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

Annotations already declare readOnlyHint/destructiveHint=false, so the safety profile is covered; the description goes well beyond that. It discloses the zero-count interpretation caveat, the return shape (breach count plus named sources), and an important failure mode (missing RELAYSHIELD_API_KEY returns setup instructions instead of calling the API).

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?

Three tight sentences: what it does, how to call it, and what comes back. The key caveat (zero ≠ safe) is placed early and every sentence carries distinct 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?

With no output schema, the description compensates by describing the return value (count plus named sources) and the setup-instructions fallback when the API key is absent. For a one-parameter read-only lookup, nothing an agent needs to call 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 email parameter, including case-insensitivity, so the description's 'Provide email' adds nothing over the schema. Baseline 3 is appropriate when the schema fully documents the parameter.

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: checks an email address against known data breaches. The resource is distinct from the sibling tools (check_link, check_wallet), but the description never names those alternatives, so the differentiation is left to inference rather than made explicit.

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?

It supplies a genuinely useful interpretive rule ('a count of zero means no breaches were found in the corpus, not that the address is safe') and the API-key prerequisite, but gives no explicit when-to-use-this-vs-check_email guidance or any exclusion criteria. Usage is implied rather than directed.

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