Read an email's body

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

Annotations already declare readOnlyHint=true, idempotentHint=true, and destructiveHint=false, so the safety profile is covered. The description adds valuable behavioral context beyond annotations: the fallback behavior from text/plain to HTML-stripped-to-text, the maxChars truncation behavior, and the security warning to treat content as untrusted third-party data. It doesn't describe pagination mechanics in detail, but the offset parameter description covers that. No contradiction 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?

Four sentences, each earning its place: the first states the core function and fallback, the second gives the use case and sibling distinction, the third explains truncation and pagination, and the fourth is a security warning. The most important information is front-loaded. No wasted words.

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 tool with full schema coverage, no output schema, and annotations covering safety, the description is complete. It covers what the tool returns (headers plus body), how it handles HTML fallback, how truncation works, how to get more content (offset/nextOffset), and the security posture. An agent has everything needed to select and invoke it correctly.

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 schema already documents all five parameters. The description adds meaning beyond the schema by explaining the fallback behavior ('falling back to the HTML part stripped to text') and the truncation semantics ('Long bodies are cut at maxChars: raise it or page through with offset'). It also clarifies the relationship between messageId and gmail_find_attachments. This goes beyond the baseline 3 for full schema 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 states a specific verb ('Read'), a specific resource ('one Gmail message in full'), and the exact scope (headers plus decoded text/plain body, falling back to HTML stripped to text). It also distinguishes itself from gmail_find_attachments, which only returns a ~200-character snippet, so an agent can tell them apart without opening the schema.

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 explicitly says when to use this tool ('This is how text that arrived by email ... becomes usable here') and names the alternative (gmail_find_attachments) with the condition that selects it (only returns a snippet). It also gives guidance on long bodies: raise maxChars or page through with offset. This is clear when-to-use and when-not-to-use guidance.

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