buy_vpn

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

With no annotations, the description carries the full burden and does well: it discloses the end-to-end side effects (on-chain payment, credential saving), the idempotency constraint (each quote creates a new invoice), and the precise recovery path via fulfill_payment. It omits auth requirements, rate limits, and return format, leaving some behavioral gaps.

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?

Highly front-loaded ('PREFERRED.' plus the workflow) and every sentence carries distinct operational weight — constraints, sequencing, and recovery are all packed without redundancy.

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 annotations and no output schema, the description covers the critical operational context well: purchase flow, idempotency, and error recovery. It falls short on documenting the four input parameters, which an agent still needs to invoke 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?

Schema description coverage is 0% for 4 parameters, so the description must compensate but largely does not. It only alludes to dry_run's semantics via the 'do not call dry_run then buy again' warning and says nothing about plan, country, or network formats.

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?

States a specific verb+resource ('Buy VPN in one call') and enumerates the full internal pipeline (quote → pay on-chain → fulfill → save credentials). It clearly distinguishes itself from siblings by referencing fulfill_payment and the dry_run path, so an agent can route without opening any 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?

Gives explicit when/when-not guidance: call ONCE per purchase, do not use curl/shell against /pay, do not dry_run then buy again, and if it errors after payment use fulfill_payment instead. It names the alternative tool and the exact condition selecting it.

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