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

Annotations only declare readOnlyHint=false, openWorldHint=true, destructiveHint=false. The description goes well beyond this: it discloses that the call does not complete payment, that stripe needs a human to enter card details, that crypto returns a raw address an agent can pay autonomously, and that credits are added automatically after confirmation.

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?

Front-loaded with the key constraint ('does NOT complete a payment by itself') and organized into two scannable bullets per method. Slightly long, but nearly every sentence carries decision-relevant information for an autonomous agent.

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?

No output schema exists, so the description must explain returns — and it does precisely, naming checkout_url, the Plisio invoice, address and amount per method. Nothing an agent needs to call this correctly 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?

Schema coverage is 100%, so the baseline is 3, but the description adds real meaning beyond the schema: the autonomy implication of method='crypto' and the currency enum (raw wallet address, agent-payable). It stops short of adding format/syntax detail for the package id.

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 and resource ('Start a purchase of a credit package and return a way to pay') and immediately clarifies the boundary that it does not itself complete a payment. This distinguishes it from siblings like get_packages and get_credits.

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 tells the agent to call get_packages first for a package id, and gives a clear selection rule between methods ('Prefer crypto for fully autonomous top-ups'). It also states the when-not condition for stripe (requires a human browser).

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