l402-buy-credits

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

Annotations already flag destructiveHint=true and openWorldHint=true, so the safety profile is handled. The description adds the mode behavior and the toll-booth restriction, but it does not clarify side effects of a purchase, such as spending funds, irreversibility, or error/response behavior.

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?

Three short sentences front-load the purpose and immediately state the key branching behavior. Minor redundancy exists between 'from a toll-booth server' and 'Only works with toll-booth servers,' but overall it is tight.

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 three-parameter tool with no nested objects, core invocation is covered: required URL, optional method, optional amountSats, and the toll-booth constraint. However, there is no output schema and the description does not say what a successful purchase or tier-discovery response contains, which is a notable gap for a financial operation.

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 description coverage is 100%, so the baseline is 3. The narrative about omitting/providing amountSats adds a little clarity, but it largely repeats the schema's description of amountSats and does not enrich method or url beyond what the schema already says.

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 opens with a specific action ('Buy credits') and identifies the resource ('a toll-booth server') and a differentiator ('volume discounts'). It distinguishes this from sibling payment tools by restricting it to toll-booth servers, though it never names a sibling explicitly.

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?

Provides explicit branching guidance: omit amountSats to discover tiers, provide amountSats to buy a specific tier, and only works with toll-booth servers. This gives clear when-to-use context, but it does not compare against siblings such as l402-pay or l402-discover, so it falls just short of a 5.

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