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

Annotations indicate this is not read-only, and the description adds useful rail-specific behavior beyond annotations: defaults, invoice being 'coming_soon', and bank_card being 'handoff-only'. It stops short of detailing side effects of the enable action, but the bar is appropriately lowered by the presence of annotations.

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, front-loads the action, and packs the important rail caveats into a few short clauses. There is no filler or repetition of schema information.

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 the output schema exists and the annotations are present, the description covers the critical domain context around rail availability and handoff behavior. A small gap is the lack of explicit guidance about when to prefer sibling tools, but the description plus schema is sufficient for correct invocation in most cases.

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% and parameter descriptions are already solid. The description adds meaningful value for the `rail` parameter by explaining default rails, statuses, and special handling, which helps an agent know which values are actually usable beyond raw enum constraints.

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 specific verbs ('List or enable') and a specific resource ('agent payment methods'), clearly differentiating this from siblings like payment_mandate. The parenthetical '(action=list|enable)' reinforces the exact operations without restating the tool name.

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 implies usage for managing agent payment methods and clarifies the two actions, but it does not explicitly contrast with sibling tools such as payment_mandate or say when not to use this tool. Schema-level descriptions help, but the tool description itself offers no direct routing guidance.

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