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

Annotations only carry the safety profile (destructiveHint=true, openWorldHint=true, idempotentHint=false); the description adds the non-obvious behavior that the message bypasses its own targeting rules, appears exactly once, and is excluded from stats. It does not state the prerequisite state (message must exist/be published, widget installed), and the 'never counting in stats' framing sits in mild tension with destructiveHint=true, though it does not directly contradict it.

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, no filler, with the mechanism front-loaded and the usage constraint second. Every clause carries information.

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 destructive, open-world mutation tool with no output schema, the description covers what happens on invocation and who to target, and the schema's confirm parameter covers the human-approval gate. Missing only prerequisites and the fact that the visitor's state is altered by the test.

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%, so the baseline is 3, but the description adds a real constraint beyond the schema: the email should be the caller's own and the caller must be signed in to the site. It adds nothing about messageId beyond what the schema already says.

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 plus the exact delivery mechanism: the saved message is shown once to the visitor with that email on their next site visit. That mechanism (rule-skipping, stat-exempt, next-visit delivery) implicitly separates it from siblings like send_test_email and test_journey, which deliver by other means.

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 a clear usage constraint — target your own email and be signed in to your own site — which tells the agent who the test subject should be. It stops short of naming when not to use it or pointing at alternatives such as send_test_email or test_journey.

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