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

Annotations already declare readOnlyHint, idempotentHint and destructiveHint=false, but the description adds meaningfully beyond them: the secret is request-body only and never stored, the call is billed after 10 free calls/day via x402 or X-API-Key credits, and this host serves it. That pricing/auth/data-handling disclosure is real value not present in the structured fields. It stops short of describing mismatch behavior or output shape in depth, keeping it at 4 rather than 5.

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?

The purpose, return value and data-handling caveat are front-loaded, and the commercial/payment details are compactly appended. It is dense across four separate concerns (behavior, use case, billing, hosting) but no sentence is clearly redundant for an agent deciding whether and how to call it.

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 five fully documented parameters, an output schema, and rich annotations, the remaining burden is mostly behavioral, and the description covers return type, secret handling, auth and quota. The only notable omission is what happens on a non-matching signature (false vs error) and whether comparison is timing-safe.

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 every parameter already has a description with examples, so the schema does the heavy lifting. The description reinforces the algorithm set and secret handling but adds nothing about signatureEncoding or the auto-detection of hex vs base64, which is the one parameter where extra meaning would have helped.

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 — verify an HMAC over a message with a caller-supplied secret — and names the supported hash families (SHA-256/1/384/512) plus the return value (valid bool). It does not explicitly distinguish itself from the close sibling signature_verify, so differentiation is left implicit.

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 one concrete use case ("for webhook authenticity checks"), which anchors when to reach for it. There is no guidance on when not to use it and no named alternative such as signature_verify or approval_verify, so an agent must infer the choice from sibling names alone.

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