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

Goes beyond the annotations by asserting the operation is reversible, sends no messages and deletes nothing, and documents the idempotent outcome ('rien ne change et la réponse le dit (already_in_state)'). This meaningfully reinforces and extends the idempotentHint/destructiveHint metadata.

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?

Short, front-loaded with the action, then the behavioral caveats. Every sentence carries information; minor redundancy between 'réversible' and 'ne supprime rien' but nothing wasteful.

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?

No output schema exists, and the description compensates by describing the response signal (`already_in_state`) and the required write scope. For a one-parameter idempotent flag tool, this is sufficient to call it correctly.

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% for the single `conversation_id` parameter, so the schema already carries the semantics. The description adds no format or constraint detail beyond it, so baseline 3 applies.

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 ('Marque la conversation comme lue') and clarifies the semantics by likening it to opening the thread in the UI. It doesn't explicitly name the sibling `mark_conversation_unread`, though the counterpart relationship is obvious from the name.

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?

Usage is implied ('comme l'ouverture dans l'interface') and a prerequisite is stated ('Portée « write » requise'), but there is no explicit when-to-use / when-not-to-use guidance or reference to an alternative tool.

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