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

Annotations already cover readOnly, idempotent, openWorld and non-destructive, so the safety profile is handled. The description adds value by disclosing the breadth of external lookups (blocklists, MTA-STS, BIMI, DKIM on common selectors), implying multiple network calls, though it omits latency, rate limits or result format.

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?

Two sentences, zero waste. The scope of checks is front-loaded and the usage cue follows immediately, making it easy to scan.

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 enumerating what is inspected, which is enough for an agent to know the result is a multi-check health report. Minor gaps (return shape, per-check failure semantics) remain but are not blocking.

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?

Only one parameter ('domain'), and schema coverage is 100% with a clear example in the schema itself. The description adds no format or constraint detail beyond the schema, so the baseline 3 is appropriate.

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?

Names a specific verb+resource ('check everything about a domain's email setup') and enumerates the exact checks performed (SPF, DMARC, MX, DKIM, blocklists, MTA-STS, TLS-RPT, BIMI). This clearly distinguishes it from the granular siblings like check_spf, check_dkim and check_dmarc.

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?

Explicitly routes the agent with 'Use it for a general question such as "is email set up correctly for example.com"', which signals aggregate use versus the single-check siblings. It stops short of naming those siblings or stating when NOT to use it (e.g., for a targeted DKIM-only check).

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