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

Annotations already cover the safety profile (readOnly, idempotent, non-destructive), and the description usefully adds the output semantics: which registered company declares the key directory, the declared agent, its mandate, and current validity. With no output schema present, this return-value disclosure is genuinely load-bearing, though it says nothing about lookup failure modes or stale entries.

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?

Three sentences, front-loaded with the real-world trigger and followed by the call instruction and the return contents. Every sentence carries information, though the closing contrast sentence is slightly longer than needed to make the point.

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 one fully documented parameter, no output schema, and annotations covering safety, the description supplies exactly what is missing: where the input comes from and what the response tells the caller. An agent has everything needed to invoke it 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% and the single parameter's description already explains both accepted forms (bare https address or full header value). The description repeats that flexibility ('pass the https address ... or the whole header value') but adds no parsing rules, normalization behavior, or error handling beyond 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 and resource (verifying the entity behind a Signature-Agent header) and explains the semantic result: company, agent, mandate and validity. It conceptually separates itself from raw signature validation ('a valid signature only shows which key signed'), but never names its siblings verify_agent or search_registry, so an agent cannot tell from text alone how it differs from those tools.

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?

It gives a clear trigger condition: use when a request was signed with HTTP Message Signatures (Web Bot Auth) and carries a Signature-Agent header. However, it offers no exclusions or routing rules versus verify_agent or search_registry, so the agent must infer which of the three to call.

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