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

With no annotations provided, the description carries the full burden and does disclose non-obvious behaviors: retries require the same idempotency_key, and the tool never auto-routes or falls back to a prior winner. It also explains auth requirements for each payment path. It stops short of describing side effects, return format, or failure behavior, but the disclosed traits are meaningful.

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 two sentences, front-loaded with the core action, and every clause earns its place. There is no fluff or repetition of schema fields, making it highly efficient for an agent to parse.

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?

The description covers key operational aspects (payment auth, idempotency, no-fallback), which is good for a tool with no annotations and no output schema. However, it omits the essential semantics of the 'input' parameter and any description of the response or errors, leaving the tool incompletely specified for an agent to use confidently without external knowledge.

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 description adds value by clarifying the relationship between payment_path, api_key, and agent_key, and by emphasizing that capability_id must be explicit and idempotency_key must be reused for retries. However, the 'input' parameter—which is required and has no schema description—is entirely unaddressed, leaving a significant gap despite the 50% schema coverage.

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 'Call one explicit capability id', which is a specific verb+resource statement that clearly distinguishes this tool from siblings like capability_get (inspect) or capabilities_list (list). The emphasis on 'explicit' and 'never auto-route or fall back to a prior winner' further differentiates it from any potential routing-based alternatives.

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 contextual guidance on payment paths ('Use x402 with an agent_key outside bounties, or balance with an api_key for a Stripe-topped-up wallet') and idempotency for retries. However, it does not explicitly name alternatives or state when NOT to use this tool versus siblings, so the guidance is implied rather than explicit.

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