check_domain

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

With no annotations, the description carries the full burden and does well: it declares the operation is live and read-only, enumerates what is checked, mentions actionable fix instructions, and discloses a 10-minute result cache. It stops short of stating auth/permission needs or any rate limits beyond caching.

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?

Three sentences, front-loaded with purpose, then capability detail, then routing guidance. Every sentence earns its place with no redundancy against 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?

For a two-parameter read-only diagnostic tool with no output schema, the description covers what is examined and that fix instructions are returned. Return structure is only lightly implied, but an agent has enough to call it 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?

Schema description coverage is 100% (domain format and optional DKIM selector are documented in the schema), so the baseline is 3. The description adds no parameter-level detail beyond 'any domain name'.

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 (inspect) and resource (DNS/deliverability health of a domain) and immediately clarifies scope with 'without adding it' and the listed checks (MX, SPF, DKIM, DMARC, blacklist, domain age). It is clearly distinguishable from add_domain and list_domains.

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?

Explicit USE THIS for arbitrary prospect/candidate domains without saving, and DO NOT use for configuring (add_domain) or viewing configured domains (list_domains). Both alternatives and their selecting conditions are named.

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