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

Adds real traits beyond the annotations: 'No logging of addresses' (privacy), SMTP probe is 'Slower (1–8 s); some servers block it', and catch-all detection affects result meaning. Slight tension with openWorldHint=false, since DNS/MX lookups and SMTP RCPT probes reach external servers, though this is a labeling nuance rather than a direct contradiction.

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?

Front-loaded with the one-line purpose, then checks, then an example, then the response shape — a sensible scanning order. It is dense but every clause names a distinct capability an agent would otherwise have to discover by trial.

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?

Given three simple params, a full schema and an output schema, the definition covers inputs, cost implications and return semantics well. The only real hole is routing guidance versus the four sibling tools, which the description never addresses.

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%, so the baseline is 3; the schema already explains smtp_check's handshake, latency and blocking. The description only echoes these as 'optional SMTP RCPT probe with catch-all detection and optional SPF/DMARC' and adds no format, cost or edge-case detail the schema lacks.

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?

Opens with a specific verb+resource+scope: 'Full check of one address', where 'one' implicitly separates it from the batch sibling verify_emails. The enumerated check list (syntax, MX, disposable, role, typo, SMTP, SPF/DMARC) makes the tool's remit unmistakable against domain_check, extract_emails and suggest_fix.

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 implied rather than stated: the worked example ('john.doe@gmail.com', smtp_check false) shows a typical default call, and 'optional' flags hint at the cheap-vs-deep tradeoff. However, it never says when to pick verify_email over verify_emails, domain_check or suggest_fix, nor when a caller should skip the tool.

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