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

Goes beyond the annotations by disclosing the trust model: the verification key is fetched from the receipt's own `iss` claim, with a rationale for why. This explains the network behavior behind openWorldHint. It does not say what happens when the issuer is unreachable or the signature fails, though an output schema exists.

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?

Front-loaded with the core action, followed by a short security caveat and a usage note. The all-caps, emoji-prefixed warning is slightly heavy formatting for the amount of information conveyed, but every sentence carries real content.

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 read-only tool with an output schema, the description covers what an agent needs: input format via the schema, the trust/network behavior, and the intended scope of receipts. Failure semantics are left to the output schema.

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 parameter is fully described as a compact JWS string with examples. The description adds only indirect meaning (the issuer is read from the token itself, so no key parameter is needed). Baseline 3 applies.

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 ('Check a receipt's signature against the key its issuer publishes'), which is unambiguous and clearly distinct from the escrow payment siblings that create or settle receipts.

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?

'Use this on receipts from anywhere, including ones this server did not produce' gives a clear inclusion criterion and implicitly contrasts with receipts this server generated. It stops short of naming a sibling or stating when-not-to-use (e.g. versus check_escrow_payment).

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