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

Annotations declare a non-read-only, non-destructive, closed-world write, and the description adds real context beyond that: a new test is created on every call (non-idempotent), an expiry window applies, and the user must act externally before it lapses. It stops short of saying what happens if the message arrives after expiry or whether tests can be re-read after expiration, so a 4 rather than 5.

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 the core action, then the return values, then the workflow and exclusions; every sentence carries distinct information. Slightly long at five sentences, but no sentence is pure filler, so it sits just below ideal brevity.

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 carries the return contract ('a test ID, unique recipient address and expiry time') and explains the external action needed to make the test meaningful. For a one-parameter, closed-world tool, nothing an agent needs to invoke it correctly is missing.

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% for the single parameter, so the schema already documents expected_from_domain with an example. The description only restates it as 'an optional expected sender domain', adding no format, matching, or validation detail beyond the schema baseline.

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 and resource ('Create an email-receipt test in MailVakt') and goes further to say what it explicitly is not ('Does not send email or measure inbox-versus-spam placement at Gmail, Outlook'), which separates it from the diagnostics siblings like diagnose_domain and analyze_email_headers. The follow-up read path via get_inbox_test is named, so an agent can distinguish it from its sibling without opening a 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?

Gives the full when-to-use workflow: call this to create the test, send a message to the returned address before expiry, then call get_inbox_test for the result. It also supplies the when-not ('does not send email or measure inbox-versus-spam placement'), leaving nothing to inference.

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