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

Annotations already cover readOnly, idempotent, openWorld, and non-destructive. The description adds context annotations do not: the call is free and consumes no credits, and it requires a BYOK key. It does not describe what fields the balance response contains, which is a minor gap for a read-only diagnostic.

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?

Front-loaded with the core purpose and free-status, then the usage triggers, then the key requirement and example. Efficient overall, though the inline example is somewhat redundant given the schema example block.

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?

No output schema exists, but the description names what is checked (balance, plan, status) and the error it diagnoses, which is enough for an agent to call it correctly. Slightly short on the shape of the returned balance data, but adequate for a single-parameter diagnostic 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?

Schema coverage is 100%, so the _apiKey parameter and its source URL are already documented. The description reinforces the BYOK requirement with the shipped-key caveat and provides a concrete call example, adding slight value over the schema baseline.

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?

Names a specific verb (Check) and resource (credit balance, plan, status) for the Revternal API key, and immediately distinguishes itself from siblings by stating it is free and consumes no credits. An agent can tell what it returns and how it differs from the revternal_* work tools without opening another schema.

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?

Explicitly states when to use it: before a bulk search/enrichment run to confirm credits, or to diagnose an HTTP 402 from another revternal_* tool. This names both the proactive and reactive trigger conditions, leaving nothing to inference.

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