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

Annotations already declare readOnlyHint and idempotentHint, covering the safety profile. The description adds value beyond annotations by noting the data is 'live' and providing sequencing guidance ('before naming a rail or currency'). This gives useful behavioral context about real-time data and expected call order.

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 sentences with no filler. The first sentence front-loads the return categories, and the second provides a clear usage directive. Every word 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?

The tool has only one optional parameter fully documented in the schema, and no output schema. The description enumerates the return categories and states when to call it. For a simple discovery tool with no required parameters, an agent has everything needed to invoke it correctly.

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 includeRelaySources parameter is already fully documented in the schema. The description does not add any additional parameter-level semantics. 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?

The description uses a specific verb ('Return') and enumerates a precise set of resources: 'live Base USDC destinations, payout platforms, fiat currencies, payee hints, amount bounds, and pricing.' This clearly differentiates it from sibling tools like peer_cash_source_capabilities or peer_config_currencies by the specific data it returns. The purpose is immediately understandable.

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 phrase 'Call this before naming a rail or currency' gives an explicit when-to-use directive. It conveys that this tool is a prerequisite for other operations that require selecting a rail or currency. It does not, however, name alternative tools or state when not to use it, so it stops short of a 5.

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