check_spf

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

Even though annotations already declare readOnlyHint, idempotentHint, and destructiveHint, the description adds critical behavioral context: it explicitly says 'No auth, no side effects' and describes the recursive walk behavior and the counting against RFC-7208 limit. This goes beyond annotations, providing operational details like the 10-lookup limit and return of flattening guidance when near the limit.

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?

The description is concise and well-structured: two sentences that front-load the purpose, then list outputs and usage guidance. It packs a lot of information without redundancy, and every sentence earns its place. It avoids fluff and is easy to scan, which is ideal for AI parsing.

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?

Given the tool's moderate complexity (recursive walks, count limits), the description fully covers what the tool does, what it returns, and when to use it. With a single parameter fully defined in the schema, and annotations covering safety, the description is complete. No output schema exists, but the description enumerates key outputs ('parsed mechanisms, lookup graph, total count, qualifier, warnings'), so the agent knows what to expect.

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?

The schema already provides 100% coverage for the single parameter 'domain' with a clear description and maxLength. The description reinforces that the input is a domain only, but doesn't add new syntax details beyond the schema. Since schema coverage is high, a score of 4 is appropriate; it doesn't need to repeat parameter details but could add examples or edge cases.

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 clearly states it performs 'read-only SPF parse and validation for a domain', with specific behaviors like recursively walking include/redirect mechanisms and counting DNS lookups. It explicitly distinguishes itself from sibling tools by mentioning check_email_security for broader overview, and other siblings like flatten_spf for flattening guidance. The verb 'check' plus resource 'SPF' is specific and unambiguous.

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?

The description provides explicit usage context: 'Use for SPF auditing or before adding new include: senders' and explicitly contrasts with 'check_email_security for the broader SPF+DKIM+DMARC overview'. This gives clear when-to-use and when-not-to-use guidance, naming an alternative tool, which is exemplary.

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