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

The description discloses PATCH semantics ('Only the fields you provide are changed'), which is key behavioral info. However, it does not mention permissions, rate limits, atomicity, or side effects. Since no annotations are provided, the description carries the burden; it is adequate but not thorough.

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 concise (three sentences), front-loaded with purpose, and each sentence adds necessary detail. There is no fluff or repetition.

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?

With 9 parameters, 1 required, and no output schema, the description covers the main workflow (update fields, use find_billing_work for id). However, it does not describe return values, error conditions, or constraints like the required project_id being valid. It is mostly complete for the primary use case but lacks some context.

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. The description adds value by explaining PATCH behavior and clarifying that billing_types 'Replaces the entire set — include all types you want to keep.' This goes beyond the schema, which simply says 'Comma-separated list.'

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 purpose: 'Update an existing billing project'. It specifies the resource (billing project) and verb (update), and distinguishes itself from sibling tools like create_project and delete_project by focusing on updating. The listing of updatable fields 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 provides explicit guidance: 'Discover ids with find_billing_work - never ask the user for an id.' This tells the agent to use a specific sibling tool to obtain the project_id, avoiding user prompts. It implies not to use this tool for creation (use create_project) but does not explicitly compare to other update tools among siblings.

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