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

Annotations already declare this is a non-destructive, idempotent write, and the description adds the required 'messages:write' scope, which is genuinely useful auth context. However, it never explains what 'handled' actually changes (inbox state, visibility to other agents, reversibility) — real gaps for a mutation on up to 200 messages.

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 compact sentences with the purpose front-loaded and the auth requirement second. Nothing is wasted, though the brevity is partly the reason the behavioral detail is thin.

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?

A bulk mutation (1–200 messages) with no output schema, no annotations beyond hints, and two undocumented parameters needs more than two sentences. It omits what the operation does to message state, whether partial success is possible, and how the batch limit affects calling strategy.

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 only 33%: message_ids and workspace_id carry no descriptions, and only idempotency_key is documented in the schema. The description does not compensate at all — it says nothing about batch semantics, the 200-item cap, UUID format, or workspace scoping, so an agent gets no extra meaning beyond field names.

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+resource ('mark messages as handled') and pins the actor ('by the calling agent'), which separates it from read_messages and post_message. It stops short of naming explicit siblings, but the intent is unambiguous.

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 only implied: an agent can infer it should call this after it has processed messages. There is no statement of when not to call, no reference to read_messages as the natural predecessor, and no mention that acknowledgement is scoped to the calling agent only.

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