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

With no annotations, the description carries the full burden and does so well: it discloses the optional read of current SPF/MX, preservation of unknown entries, drop warnings, live lookup counting against the 10-lookup limit, and the contents of the response. The only gap is that it never explicitly says whether the record is published or merely returned, though 'Returns the record' strongly implies generation-only.

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?

Front-loaded with the purpose, then behavior, then return values. The long service-id list is verbose but justified because the schema defines no enums for `services`, so the ids exist nowhere else.

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 5-parameter, zero-required, no-output-schema, no-annotation tool, the description covers inputs, side effects, limits, and return contents including the starter DMARC record. Minor omissions (behavior when `domain` is absent, interaction between `services` and `includes`) keep it short of complete.

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 60% (domain and strict are documented there), and the description compensates for the undocumented ones: it enumerates the full set of valid service ids for `services`, explains that `ips` and `includes` add extra entries, and notes that `domain` triggers a read of the current record. That is meaningful added meaning beyond the bare array/string types.

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 and artifact: 'Build one valid SPF TXT record for a domain from the services that send its email.' That is clearly distinct from siblings like check_email_security or dns_lookup, which inspect rather than generate records.

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?

Gives clear operational context: feed it sending services, optionally let it read the existing SPF/MX, and it will warn before dropping unknown entries. It stops short of naming alternatives (e.g., check_email_security for auditing an existing record) or stating exclusions, so it is context-rich but not a full when/when-not guide.

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