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

Discloses that it requires an API key, is read-only, and explains the anti-fraud ladder behavior including the 24-hour hold and refusal above daily ceiling. The description adds context beyond the readOnlyHint annotation by detailing the hold behavior and error codes, which is not present in 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 detailed but every sentence adds value. It is front-loaded with purpose and usage, then explains behavior, errors, and follow-up actions. No redundant or filler sentences; it's dense but well-structured.

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 single-parameter tool, the description covers all needed aspects: purpose, usage timing, behavior, error handling, and interpretation of results. It explains what to do if the limit is insufficient and mentions that other refusal reasons exist. Nothing essential is missing.

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 schema already covers the parameter fully with pattern and description, giving 100% coverage. The description adds practical guidance like 'Send digits only — no dots, slashes or dashes' and warns it's not a validity check, which goes beyond the schema's basic format specification.

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 it returns how much a specific Brazilian taxpayer (CPF/CNPJ) can move via PIX charge right now, in cents. It also distinguishes itself from lunium_create_pix_charge by explaining it's a read-only pre-check, and mentions calling it before the charge tool.

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 says 'Call it before lunium_create_pix_charge whenever the payer is new or the amount is not trivial.' It also provides exclusions: 'Do not use it as a document-validity check' and 'do not read a high limit as approval.' This is clear when-to-use and when-not-to-use guidance.

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