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

Annotations already declare readOnly, idempotent, non-destructive, and closed-world, so safety is covered. The description adds real context beyond that: it is free, requires no profile/auth, returns a boolean 'valid' plus a kind and contents, and returns a reason on failure ('why says what to check'). It stops short of describing failure modes like malformed base64 or oversized payloads.

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?

Purpose is front-loaded and the text stays within a few sentences. The long parenthetical enumeration of receipt types is somewhat list-heavy, but each item disambiguates a real accepted input class, and the closing public-key URL is a useful escape hatch rather than 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?

With no output schema, the description carries the return-value burden and does so — 'valid (true or false)', the kind if valid, what it says, and a diagnostic reason otherwise. Auth (none needed), cost (free), and an alternate verification route are all present, so an agent has everything required to call and interpret this tool.

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%, which alone would justify a 3. The description goes further by stressing that both payload and signature must be passed 'exactly as you got them' — meaning no re-serialization or re-encoding — which is essential when a signature is being validated against raw bytes and is not stated in the schema.

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 states a specific verb+resource ('Check that a receipt or record really was signed by Agent Anthill and hasn't been changed') and enumerates the exact artifact types it applies to (item receipts, Arena/Off the Record records, Forget-Me-Not seals, Pass the Leaf line records). This cleanly separates it from the read/write/info siblings in the same namespace.

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?

Clear context is given — hand over a payload and signature you already possess — plus an explicit constraint ('exactly as you got them'), a cost/auth note ('Free, no profile needed'), and a named alternative path (verify yourself with the public key). It lacks an explicit when-not clause, but no plausible competing tool exists for the same job.

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