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

Annotations already declare readOnlyHint, idempotentHint, openWorldHint, and non-destructive behavior, so the description only needs to add relevant context beyond safety. It does so by explaining that the output is a payment requirements artifact tied to a signature usable in a later purchase step. This is useful sequencing and downstream-context information.

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?

The description is compact and front-loaded with the core purpose before the workflow note. Every sentence contributes meaningful information with no filler or redundant restatement.

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?

The combination of tool description, full schema coverage, annotations, and no required parameters provides enough guidance for an agent to call and use this tool correctly. The output schema likely covers return shape, and the description covers the important integration step.

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?

The input schema has 100% parameter description coverage and documents both parameters clearly. The description adds general context about credit packs but does not add meaning beyond the schema, so the baseline score of 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?

The description uses a specific verb and resource: 'Build x402 payment requirements to buy a pack of per-use MCP tool credits.' It clearly identifies the tool's purpose and differentiates it from the pro-related commerce tools by specifying credits, and it names the follow-up purchase tool.

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?

The description gives clear context for when to use this tool, namely as the first step toward purchasing credits. It also provides a workflow: build requirements, pay them, then call commerce.purchase_credits with the signature. It does not explicitly exclude alternatives like commerce.pro_requirements, but the credit-specific language makes the use case clear.

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