check_spf

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

The annotations already declare readOnlyHint, idempotentHint, openWorldHint and destructiveHint=false, so the safety profile is fully covered. The description restates what the tool returns (IP list, third-party senders, syntax errors, whitelisted mail servers), which largely duplicates the output schema rather than adding non-obvious behavior such as cache semantics or fallback handling.

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, front-loaded with the core action, with no filler. The parenthetical '(which mail servers are whitelisted)' is mildly redundant with the preceding 'trust surface' phrasing but still clarifies terminology.

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 annotations covering safety, a 100%-covered schema, an output schema handling return values, and only one required parameter, the description is nearly complete. The one omission is sibling disambiguation against resolve_spf_chain, which matters in a tool set this dense.

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 baseline is 3. The description says nothing about the optional 'format' or 'force_refresh' parameters, so it adds no meaning beyond the schema, which already documents all three.

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?

The description opens with a specific verb+resource ('Look up and validate the SPF record for a domain') and enumerates what the result contains. It is clearly distinct from the many unrelated check_* siblings, but it does not distinguish itself from resolve_spf_chain, the closest SPF-related sibling.

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?

'Use when you need to know who is permitted to send email as a domain' gives a genuine usage trigger, and 'Part of the scan_domain audit' situates it in a workflow. However, there are no when-not conditions and no routing to the obvious alternative resolve_spf_chain, so the guidance is implied rather than explicit.

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