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

Annotations already cover readOnly, idempotent, open-world, and non-destructive. The description adds real behavioral substance beyond them by naming the specific validation criteria applied (existence, validity, 10-lookup cap, all mechanism), which tells the agent what a 'pass' actually checks.

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?

One sentence, front-loaded with the action and resource, and dense with the enumerated checks. No filler, no redundancy with the title.

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?

For a simple read-only check with full annotation coverage and a fully documented schema, the description is nearly complete. It does not describe the shape of the result (e.g., pass/fail plus diagnostics), and with no output schema present that is a small remaining gap.

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 coverage is 100% and the schema already documents that a URL or email address is accepted, so the description adds no extra meaning about the single domain parameter. Baseline 3 for a fully documented single param.

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 resource (a domain's SPF record), then enumerates the exact facets examined: existence, validity, the 10 DNS lookup limit, and the all mechanism. The record type naturally distinguishes it from siblings like check_dkim, check_dmarc, and check_bimi.

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?

Usage is implied by the described checks — an agent can infer this is for validating an existing SPF setup — but there is no explicit when-to-use guidance and no mention of the alternative generate_spf_record, nor any exclusions or prerequisites.

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