HMAC Verify

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

The description adds the valuable constant-time comparison detail, which is not in annotations. However, it does not disclose the return value or behavior on mismatch (e.g., boolean vs error), which is a gap given no output schema. Since annotations already cover readOnly, idempotent, and non-destructive, the added timing-safety context earns a 4.

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 description is two sentences, front-loaded with the core purpose and immediately followed by a usage directive. No fluff or redundancy—every word adds value.

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?

The description gives purpose and usage but omits the return type or error handling, which is critical for an agent to know how to process the result without an output schema. It also does not mention the algorithm default or encoding specifics, though those are in the schema. Overall adequate but not fully complete for a verification 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 description coverage is only 25% (only the signature parameter is described). The tool description does not explain the 'secret' (shared key) or 'algorithm' parameters at all, and only vaguely references 'message' and 'expected HMAC'. It fails to compensate for the sparse schema, leaving the agent to infer parameter semantics from the tool name.

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 action ('Check a message against an expected HMAC') with a clear resource (message vs HMAC) and adds a concrete use case (validate inbound webhook). It implicitly distinguishes from the sibling hmac_sign by focusing on verification, and explicitly contrasts with manual string comparison.

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 provides a direct directive: 'Use this to validate an inbound webhook signature rather than comparing strings yourself.' This tells the agent exactly when to use the tool and what to avoid (manual comparison), making the selection decision unambiguous.

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