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

Annotations already declare readOnlyHint=true, openWorldHint=true, and destructiveHint=false, so the safety profile is covered. The description adds genuinely new information beyond that: the operation hits live DNS and consumes 10 credits, which matters for tool selection. It stops short of saying what happens when a domain has no SPF record or when the record is malformed.

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 well-formed sentence with the tool name and core action front-loaded and the credit cost parenthesized at the end where it does not obstruct scanning. No filler or repetition. The redundant restating of the name at the start of the sentence is the only minor waste.

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?

The tool is simple (2 params, one required) and an output schema exists, so return values need not be described. The description covers what is checked, the optional IP test, network behavior, and cost. Only the no-SPF-record / invalid-record outcome is unaddressed, a small gap for a validator.

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 schema already documents both parameters with examples, establishing a baseline of 3. The description clarifies that the IP check is optional and describes it as an authorization test rather than a plain lookup, which adds slight meaning, but supplies no format or edge-case detail beyond the schema.

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 resource: checks the SPF DNS record for a domain and optionally tests an IP's authorization to send mail. That is far more specific than the title alone. It does not, however, distinguish itself from other DNS/email-auth siblings like DKIMValidator, DMARCValidator, or DNSSECChecker, leaving the agent to infer the boundary from the name.

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 rather than stated: the description makes clear you supply a domain to validate an SPF record and optionally an IP to test authorization. There is no explicit when-to-use versus DKIMValidator/DMARCValidator guidance and no stated preconditions (e.g., domain must exist). The credit cost note is a helpful practical cue for deciding whether to call it.

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