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

Beyond the annotations (readOnlyHint, idempotentHint, destructiveHint), the description adds valuable behavioral details: it confirms the tool is read-only and idempotent, and explicitly describes the error behavior (returns an error object instead of raising protocol errors). This aligns with and enriches the annotations without 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?

The description is concise and well-structured: it opens with a clear purpose, includes a representative example, covers usage boundaries, and explains error handling—all in a few sentences. Every sentence adds necessary information without redundancy.

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?

Given the tool's simplicity (3 parameters, 1 required, output schema exists), the description covers all essential aspects: purpose, input example, usage guidelines, behavioral guarantees (read-only, idempotent), and error handling. It is fully sufficient for an agent to use this tool correctly.

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 already has 100% description coverage for all three parameters, so the baseline is 3. The description adds value by providing a typical example input and output, which helps the agent understand how parameters map to behavior. It also mentions error handling that references parameter constraints. However, it does not add new parameter-level details beyond what the schema provides, so a 4 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?

The description clearly states the tool's purpose with a specific verb+resource ('Compute the tip and per-person split for a bill') and provides a concrete example. It explicitly distinguishes this tool from the sibling 'budget_split' by stating when not to use it, making the purpose unambiguous.

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 gives explicit guidance on when to use the tool ('Use for one bill shared among a group') and when not to use it ('Not for recurring household budgeting'), naming the alternative sibling tool 'budget_split'. It also explains error handling and retry safety, providing complete usage context.

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