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

Beyond the annotations (readOnlyHint=false, openWorldHint=true, destructiveHint=false), the description discloses meaningful behavioral semantics: reading marks messages as DELIVERED, acknowledgment is the only indicator of session-level read status, ack does not imply agreement or action, and agent messages never substitute for user approval. This adds substantial context that annotations alone do not provide.

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?

Every sentence earns its place: purpose, timing, delivery-vs-read meaning, semantic boundaries, and a safety caveat. The description is front-loaded with the tool's core action and keeps the explanation tight without filler.

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?

Given the output schema exists and the parameters are fully documented in the schema, the description covers everything needed for correct invocation: when to call, what to pass, what the acknowledgment semantically means, and an important caveat about agent messages. There is no material gap for an agent to call this tool 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?

The input schema already provides full descriptions for both parameters: agent_id is the same one used in agent_checkin, and message_ids are the IDs returned by agent_inbox. The description only repeats 'passing the message_id of each one', so it adds no meaning beyond the schema. With 100% schema coverage, the baseline of 3 is appropriate.

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?

The description opens with a specific verb and resource: it tells senders that the agent actually read messages from agent_inbox. It clearly distinguishes acknowledgment from delivery and from agreement/action, and it differentiates this tool from the inbox-reading sibling by explicitly stating what agent_ack alone accomplishes.

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 explicit timing guidance: call it right after reading messages, passing each message_id. It also clarifies the delivery-vs-read distinction and why this call is necessary. It does not name explicit alternatives or negative conditions, but the context is clear enough that an agent would know when to invoke it.

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