Pay: methods

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

Annotations already carry readOnlyHint=true and openWorldHint=false, so the trailing 'Read-only' only confirms them. The description adds genuine value beyond annotations by disclosing the returned fields (type, brand, last four digits, expiry) and explicitly negating two likely confusions about whose cards are listed.

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 core action, then scope exclusions, then the safety note. The final 'Read-only' sentence is largely redundant with readOnlyHint, a minor redundancy rather than a structural flaw.

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?

With zero parameters, no output schema, and annotations covering safety and openness, the description supplies enough: what is listed, whose cards, which fields, and what is excluded. Slightly more detail on ordering or limits would round it out, but nothing needed to call it 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?

The tool takes zero parameters, so there is nothing for the description to disambiguate; baseline 4 applies. It also implicitly confirms the tool is unfiltered and acts on the signed-in user's context rather than accepting an identity parameter.

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 ('List saved payment methods') and immediately narrows scope: cards saved by the signed-in user as a customer of this project, not end users' cards or the billing-account card. That scoping cleanly distinguishes it from siblings like pay_payment_options and pay_payments.

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 boundaries ('does not list your end users' cards or the card on your Anythink billing account') imply when this tool is the right one, but there is no explicit when-to-use instruction or named alternative for the cases it excludes. Usage is inferable rather than stated.

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