Email security grade

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

Annotations already declare readOnly/openWorld/idempotent/non-destructive, and the description adds meaningful traits beyond them: it uses live DNS, the only HTTP egress is the MTA-STS policy fetch at mta-sts.<domain>, and DKIM checks are limited to common selectors producing potential false negatives. This is exactly the context an agent needs to interpret results correctly.

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 purpose and output, then checks performed, then the routing hint, then caveats — no filler sentences. Each clause carries distinct operational value.

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?

With no output schema, the description still conveys the return shape (a letter grade plus a list of issues to fix), the checks covered, the data sources, and the known blind spot. Nothing material is missing for correct invocation.

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 100%, so the baseline is 3; the description goes further by explaining why dkim_selectors matters and why the default is incomplete ('only common ones are tried'), plus that the domain input tolerates a full URL. Minor credit above baseline, though most parameter detail already lives in 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+resource+output shape ('Grade (A-F) how well a domain is protected against being spoofed') and enumerates exactly what is checked (SPF, DMARC, MTA-STS, TLS-RPT, MX, DKIM). It explicitly distinguishes itself from the sibling dns_lookup, so an agent can route without opening either schema.

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?

Directly names the alternative and the condition for choosing this tool: 'Prefer this over reading TXT records with dns_lookup, it parses and grades them.' It also flags an important limitation (DKIM selectors can't be listed, so absence of DKIM is not proof of absence), which guides correct interpretation of results.

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