Change labels

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

Goes well beyond the annotations (readOnlyHint=false, idempotentHint=true, destructiveHint=false) by disclosing error behavior for unknown label names, the exact return payload (account plus added/removed label ids), and an explicit safety boundary: TRASH and SPAM are refused, so deletion and spam-marking are impossible. The connection prerequisite is also surfaced. Nothing here contradicts 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?

Front-loads the purpose, then use cases, then error/return behavior, with no filler. A couple of sentences are densely packed with semicolon-joined clauses, which slightly hurts scannability but every clause carries information.

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?

Although there is no output schema, the description names the return values, the failure modes, and the account prerequisite. For a 5-parameter mutation tool with all-optional params, an agent has everything needed to call it correctly and to know what it cannot do.

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 100%, so the baseline is 3, but the description adds real meaning the schema lacks: labels may be names in any case or ids from list_labels, and unknown names produce an error. It also implicitly explains the message_ids vs. thread_id choice. It does not cover edge cases such as passing both targeting parameters or empty add/remove.

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 pair and resource ('Add or remove labels') plus the two targeting modes (specific messages vs. every message of a thread). It is clearly distinguishable from siblings create_label and list_labels, which are named as complements rather than alternatives.

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?

Gives concrete when-to-use recipes mapped to intent: mark read = remove UNREAD, mark unread = add UNREAD, archive = remove INBOX, star = add STARRED, file mail = add a label. It also routes the agent to list_labels for ids and create_label for new labels, and states the prerequisite (account connected with --labels) with a fallback error hint.

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