Read a message

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

The description goes beyond the readOnlyHint annotation by explaining exactly how the message is processed: HTML to text, images/styling dropped, no external content fetched, truncation with a visible note, and untrusted content marking. This gives a complete safety and behavior profile.

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?

Three concise sentences, front-loaded with the core action, followed by important behavioral details. No redundancy or 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 tool lacks an output schema and has 4 parameters, the description covers the essential return behavior (readable text, truncation, untrusted marking) and relevant processing. It could benefit from mentioning what other fields are returned (e.g., subject), but the current coverage is solid for an agent's decision-making.

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 100%, so parameters are already fully documented. The description adds useful context about long-body truncation that relates to maxChars and textOffset, but it doesn't add meaning to each parameter individually. Baseline 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 clearly states 'Reads one message by its id and returns it as readable text,' specifying the verb, resource, and selection method. This distinguishes it from sibling tools like list_messages and search_messages, which operate on collections.

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 implies usage when you already have a message id, and the schema reinforces this by noting the id comes from list_messages or search. It doesn't explicitly compare against alternatives, but the context is clear enough for an agent to infer when to use this tool.

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