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

Annotations only say it is a non-read-only, non-destructive, non-idempotent, closed-world write. The description adds substantial context beyond that: the required HMAC secret, the two named failure modes (invalid_request, not_configured), and the 60s freshness window implied by the timestamp parameter.

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?

Front-loads the core action and signing scheme, then tacks on refusal codes and the alternative endpoint. Dense and largely waste-free, though the bracketed tags ('[free, no key] [limited]') are cryptic filler.

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 four-required-parameter mutation with no output schema, it covers auth requirements, failure cases, and the alternate path. It stops short of describing what the minted key response looks like, which is a minor gap given there is no output schema.

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 100%, so each parameter is already documented in the schema. The description restates the signature construction but adds no format or constraint detail the schema lacks, so the baseline 3 is appropriate.

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 and resource ('Mint a free-tier API key without email') and the exact mechanism (HMAC-SHA256 over agent_id + timestamp + nonce). No sibling tool does anything comparable, so the agent can place it immediately.

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 a clear precondition (requires MACHINE_MINT_SECRET) and routes to an explicit alternative when the secret is absent ('No secret: use POST /keys/request'). It does not spell out the broader when-to-use case versus the other key/booking siblings, but the fallback routing is genuinely useful.

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