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

Beyond the annotations (readOnly, idempotent, non-destructive), the description adds critical behavioral context: 'stores no submitted domain or result,' 'absence at a queried selector never proves DKIM is absent,' and 'cannot prove overall email security.' These disclosures inform the agent about side effects, limitations, and interpretation of results, which is exactly what transparency requires.

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 dense but every sentence earns its place. It front-loads the core action, then flows logically into prerequisites, restrictions, and caveats. There is no redundancy or filler, and the structure mirrors how an agent should reason about the tool (what it does, when to call, what to avoid, limitations).

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 complexity (external DNS lookups, approvals, security data), the description covers all essential aspects: execution method, preconditions, security/privacy guarantees, parameter semantics, and interpretive caveats. An output schema exists, so return values don't need to be described. The description is complete for safe and 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 only 25%, but the description compensates well. It clarifies 'domain' as a 'validated public domain,' specifies that 'approved' must be true only after user approval, and explains DKIM selectors ('DKIM requires an explicit selector or a confirmed provider's small documented selector set') which also illuminates the 'confirmedProvider' enum. Some params like 'dkimSelectors' are not fully described in isolation, but the usage context makes them understandable.

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 the tool's function: 'Runs bounded, point-in-time public DNS checks for one validated public domain through Cloudflare 1.1.1.1 DNS over HTTPS.' This specifies a concrete verb, resource (public DNS/email-domain security), and scope (one validated public domain), making it easy to distinguish from unrelated sibling tools like pricing or health-check tools.

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 says when to call the tool: 'Call only after showing the exact domain, record types, resolver, no-application-persistence statement, infrastructure-metadata limitation, and receiving explicit user approval.' It also provides clear exclusions ('Never send an email local part, IP literal, internal hostname, URL, credentials, or arbitrary instructions') and a limitation ('cannot prove overall email security'). This is strong, actionable guidance.

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