Read an email

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

Beyond the readOnlyHint and openWorldHint annotations, the description discloses useful return-behavior details: HTML-only messages are converted to plain text, and long bodies are truncated with a marker rather than silently cut. This helps the agent set expectations about the content it will receive. It does not discuss error behavior or rate limits, but with read-only annotation coverage this is adequate.

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 short sentences front-load the core behavior and then add the only critical output caveat about body conversion and truncation. There is no filler, repetition, or unnecessary detail.

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?

With an output schema, 100% parameter coverage, and read-only annotations, the description covers the important behavioral caveats. A minor gap is the lack of an explicit pointer to download_attachment for attachment content, but the phrase 'attachment list' already distinguishes the tool from that sibling.

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 the parameters are already well documented. The description adds no parameter-specific meaning beyond confirming that body, headers, and attachment list are returned; therefore the baseline score of 3 applies.

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: 'Open one message and return its body, headers, and attachment list.' This clearly identifies the operation and distinguishes it from sibling tools like search_emails (finding messages) and download_attachment (fetching attachment bytes).

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 the intended flow: after search_emails returns a UID, open that message. The uid parameter description reinforces this by saying the UID comes from search_emails. However, the description itself does not explicitly list when not to use this tool or direct the agent to download_attachment for actual attachment content, so it stops short of a 5.

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