modify_labels

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

Beyond annotations, the description discloses side effects ('changes the thread's labels'), the auto-creation of labels in 'add', the ignoring of unknown names in 'remove', and reversibility via inverse call. This adds meaningful behavioral context not present in the idempotentHint or readOnlyHint 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 description is tightly written with front-loaded purpose and structured segments (USE WHEN, DO NOT USE, SIDE EFFECTS). Every sentence conveys needed information without fluff, making it easy for an agent to parse quickly.

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?

Given the tool's simple scope (single thread labels) and the presence of an output schema, the description covers all essential usage aspects: operation semantics, edge cases (unknown labels), side effects, and reversibility. It is complete enough to guide correct invocation without requiring external knowledge.

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 0%, so the description must bear the full weight of parameter explanation. It does so by explaining that labels can be given by name or id, describing the special INBOX/UNREAD mapping, and clarifying the behavior of unknown names in each array. This goes well beyond the bare 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?

The description opens with 'Add/remove labels on a thread,' a specific verb and resource. It distinguishes itself from siblings by explicitly mapping archive to removing 'INBOX' and mark read to removing 'UNREAD,' and by pointing out that dedicated tools exist for simpler operations.

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 provides explicit 'USE WHEN' and 'DO NOT USE' guidance, naming alternatives ('dedicated tools') for plain archive/read/unread. This clearly tells an agent when to select this tool over similar ones like mark_read or archive.

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