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

Annotations already set readOnlyHint=true and openWorldHint=true, so the description adds value beyond that: it discloses the temporal nature ('right now'), the validity period, the scope of the fee figure, and what is intentionally excluded (no table, no runner-up, no components, no provenance). This contextualizes the tool's minimal behavior well without contradicting 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 three sentences with zero filler. It front-loads the core purpose and outputs, then explains the costs and tradeoff, then points to the alternative. Every sentence earns its place and the contrast with compare_settlement_costs is efficient.

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 simple one-parameter, read-only tool with no output schema, the description covers the returned data (fee, scope, validity), the temporal nature, and the minimal scope. An agent can reasonably expect the return to be a simple record containing those fields; a fully explicit JSON shape is absent, but given the tool's intentional minimalism and annotations, this is sufficient.

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 schema documentation already describes the 'chains' parameter with a full list and default behavior (100% coverage), and the description adds no additional meaning about how to format or choose the comma-separated chains. Baseline of 3 is appropriate since the schema carries the parameter semantics.

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 states a specific verb and resource: 'Returns only the cheapest chain for a USDC transfer' and enumerates the exact outputs (fee in USD, scope, validity). It also differentiates from the sibling paid tool compare_settlement_costs by describing what it deliberately omits, so an agent can tell it apart immediately.

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?

It gives clear context: this is a free, minimal tool for a single cheapest chain 'right now', while explicitly naming the alternative paid tool compare_settlement_costs that offers full comparison. It does not formally state 'do not use when X', but the tradeoff is evident from the wording, satisfying the 'clear context, no exclusions' level.

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