update_message_labels

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

Annotations (readOnlyHint=false, destructiveHint=false, idempotentHint=true) are complemented by detailed behavioral context: labels are additive, message stays in folder, strict vs idempotent behavior, error conditions for missing label on add, and silent no-op for remove. No contradiction.

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?

Description is moderately sized with three paragraphs, front-loaded with core action, then behavior, then caveat. Every sentence adds value. Minor room for conciseness but overall efficient.

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?

No output schema, but for a mutation tool, return value is less critical. Description covers behavior, error conditions, and important caveat. Considering the complexity and siblings, it is sufficiently complete for correct agent usage.

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 baseline is 3. Description adds meaning: explains label path format (full paths under Labels/), provides examples, and clarifies that UID must be paired with folder to avoid ambiguity.

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 clearly states the tool's purpose: 'Add or remove Proton labels on a message.' It distinguishes from siblings like bulk_update_labels (handles multiple messages) and move_message (moves folder). The additive nature and namespace are explicitly mentioned.

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 explicit when-to-use and when-not-to-use: adds are strict (must exist, else error), removes are idempotent (silent no-op). It advises creating labels first with 'create_label' and warns about the UID+folder pair caveat.

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