Validate an email address

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

Annotations only supply readOnlyHint and openWorldHint, so the description carries the rest and does so well: it documents rate-limit behavior (100 requests per 300s), the ratelimit_remain/ratelimit_seconds fields, and specific error codes (401 missing address, 118 rate limited, 119 invalid/depleted API key, implying an API key is required). That is meaningful operational context beyond the structured fields.

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 core purpose is front-loaded in one sentence, but the bulk of the body is an enumerated list of result fields, which duplicates the existing output schema and does not earn its place in a tool description. Structure is readable but somewhat bloated with redundant return-value documentation.

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 two-parameter read-only validation tool, the description covers error semantics, rate limiting, and the meaning of the category enum, which is enough for correct invocation. The return-value section is redundant given the output schema, but nothing essential 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% (email and timeout both documented in the schema), so the baseline is 3. The description adds nothing about the timeout parameter or accepted email formats, but it does explain what the operation does with the address, so it is not below baseline.

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 concrete verb+resource: 'Validate an email address and return info about it.' The resource (email) is distinct from the sibling tools validate_address and validate_phone, so an agent can route correctly even though siblings are never named explicitly.

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?

There is no statement about when to use this tool versus validate_address or validate_phone, and no prerequisites or exclusions are given. Usage is only inferable from the name and first sentence, which is the minimum implied context rather than real guidance.

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