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

With no annotations, the description carries the full burden and largely succeeds: it discloses read scope (SPF lookup-limit counting and include following, DMARC policy/pct/reports and parent-domain inheritance, DKIM selector probing, MX-based provider detection) and the return shape. It omits operational traits like rate limits, failure modes, or timeout/caching behavior.

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?

One dense sentence, front-loaded with the agent-facing question, then the mechanism, then the output. No filler and no repetition of the schema.

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?

There is no output schema, and the description compensates by specifying the return (a protected/partial/unprotected verdict plus exact TXT records to add), so an agent knows what to expect. It is complete on inputs and outputs but silent on error handling and cost/latency, which a network-check tool could reasonably mention.

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 already 100%, so the baseline is 3, but the description adds real meaning: it explains that 'selector' is only needed when not probing common selectors, implying a fallback scan when omitted, and that 'domain' also accepts the DKIM-curated lookups for email addresses. That is value beyond the schema text.

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?

Opens with the exact question the tool answers ("Can someone fake (spoof) email from a domain?") and then names the specific resources it reads: SPF, DMARC, DKIM, MX. This distinguishes it cleanly from generic siblings like dns_lookup and check_dns_propagation.

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 framing makes the use case unambiguous — auditing a domain's email spoofability — which is clear context for selection. It stops short of naming alternatives or stating when-not to use it (e.g. for raw record retrieval), so it falls short of a 5.

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