check_mta_sts

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

Annotations already declare read-only, idempotent, non-destructive, open-world behavior, so the bar is lower. The description still adds real substance: it discloses the two network operations performed (DNS TXT lookup and policy file fetch) and what is reported (mode enforce/testing/none plus MX coverage). It does not mention caching behavior, though the schema's force_refresh parameter covers that.

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 sentences, each carrying distinct information: what is checked, how it is checked and reported, and when to use it versus the sibling. The core purpose is front-loaded with no filler.

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?

Input schema is fully documented, an output schema exists so return values need no explanation, and annotations cover the safety profile. The description fills the remaining gap by explaining the mechanism and the sibling relationship — nothing an agent needs in order to call this 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% with all three parameters documented, including the enum for format and the cache-bypass semantics of force_refresh. The description adds no parameter-level detail beyond what the schema provides, so the baseline of 3 applies.

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 whether a domain enforces SMTP TLS via MTA-STS against downgrade attacks. It also names the exact mechanisms queried (_mta-sts.<domain> record plus policy file) and contrasts itself with check_dane, so the agent can distinguish it from dozens of sibling check_* tools without opening a schema.

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?

Gives an explicit use case ('verify whether inbound SMTP is protected against TLS downgrade or MITM'), names the alternative that covers a different mechanism ('distinct from check_dane which uses TLSA pinning'), and situates it in the larger workflow ('Part of the scan_domain audit').

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