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

Annotations say readOnlyHint=false but idempotentHint=true and destructiveHint=false, which aligns with 'one allowance per caller' returning the same token without side effects. The description adds high-value context beyond annotations: no wallet, signature, account, or email required; no x402 payment; the exact value and approximate call count; and the non-refill behavior. It clarifies the stateful allowance semantics and downstream token use.

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?

It is front-loaded with the core value (free, first tool to call), then covers return value, usage, limits, and alternatives in four compact sentences. Every sentence adds unique information without repetition or fluff.

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-param, free tool with an output schema, the description covers purpose, usage, return value semantics (token and value), limitations (one allowance, no refill), and the alternative purchase path. It is complete enough for an agent to invoke and use it correctly.

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?

There are zero parameters, so baseline is 4. The description explains how to use the returned credit_token as an argument to paid tools, which is useful integration guidance beyond the empty schema. No parameter syntax is needed, but it could mention whether the token is passed as a string or object if relevant.

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 states a specific verb and resource: it grants free credit and returns a credit_token worth $0.10. It also distinguishes itself from siblings by naming itself as the first tool to call when another tool reports payment required, and explicitly contrasts with /credits/buy as the refill path.

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?

It gives explicit when-to-use guidance: call this first if any tool says payment is required. It also states when not to expect more: one allowance per caller, asking again returns the same token, and refills come from /credits/buy. This is precise routing.

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