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

With no annotations, the description carries the full burden and does well: it discloses what is inspected, the returned fields (risk_score and accept/reject), and a concrete quota ('20 checks per day'). It omits auth requirements and latency, and doesn't explicitly state it performs no mutation, but the depth of disclosed behavior is well above baseline.

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?

A single dense sentence with the risk domain and checks front-loaded, followed by return values and the quota. Every clause earns its place with no 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?

There is no output schema, but the description names the two return values and enumerates the checks performed, so an agent understands both inputs and outputs. Minor gaps: no note on error behavior for malformed input or what risk_score's scale means.

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 0%, so the description must compensate. It clarifies that exactly one address is accepted and, via the 'gmial.com -> gmail.com' example, gives a concrete sense of the input format. With only a single required string parameter this is close to sufficient, though it never states expected normalization or validation of the input.

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 (verify/check) and resource (one email address) and immediately narrows the purpose to 'signup-abuse risk', enumerating the exact checks (disposable domain, MX, role mailbox, free provider, typo suggestion). An agent knows precisely what this does and it is unmistakable given the unrelated siblings.

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 'signup-abuse risk' framing implies the use case (validating emails at signup), but there is no explicit when-to-use/when-not guidance or named alternative. With unrelated siblings this is unlikely to cause misrouting, so implied usage is adequate but not strong.

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