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

Annotations already declare readOnlyHint=true, destructiveHint=false, openWorldHint=false, so safety is covered. The description adds one genuinely useful behavioral fact — that lookup terms are counted against the limit of 10 — but says nothing about whether an over-limit result is an error, a warning, or just a count, and nothing about return shape (no output schema exists).

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?

A single tight sentence with the core operation front-loaded and the lookup-count behavior appended. No filler, no repetition of 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 7-parameter tool with zero schema descriptions and no output schema, the description is too thin: it omits two parameters outright and gives no indication of what is returned (a record string? a term count? warnings?). Adequate to understand the purpose, insufficient to invoke confidently across the full parameter 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 0%, so the description carries the burden. It maps to five of seven parameters (ipv4/ipv6 as 'IP ranges', includes, useA/useMx as 'a and mx mechanisms') but leaves allQualifier (an enum with four values and a default) and redirectDomain entirely unexplained, including what the qualifier enum means for the generated record.

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?

A specific verb-plus-resource: 'Assemble an SPF record' from named inputs (IP ranges, includes, a/mx mechanisms), plus a secondary function (counting DNS lookup terms). It implicitly separates itself from the sibling check_spf (build vs. check), but never names the alternative, so sibling differentiation is only inferable.

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 — you call it when you want to construct a record — but there is no explicit when-to-use, when-not-to-use, or pointer to check_spf for validating an existing record. The mention of the lookup limit of 10 hints at the tool's purpose (producing compliant records) without stating a routing rule.

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