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

Annotations only carry destructiveHint=true; the description adds real context the agent can't see elsewhere: this is a WRITE, it defers any charge until the customer pays, and it returns a payment url. It stops short of noting the idempotency/retry behavior, which stays buried in the schema.

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-loaded with the "WRITE:" marker and ending on the HTTP endpoint. Nothing is redundant or padded.

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 7-parameter write tool with no output schema, the description covers the mutation nature, the deferred charge, and the return value, with units clarified. Minor gaps remain around retry/idempotency semantics, though those are documented per-parameter in the schema.

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 schema already explains all seven parameters. The description reinforces the unit_amount convention with a concrete conversion example (SGD 12.50 = 1250), but adds no meaning beyond that baseline.

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 (create), resource (payment Checkout Session), and scope limit (ONE item), plus the return value (payment url). The create verb separates it cleanly from the get/list/expire/refund siblings without needing to name them.

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?

Implies usage through "It charges nothing until the customer pays at that url," which tells an agent this is the pre-payment step, but it never states when to choose this over siblings (e.g. multi-item flows, refunds) or any preconditions.

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