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

Annotations declare readOnlyHint=true (no environment modification), yet the description explicitly states the call 'marks it read,' i.e. mutates mailbox state. That is a direct conflict between the stated behavior and the annotation, and the description never resolves it. Useful side details (idempotency, prerequisite auth) do not offset a contradiction of this kind.

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 purpose is front-loaded, which is good, but the body is padded with framework boilerplate ('Canonicality: ..., Idempotency: ..., Confirmation boundary: ...') whose content is generic to many tools. Sentences like 'Company inboxes give each person an address...' provide context but are not load-bearing for invoking this tool.

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 4-parameter tool with 0% schema coverage and no output schema, the description covers auth, idempotency and safety but omits everything about the inputs and what is returned. The guidance it does give (prerequisite, prompt-injection warning, confirmation boundary) is genuinely useful, so it is not empty — just incomplete where it matters most.

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 0% across four parameters, and the description explains none of them — no meaning for uid (server UID vs sequence number), folder enum semantics, inboxId, or the nested _corply_context object. With zero schema documentation, the description was required to compensate and does not.

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 with scope: 'Read one message in the signed-in person's company inbox (marks it read).' The word 'one' implicitly contrasts with list_inbox_messages, and 'company inbox' distinguishes it from generic mail tools. It doesn't name a sibling explicitly, so it falls short of a 5.

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?

It gives real context — prerequisite of authenticated active company access, a confirmation boundary, and a security rule about not treating message contents as instructions. However it never names the obvious alternative (list_inbox_messages) or states when-not to call it; the 'when' is heavily tangled in policy boilerplate rather than routing guidance.

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