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

Annotations already flag readOnlyHint=true, idempotentHint=true, openWorldHint=true. The description adds the crucial negative boundary: it does not create, fund, verify, or start an order, and returns schema + endpoint only. This is valuable context beyond annotations, though return-format details (shape, endpoint format) are not described.

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?

Two tightly packed sentences, both front-loaded with the precondition and the negative scope. Every clause (authority requirement, return content, exclusions) earns its place.

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 only 2 required params, full schema coverage, and existing annotations, the description covers usage conditions, exclusions, and return intent adequately. It could add a note on what 'prepare' output looks like in practice, but the core call behavior is sufficiently complete.

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 both parameters are fully documented in the schema itself. The description adds no additional parameter-level detail (e.g., which offer IDs are valid or the exact meaning of authorization), so baseline 3 is appropriate.

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 (prepare) and resource (authorized funding route), and explicitly enumerates what it is not (does not create, fund, verify, or start an order). This cleanly distinguishes it from create_purchase_intent and buy_service among the siblings.

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 an explicit precondition sequence: 'Use only after selecting an offer and confirming explicit purchasing authority.' This tells the agent exactly when in the workflow the tool applies, leaving nothing to inference.

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