update_message_labels

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

Beyond the single annotation (destructiveHint: false), description details that adding copies the message, removing finds and expunges, and the message stays in its source folder. Also explains the optional prefix handling. This fully covers the behavioral traits.

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?

Three sentences are concise and front-loaded with the core purpose. The structure is logical, but could be slightly more organized with bullet points for the two actions. However, it is efficient and clear.

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 mutation tool with 3 parameters and no output schema, the description covers the essential behavior, prerequisites, and parameter specifics. It does not mention return values, which is acceptable. Overall, it is nearly complete.

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%, with each parameter well-described. The description adds no new parameter information beyond stating the label namespace and the prefix handling, which is already in the schema. Baseline 3 is appropriate.

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?

Clearly states 'Add or remove Proton labels on a message without moving it', specifying verb and resource, and distinguishes from move operations. Differentiates from sibling tools like bulk_update_labels and move_email.

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 context on when to use (adding/removing labels without moving), warns that labels must be created first via create_folder, and explains the effect. Does not explicitly state when not to use, but implies alternatives like move_email for moving.

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