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

Annotations already declare readOnlyHint, idempotentHint, destructiveHint=false, and openWorldHint=false, so the safety profile is fully covered. The description adds the 'local' mode distinction but does not add auth, rate-limit, or return-behavior context beyond what annotations and the output schema 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?

Two tight sentences with the core retrieval action front-loaded. The parenthetical ID source and mode note are useful and do not waste space.

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 simple read tool with a full output schema and comprehensive annotations, the description supplies what the agent needs: what is fetched, how to source the ID, and the special meaning of 'local'. Return values and remaining parameter details are adequately covered by structured fields.

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 100%, so the baseline is 3, but the description adds meaning beyond the schema by explaining that 'local' refers to a message sent from this computer and by noting where the required ID can be obtained. The target_session parameter is left to the schema, which is acceptable given full coverage.

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 uses a specific verb and resource ('Get one scheduled WhatsApp message by its ID') and distinguishes it from list_scheduled_messages and send_message by emphasizing single-message retrieval by ID. An agent can immediately tell this is not a list or creation tool.

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 tells the agent where the ID comes from ('from list_scheduled_messages or send_message') and when to use mode 'local'. It does not explicitly exclude alternative tools like manage_scheduled_messages, but the retrieval context is clear.

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