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

Annotations already declare readOnlyHint=true, idempotentHint=true, and destructiveHint=false. The description adds valuable behavioral context beyond those: it states that the body is sanitized and truncated to a configured limit, and that the result includes an attachment list. This gives the agent a clearer picture of what the call will return without contradicting the 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, tightly written sentence that front-loads the core return contents first and appends the truncation caveat. Every phrase earns its place and there is no filler or repetition.

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 read-only, idempotent tool with simple parameters and no output schema, the description covers the essential return values and the truncation behavior. The main gap is the ambiguity of 'configured limit' versus the max_chars parameter, which could confuse an agent deciding how to control response size. Overall, though, the combination of description, schema, and annotations is sufficient for correct invocation in most cases.

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 80%, so the schema already documents most parameters. The description adds semantic value by explaining the truncation behavior, which gives meaning to max_chars and the 'configured limit' phrase. It doesn't fully explain the interaction between max_chars and the configured limit, but it goes beyond what the bare schema provides.

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 ('Returns') and names the exact resources delivered: headers, sanitized text body, and attachment list for one message. It clearly identifies the tool's scope as a single message reader, which is enough to distinguish it from siblings like get_attachment or get_thread even without naming them.

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 explicit guidance about when to use this tool versus alternatives such as get_thread, search_messages, or fetch. There is no mention of prerequisites, exclusions, or routing conditions. Usage is only weakly implied by the phrase 'of one message' and the schema's 'uid from search_messages' parameter, not by the description itself.

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