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

Annotations already declare readOnlyHint=true, idempotentHint=true, and destructiveHint=false. The description adds value beyond these by stating it is free, takes no input, reads the account behind the credential, never presents a payment challenge, and details the error case for anonymous callers. No contradiction with annotations. The extra context about permissions and error handling is helpful.

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 well-structured, starting with the key fact 'Free' and then the core purpose. It is about 3-4 sentences long, each sentence adding distinct value (balance, cost breakdown, usage guidance, error case). It is not overly verbose, but could be slightly tighter by removing redundant phrasing like 'connected to' and 'connected with'. Still, it is efficient and clear.

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 no output schema, the description fully explains what the tool returns: credit balance, credit worth, operation costs, monthly free allowance, and whether a card is on file. It also mentions the account page name for top-ups. The error case for anonymous callers is covered. The tool has no parameters and is simple, but the description leaves no gaps for an AI agent to understand its behavior and output.

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 description cannot add parameter-level meaning. According to guidelines, baseline is 4 for 0 params. The description correctly notes 'Takes no input: it reads the account behind the credential your client already connected with.' This is sufficient and does not repeat schema information.

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 reports the credit balance and related financial details (credit worth, operation costs, free allowance, card on file). It is a unique tool among siblings (convert_video, extract_frames, etc.) as it focuses on account balance and usage limits, not media processing. The verb 'reports' and resource 'credit balance' are specific and unambiguous.

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 calling this tool to find out how much work can be queued and to get the top-up link. It distinguishes between paid account holders (who have balance) and anonymous callers (who get unauthorized error). It does not explicitly name alternatives, but the context is clear and the sibling tools are unrelated (e.g., convert_video, get_job_status). The guidance is practical and sufficient for an AI agent to decide when to use it.

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