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

Annotations already declare readOnlyHint, idempotentHint, openWorldHint, and destructiveHint=false, so the safety profile is covered elsewhere. The description's added value is naming the external third-party dependency (HIBP), which signals network/auth/rate-limit exposure. It does not say what is returned (breach names, counts, dates) or that unlisted addresses simply return no results, so behavioral depth is only moderate.

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 tightly written sentence with the purpose and mechanism front-loaded and no filler. It is efficient, though quite terse for a tool whose output shape is undocumented.

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 one-parameter, read-only lookup with no output schema, the description supplies the essential facts: what is checked and against which corpus. The main residual gap is the absence of any hint about the response (e.g. list of breaches vs. boolean), but the tool's simplicity keeps this from being a serious deficiency.

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?

Single parameter with 100% schema description coverage, so the schema already establishes that 'email' is the address to check. The description adds no format constraints, validation rules, or normalization behavior beyond what the schema states, so it lands at the baseline for a fully documented schema.

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 (check), a specific resource (email address), the outcome tested for (exposure in known data breaches), and the data source (HIBP). Because the resource type is named explicitly, an agent can immediately separate this from siblings like check_domain, check_ip, and check_password.

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?

Usage is only implied by the parameter domain — an agent must infer that it should call this when it has an email rather than a domain, IP, or password. No exclusions or routing guidance are given, e.g. whether to prefer full_scan for a broad sweep or how this relates to check_password.

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