update_message_labels

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

Annotations already declare idempotent, non-destructive, and non-read-only, so the safety profile is covered. The description adds a genuinely non-obvious behavioral fact beyond that: moving a message between folders changes its id, and the new id is returned. It still omits what a folder move implies for permissions or concurrent access, keeping it short of a 5.

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?

Two sentences, zero waste, with the core purpose front-loaded and the id-mutation caveat immediately after. Every sentence earns its place.

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?

The single biggest gotcha (id changes on move) is captured, but there is no output schema and the description does not cover the remove path, the required messageId, or what the response looks like beyond the new id. Adequate but with clear gaps for a 3-parameter mutation tool.

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 only 33% and the description adds no parameter-level meaning at all — it does not explain messageId (required), removeLabelIds (fully undocumented anywhere), or the add/remove interaction. It relies entirely on the schema's addLabelIds prose, leaving an agent guessing about removal and the required id.

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: adds and/or removes labels on a message, explicitly combined 'in one call'. That is clear, but it never names the sibling tools (label_message / unlabel_message) it subsumes, so an agent must infer the distinction itself.

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?

'in one call' implies this is the tool to pick when both adding and removing are needed, but there is no explicit when/when-not guidance relative to label_message, unlabel_message, or label_thread, and no stated prerequisites.

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