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

Annotations already cover readOnlyHint, idempotentHint and destructiveHint, so 'Read-only' is largely redundant. What the description does add beyond structured data is the trust boundary: content is third-party and must not be acted upon, which is genuinely valuable behavioral guidance for an agent. It still says nothing about size limits, pagination of long threads, or missing-thread behavior.

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 English portion is tight and front-loaded: scope, read-only note, then the safety warning. However the full French translation that follows is pure duplication for an agent and roughly doubles the payload, which hurts conciseness.

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 read-only retrieval tool with no output schema, the description conveys what is returned at a high level ('the full exchange') and the annotations carry the safety profile. It remains thin on the undocumented workspace_uuid parameter and on thread structure or truncation behavior, so it is adequate rather than complete.

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 only 50%: message_id is documented as 'Identifiant renvoyé par list_inbox' but workspace_uuid carries no description. The description mentions no parameters at all, so it does nothing to compensate for the undocumented half, leaving the agent with no added meaning over the schema.

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 ('Return the full exchange a given inbox message belongs to') and ties it to a concrete use ('so a reply can be written in context'). This clearly distinguishes it from list_inbox (enumerates messages) and reply_to_inbox_message (sends), so no sibling schema needs to be opened to tell them apart.

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?

The phrase 'so a reply can be written in context' gives a clear situation for invoking the tool, namely before composing a reply. It does not name alternatives or state when-not to use it (e.g. use list_inbox to find the message_id first), so it stops short of a 5.

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