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

Annotations already cover safety (readOnly, idempotent, non-destructive, closed-world); the description adds value with rate limiting ('limited per address'), the no-credential posture, and a genuine security warning that the secret travels in the request. This is meaningful context beyond the structured hints, though it doesn't discuss latency or error behavior.

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?

A single dense paragraph, front-loaded with the action and followed by the caveats that matter. It carries a lot of useful content without wasted words, though the flow is slightly run-on.

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 does state the return nature ('Answers whether it is valid'), and it covers the security and rate-limit context an agent needs. Complete enough to invoke correctly; only error/response-shape detail is absent.

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 each parameter is documented in the schema, so the baseline is 3. The description re-mentions payload size (8 KB), encoding (hex/base64), and prefix, but adds no syntax or format detail beyond what the schema already states.

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+resource ('Check a webhook signature') and grounds it in the product's own signing scheme ('the way Last Price signs them'). It's clearly separable from siblings like ping_webhook, create_webhook, or verify_signed_quote, though it never explicitly names those 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?

Gives real operational context: public endpoint, rate-limited per address, no credential required, and the advice to prefer a test secret. It stops short of explicit when-not-to-use or sibling routing, but there is no obvious competing tool for this exact job.

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