check_spf

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

Annotations already declare readOnlyHint, idempotentHint, openWorldHint and destructiveHint=false, so the safety profile is covered. The description adds genuine value beyond them by disclosing what the output contains: whitelisted senders, flagged syntax errors, and the exposed trust surface. It stops short of noting rate limits or how stale/cached results are signalled.

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 action and its outputs, with the usage cue and audit context at the end. There is mild redundancy between "Lists all IP addresses and third-party senders authorised to send email" and "Use when you need to know who is permitted to send email", but nothing is wasted at length.

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?

An output schema exists, so return-shape explanation is not required, and annotations carry the safety profile; the description covers scope, outputs and a usage cue. It is only slightly thin on how this tool relates to resolve_spf_chain and scan_domain, which matters given the dense sibling set.

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% and every parameter (domain, format enum, force_refresh) is documented in the schema itself. The description adds no parameter-level meaning, such as what 'full' vs 'compact' actually changes or when to set force_refresh beyond the schema note, so baseline 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+resource ("look up and validate the SPF record for a domain") and enumerates the outputs (IPs, third-party senders, syntax errors, trust surface). It is clearly distinguishable from DMARC/DKIM siblings by resource, though the near-neighbour sibling resolve_spf_chain is never mentioned, so full sibling differentiation is incomplete.

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 an implied trigger condition, and "Part of the scan_domain audit" hints at orchestration context. But there are no exclusions and no routing to alternatives such as resolve_spf_chain (for recursive/flattened lookups) or scan_domain (for a full audit), leaving the agent to infer.

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