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

Annotations already declare readOnlyHint=true and idempotentHint=true, so the description does not need to repeat safety. It adds value by indicating the tool reports the rate and top-up links, and suggests handing those to the user when balance is low. This is useful behavioral guidance but not extensive. 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 a single sentence, free of filler, and front-loaded with the primary purpose. It packs several relevant details (balance, reserved, available, rate, top-up links) without excessive length.

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 zero-parameter tool with an output schema that presumably documents the return structure, the description is complete. It covers what the agent needs to know to call it and what to do with the results (hand top-up links to user). No gaps in calling or interpretation.

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, so there is nothing to document. The baseline for this case is 4, and the description adds no conflict. It focuses on output content rather than parameters, which 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 resource (credits) and enumerates specific aspects (balance, reserved, available, rate, top-up links). It is distinct from sibling top_up, which is for adding credits, and from other tools like get_run or list_projects. The verb is implicit but the noun phrase is precise.

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 it is used to check credit-related information, and the mention of 'hand to the user when the balance is short' gives a usage cue. However, it does not explicitly contrast with alternatives like top_up or state when not to use this tool. Why an agent would choose this over other tools is left to inference.

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