capability_register (registration). The explicit mention of 'explicitly selected capability' reinforces its specific purpose.

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 clear context on choosing payment paths: 'Use x402 with an agent_key outside bounties, or balance with an api_key for a Stripe-topped-up wallet.' It also gives retry guidance: 'Retries require the same idempotency_key and never auto-route or fall back to a prior winner.' However, it does not explicitly state when to use this tool instead of alternatives like capability_get or capabilities_list, though the purpose is fairly obvious.

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