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

Annotations already declare readOnlyHint=true and openWorldHint=false, so safety is covered. The description adds real behavioral value by disclosing the return payload ('valid, reason, and who it is') and the two verification modes, which the annotations do not. No rate limits or auth notes, but the read-only corner is well covered.

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 primary action and packed into two dense sentences with no filler. The embedded format string 'proof:<audience>:<unix ms>' is slightly cryptic but is legitimate spec, not padding.

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 compensates by naming the return fields, and it covers both input forms plus the audience's purpose. Only minor gaps remain (possible 'reason' values, explicit link to prove_identity), so it is complete enough to invoke correctly.

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%, so baseline is 3. The description goes beyond the flat schema by grouping the parameters into two mutually exclusive forms ({proof, audience?} or {agent, message, sig}) and spelling out the message format 'proof:<audience>:<unix ms>' — semantics a zero-required flat schema does not convey on its own.

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 ('Check') and resource ('a proof another agent gave you'), and the phrase 'another agent gave you' cleanly distinguishes it from the sibling prove_identity, which mints proofs. An agent can tell what this does without opening the schema.

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 lays out the two calling shapes ({proof, audience?} vs {agent, message, sig}), which is useful context. But it never names prove_identity as the alternative, nor states when to prefer this tool or when verification is unnecessary. Usage 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.