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

Annotations already declare readOnlyHint=true, idempotentHint=true, openWorldHint=true and destructiveHint=false, so safety and idempotency are covered. The description adds real value on top by disclosing what is returned — the live record, a pass/fail status, and a fix suggestion — confirming a live external lookup rather than a cached or local check.

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?

Two tight sentences: the first front-loads the usage triggers, the second enumerates the return values. No repetition of the name/title and 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?

There is no output schema, but the description compensates by describing the three returned artifacts, and annotations cover the safety profile. For a single-parameter, read-only diagnostic this is fully sufficient for an agent to call it correctly.

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?

Only one parameter exists, and schema description coverage is 100% with an example (example.com), so the schema fully documents it. The description adds no additional format or edge-case guidance (e.g., subdomains, domains without SPF), so the baseline 3 is appropriate.

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 names a specific resource (the domain's SPF record) and the exact outcomes checked — validity, which servers may send for the domain, and why SPF fails. This makes it trivially distinguishable from parallel siblings like dmarc_check, dkim_check, and especially spf_generate, since it operates on a live record rather than producing one.

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?

It gives an explicit when-to-use clause keyed to user intents ('asks whether a domain's SPF record is valid', 'which servers may send email', 'why SPF fails'). It stops short of naming an alternative tool or stating when NOT to use it (e.g., use spf_generate to create a record instead).

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