HMAC Sign

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

Annotations already declare the operation readOnly, idempotent, and non-destructive, so the safety profile is covered. The description adds no significant behavioral detail beyond the computation itself and does not discuss return format or failure behavior; this is adequate for a pure function but not especially informative.

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 main sentence is concise and front-loaded with the verb and object. The trailing 'Web version' URL is irrelevant to an agent selecting or invoking the tool and counts as mild noise.

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?

For a simple stateless function, the description plus schema and annotations cover required inputs, supported algorithms, encoding options, and safety. There is no output schema and the description does not explicitly state the return value, but 'Compute an HMAC' makes the output type clear enough for this 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 0%, and the description only repeats 'message' and 'secret key,' adding little beyond the parameter names. It does not explain the encoding output format or the algorithm choice, so the optional parameters rely entirely on self-explanatory enum values and defaults.

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 opens with a specific verb and object—'Compute an HMAC of a message with a secret key'—and reinforces the signing use cases. This contrasts with the sibling hmac_verify tool, so an agent can distinguish the signing operation 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?

Concrete scenarios ('webhook signatures, API request signing') give the agent clear context for when this tool applies. It does not explicitly name alternatives or state when not to use it, so exclusions are missing but the intended use is unmistakable.

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