Add pull request labels

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

Annotations already provide idempotentHint=true and destructiveHint=false, but the description adds a specific non-destructive behavior: 'Existing labels are preserved.' This clarifies that labels are added, not replaced, a key behavioral detail beyond the generic annotations. No contradiction with 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 two sentences, front-loaded with the action, and every sentence earns its place. The second sentence conveys an important behavioral nuance without waste.

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 simple mutation tool with annotations and a clear description, the information is nearly complete. It lacks details about response format or error handling, but given the straightforward nature and the presence of annotations, it is adequately 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?

The input schema covers 100% of parameters with meaningful descriptions (owner, repo, pull_number, labels). The description does not add parameter-level semantics beyond what the schema already provides, so the baseline of 3 applies.

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 action ('Add one or more labels to a pull request') with a specific verb and resource. It distinguishes from sibling tools (which read PRs, comment, review) by focusing on label modification, and adds a behavior note ('Existing labels are preserved') that further clarifies scope.

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 implies usage when labels need to be added to a PR, but gives no explicit guidance on when not to use it or alternatives. There are no exclusions or comparisons with sibling tools, so usage context is merely implied rather than stated.

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