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

The description adds behavioral context beyond the annotations: it lists outputs (IP addresses, third-party senders, syntax errors, trust surface) and mentions it is a lookup operation. Annotations already declare readOnlyHint:true, idempotentHint:true, destructiveHint:false, so the safety profile is clear. The description reinforces this but does not go deeper into details like caching behavior (force_refresh parameter is only in schema) or output structure—adequate but not exceptional.

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?

The description is concise (two sentences plus a usage note) and front-loaded with the primary action. Every sentence contributes: first sentence defines the core purpose, second details outputs, third gives usage guidance, fourth notes integration. No wasted words, though it could be slightly more compact by merging the last two sentences.

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?

Given that the output schema exists and annotations are rich (readOnly, idempotent, non-destructive), the description covers all essential aspects: what the tool does, what it returns, when to use it, and its audit context. No missing information that would hinder an AI agent's ability to select and invoke this tool correctly among 70+ sibling tools.

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 the baseline is 3. The description does not add any parameter-specific details—it focuses on the tool's overall purpose. Since the schema already describes all three parameters (domain, format, force_refresh) and their roles are standard, the description adds no extra semantic value. An example of format values or the effect of force_refresh would improve this.

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 clearly states the tool's purpose: 'Look up and validate the SPF record for a domain.' It specifies the verb (look up/validate), resource (SPF record) and domain context. It distinguishes itself from siblings like 'resolve_spf_chain' and 'check_dmarc' by being focused on SPF validation, listing authorized senders, and flagging syntax errors.

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 'Use when you need to know who is permitted to send email as a domain' and notes it is 'Part of the scan_domain audit.' This provides clear context for when to use the tool, but it does not explicitly state when NOT to use it or mention alternatives (e.g., resolve_spf_chain for detailed chain resolution). Lack of exclusions keeps it from a 5.

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