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

Annotations already indicate read-only, idempotent, and non-destructive behavior. The description adds valuable context: it is 'Free' and reads specific data types. No contradiction with annotations, and the description enhances understanding beyond the structured data.

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 sentences: first sentence describes the tool's core functionality, second provides a usage hint. Both sentences are purposeful and front-loaded, containing no redundant information.

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 read-only tool with one optional parameter and no output schema, the description is fairly complete: it covers the main purpose and gives usage context. However, it could be more complete by explaining the return format or what 'aggregated usage' entails.

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 has one parameter 'days' with clear constraints, but schema description coverage is 0% (no description in schema). The tool description does not mention the parameter 'days' at all, failing to add meaning beyond what the schema already conveys. With low coverage, the description must compensate, but it does not.

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 specific verb 'Read' and the resources involved: 'credit balance, today's allowance state, and aggregated usage'. It distinguishes itself from sibling tools like 'claim_checkout' and 'convert_recipe', which have different purposes.

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 explicitly advises 'use before a paid batch', providing clear guidance on when to invoke this tool. However, it does not mention when not to use it or suggest alternatives, which would elevate the score to 5.

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