gmail_apply_labelAssign a label to selected Gmail messages, creating the label automatically if it does not exist. Simplify inbox triage by categorizing messages such as Newsletters or Receipts.
Apply a label to the given messages. The label is created if it does not exist yet (e.g. 'Newsletters', 'Receipts', 'To Review').
| Name | Required | Description | Default |
|---|---|---|---|
| ids | Yes | Message ids to label. | |
| label | Yes | Label name, e.g. 'Receipts'. |
Changes observed during successful MCP inspections.
v0.1.0Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
With no annotations, the description carries the full burden, and it does disclose one genuinely valuable behavior: the label is created if it does not exist. It still omits whether labels are additive or replace existing ones, permission/scope requirements, the 500-message cap behavior, and what the call returns (no output schema exists to cover that).
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 short sentences, zero filler, with the core action front-loaded and the side effect (auto-creation) immediately after. Every clause 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?
For a two-parameter mutation with no annotations and no output schema, the description covers the action and the auto-create side effect but leaves the agent guessing about mutability semantics (additive vs. replacing), auth scope, and the return value. Adequate but with real gaps given the absence of structured behavioral metadata.
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 100%, so both parameters are already documented in the schema; baseline is 3. The description adds only example label values ('Newsletters', 'Receipts', 'To Review'), which reinforces the label-name format but adds no constraint or semantics beyond the 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 states a specific verb and resource ('Apply a label to the given messages') and adds the non-obvious auto-creation behavior. It does not differentiate from the specialized sibling operations (gmail_star, gmail_archive, gmail_mark_read), which are all label-style mutations, so an agent gets no help choosing between the generic and the specialized tools.
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?
Usage is implied clearly by the verb and the mention of example labels, so an agent can infer when to reach for it. However, there is no explicit when-to-use statement, no exclusion, and no mention of the specialized siblings that might be preferable for system labels.
Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.