get_message

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

Annotations already declare readOnly/idempotent/non-destructive, and the description adds genuinely non-obvious behavior: the body is truncated at maxChars and the truncation is reported, HTML is converted to text, and attachment parts are summarized. The prompt-injection warning with the exact delimiters (⟦mail:ID …⟧) is exactly the kind of safety context an agent cannot get from structured fields.

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?

Front-loaded with the core action and return shape, then the truncation caveat, then the sibling pointer, then security, then args. Every sentence carries information, though the parenthetical field list ("part_id, name, type, size") and the parenthetical cut note are slightly denser than needed given an output schema exists.

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 2-parameter read tool with an output schema, this covers everything: what is returned, how the body is transformed and truncated, the default and bounds, how to get a messageId, when to prefer get_thread, and the untrusted-content framing. Nothing an agent needs to invoke it correctly 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 coverage is 0%, so the description carries the full burden and does: messageId's provenance is given, and maxChars gets a concrete valid range (200 to 100,000) plus the non-obvious default (8,090) that the schema only shows as 8090 with no explanation. This fully compensates for the undocumented schema.

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") and immediately enumerates what comes back: headers, HTML-converted body text, attachment metadata. It is clearly distinguished from the sibling get_thread, which handles whole conversations.

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 routes the agent: "For a whole conversation: get_thread." It also ties the required messageId back to the tools that produce it (search_threads, get_thread), so the agent knows the call chain and when this tool is the right terminal step.

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