Register a custom domain for receiving test mail. Returns the DNS records (TXT challenge + MX) to publish; the domain accepts mail only after verify_domain passes.
| Name | Required | Description | Default |
|---|---|---|---|
| fqdn | Yes | The domain to receive test mail on, e.g. mail.example.com. The response carries the TXT + MX records to publish. |
Changes observed during successful MCP inspections.
Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
With no annotations, description carries full burden. It discloses return of DNS records and the verification dependency. Lacks auth or rate limit details, but is sufficient for a simple tool.
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?
Two sentences with no filler. Purpose is front-loaded. Every word serves a purpose.
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?
Single parameter, no output schema, yet description fully explains the tool's action, return, and lifecycle. Adequate for its simplicity.
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 covers 100% of parameters. Description adds value by explaining the response (TXT + MX records) and the requirement for verify_domain, exceeding baseline of 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?
Description clearly states 'Register a custom domain for receiving test mail', with specific verb and resource. It distinguishes from siblings like verify_domain by mentioning the prerequisite.
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?
Explicitly notes that domain accepts mail only after verify_domain passes, guiding when to use that tool. No explicit when-not or alternatives, but context is clear.
Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.