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

Annotations already establish readOnlyHint=true and openWorldHint=true, so the agent knows this is a safe network-touching read. The description usefully discloses that the check spans two channels (DNS TXT plus an HTTPS-fetched policy file), which is real added context, but it says nothing about caching, timeouts, or what a missing policy yields.

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 front-loaded sentence with a compact parenthetical enumerating the checked artifacts; no filler sentences. Slightly clause-dense, but every clause carries 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 an output schema present, return-value documentation is not required, and the description covers the full scope of the check (policy records, policy file, mode, MX coverage, TLS-RPT). Only the absence of failure/negative-result behavior keeps it from a 5.

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, and the schema already documents it fully (100% coverage) including the 'no scheme or path' constraint. Baseline 3 applies since the description adds no format or edge-case meaning beyond the 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) and a specific resource (the domain's MTA-STS policy) and enumerates the exact artifacts inspected: the _mta-sts TXT record, the HTTPS policy file, its mode, MX coverage, and the TLS-RPT record. This is far more informative than a generic 'check' tool, though it never explicitly contrasts itself with sibling checks like check_dmarc or check_spf.

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?

The description says what is checked but never when to reach for this tool versus alternatives, nor any prerequisites (e.g. that MTA-STS/TLS-RPT are meaningful only alongside DMARC/DKIM context). Usage is only inferable from the protocol name, which is minimal guidance.

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