check_spf

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

With no annotations, the description carries full burden. It discloses that the tool is read-only, recursively walks SPF mechanisms, counts DNS lookups against RFC limits, and returns specific outputs like parsed mechanisms and warnings. It could be slightly more explicit about error handling (e.g., missing SPF record), but overall it provides strong behavioral transparency.

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 (4 sentences) and front-loaded with the core purpose. Every sentence adds value: purpose, behavior, outputs, and usage guidance. No extraneous words or repetition.

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 simplicity of the tool (1 parameter, no output schema), the description covers input, behavior, outputs (parsed mechanisms, lookup graph, count, qualifier, warnings), and usage context. It is fully self-contained and informs the agent of everything needed to use the tool 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?

The schema has one parameter 'domain' with 100% coverage in its description ('Domain name, e.g. example.com'). The tool description does not add new semantics beyond this, as the schema already defines it clearly. Following the guidelines, baseline is 3.

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 defines the tool as 'Read-only SPF parse and validation for a domain,' specifying the verb (check/validate), resource (SPF record), and scope (a single domain). It distinguishes itself from the sibling tool 'check_email_security' by noting its narrower focus on SPF only.

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 explicitly states when to use this tool ('for SPF auditing or before adding new include: senders') and when to use an alternative ('use check_email_security for the broader SPF+DKIM+DMARC overview'). It also notes there is no auth required and no side effects, guiding the agent appropriately.

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