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

Annotations already declare readOnlyHint=true and destructiveHint=false, and the description reinforces them while adding meaningful behavior: body is truncated, body text must never be invented, it reuses the Integrations hub connection, requires API key/OAuth, share tokens are blocked, and there is a cost. This goes well beyond 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 core purpose is front-loaded in the first sentence, and the rest is dense but relevant: return contents, connection reuse, read-only scope, hallucination guard, connection fallback, auth, restriction, and cost. A few details could be merged, but no sentence is wasted.

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 single-message read tool with rich annotations and an output schema, the description covers the essential operational context: how to obtain the id, what fields are returned, truncation behavior, auth requirements, connection setup, access restrictions, cost, and the critical guardrail against inventing body text. Nothing required for correct invocation is missing.

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% and both parameters are documented, so the baseline is 3. The description adds value by specifying that message_id comes from search_gmail and reinforcing that id is an alias, which helps the agent understand the relationship between the two parameters.

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?

States a specific verb and resource: 'Read one Gmail message by id from search_gmail.' It clearly differentiates from search_gmail by being the follow-up read step and lists the exact fields returned (subject, from, date, snippet, plain-text body).

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?

Explicitly ties usage to search_gmail: ids come from that tool. It also gives clear exclusions ('cannot send, archive, or delete'), notes share tokens cannot call it, and tells the agent what to do if Gmail is not connected. This gives strong 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.