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

Annotations already declare readOnlyHint, idempotentHint, and destructiveHint, so the description's 'Read-only' is redundant. However, it adds the detail that the response includes extracted_text and attachment metadata, which gives some expectation of the output. No contradictions with annotations.

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 description is a single, clear sentence with no filler. It front-loads the action and includes the key output details.

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?

The tool is simple, but the description omits any explanation of the parameters or when to use it. There is no output schema, so the description's mention of extracted_text and attachment metadata helps, but it's not enough to fully guide an agent on how to correctly invoke the tool.

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 schema has zero description coverage for the two required parameters (inbox_id and message_id), and the description does not explain their meaning or format. The description adds no value in helping the agent understand what values to provide.

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 clearly states the action (fetch), the resource (one stored Cooper message), and specifies the included fields (extracted_text and attachment metadata). It distinguishes from list_messages by emphasizing 'one' and 'stored', making the purpose 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?

The description provides no guidance on when to use this tool versus siblings like cooper_list_messages or cooper_search. It doesn't mention that this tool requires specific IDs or that it's for retrieving a single message by ID. Without this, an agent might not know when to select it.

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