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

Annotations only declare destructiveHint=true; the description carries substantial extra behavioral context beyond that: exact case-insensitive matching (never partial), refusal of system labels, the gmail.modify permission requirement, a reconnect hint for older accounts, and an explicit user-confirmation warning for destructive renames.

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?

Purpose is front-loaded in the first sentence with operational caveats following in a logical order. It is dense and slightly long for the payload, but each clause (matching rule, refusals, auth, confirmation) contributes distinct value.

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 no output schema and only a destructiveHint annotation, the description covers everything an agent needs: permissions, matching semantics, system-label exclusions, multi-account handling, and safety guidance. Nothing material is missing for correct invocation.

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 name, account, new_name, and both visibility enums. The description reinforces the exact-match lookup rule and account guidance, but adds little that isn't already in the schema, so the baseline 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?

States a specific verb (rename) plus resource (Gmail label) and the secondary capability (display/visibility settings) in the opening clause. This clearly separates it from create_label, delete_label, list_labels, and modify_message_labels without needing to open a 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?

Provides clear conditions: it operates on an existing label, refuses system labels (INBOX/STARRED/CATEGORY_*), needs gmail.modify, and requires `account` for multi-account setups. It also advises confirming before renaming a relied-upon label. It stops short of explicitly routing to a sibling (e.g., 'use create_label to make a new one'), so it's strong context rather than full alternative-mapping.

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