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

Annotations already mark readOnlyHint=true, so the read-only nature is known. The description adds value by specifying the authenticated-user requirement, the exact data returned (balance, usage, Stripe status), and that it is free to call. No contradictions 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 a single sentence, front-loaded with the verb and resource, and contains no filler. Every word adds meaning, earning a high score.

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 there are no parameters and no output schema, the description is sufficiently complete for a simple read-only balance check. It clearly lists what the user gets. It could mention response format, but that is not essential for such a straightforward tool.

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 tool has zero parameters, and schema description coverage is 100%. With no parameters, the baseline is 4, and the description correctly focuses on the return value rather than explaining non-existent parameters.

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 function with a specific verb 'Return' and the exact resource: 'the authenticated user's current credit balance, usage, and Stripe subscription status.' It fully distinguishes from siblings, none of which relate to credits.

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 when to use it (checking credits) and adds 'Free to call' as a usage hint. However, it does not explicitly mention alternatives or exclusions. Since no sibling tools cover this functionality, the lack of explicit alternatives is acceptable.

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