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

Annotations already indicate a non-read-only, non-destructive operation, but the description adds meaningful behavior beyond that: the rate limit of once per hour and the conditional email substitution when a match is waiting. There is no contradiction with the annotations, and these extra details materially affect agent decisions.

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 three sentences with no filler. It front-loads the use case, then the action, then exclusions/rate-limit/conditional behavior. Every sentence carries decision-relevant information.

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 tool with one optional parameter, no output schema, and clear annotations, the description covers all necessary context: when to use, what it does, what it does not do, rate limiting, and a state-dependent behavior. Nothing an agent needs to invoke it correctly is missing.

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% for the single api_key parameter, which already explains when to pass it vs. omit it. The tool description does not add additional parameter-level meaning beyond what the schema provides, so the baseline of 3 applies.

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 the exact trigger condition ('Use when your human says they did not receive the email confirming you registered them, or cannot find it') and states a specific verb + resource ('Re-sends that email to the address on file, with the confirm link'). It also explicitly contrasts itself with recover_key, so an agent can immediately distinguish it from that sibling.

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?

The description provides explicit when-to-use guidance (user reports missing confirmation email) and an explicit exclusion ('This is NOT recover_key: this does not touch your API key'). It also notes the rate limit ('Works at most once an hour') and the conditional behavior for a waiting match, which are essential for correct invocation timing.

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