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

readOnlyHint=true already tells the agent this is a safe read. The description adds genuine behavioral context beyond the annotation: the result only exists after the user has sent mail to the disposable address, which implies a pending/empty state an agent must account for. It does not describe propagation delay or error behavior, so not a 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?

One sentence, front-loaded with the action and result shape, with the precondition attached at the end. No filler and nothing redundant.

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 single-parameter read tool with no output schema, the description names what comes back (score and breakdown) and the prerequisite for the call. It stops short of describing the breakdown structure or a not-ready response, which is the only remaining gap.

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 the sole parameter id is already documented as 'the test id returned by create_mailtest'. The description only reinforces that provenance, adding no new format or usage detail, so the baseline 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?

States a specific verb (fetch) and resource (score and breakdown of a mail test) and ties it to the producing sibling create_mailtest, so an agent can distinguish it from check_blacklist, check_spoofability, and the other diagnostic siblings without opening a 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?

Gives a clear timing precondition: only call once the user has sent their email to the disposable address. It does not name an alternative tool or state what to do if the test is not yet complete, so it stops short of full when/when-not guidance.

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