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

With no annotations provided, the description carries the full burden of behavioral disclosure. It does disclose that the call 'spends credits like any other call' and uses 'Fetch' to imply a read operation. However, it does not address potential errors, response format, rate limits, or whether any route could have side effects, leaving behavioral coverage incomplete for a generic route caller.

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, each earning its place: purpose, prerequisite workflow, parameter explanation with example, and cost note. It is front-loaded with the core function and contains no filler.

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 tool's generic nature and lack of output schema or annotations, the description covers the key operational aspects: what to call, how to discover the path, how to pass parameters, and that credits are consumed. It could mention the response shape or error handling, but for a generic route caller with this complexity, it is reasonably complete.

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 provides zero description coverage, so the description must compensate. It does so by explaining that `params` are query parameters and giving a concrete example with both `path` and `params`. This adds real meaning beyond the bare schema, though it does not fully elaborate on path formats or edge cases.

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: 'Fetch any Fetchwire route by path.' It clearly distinguishes itself from sibling operation tools by targeting 'the routes the operation tools do not cover,' and names list_routes as the discovery mechanism. This is specific enough for an agent to understand exactly what call_route is for.

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 explicit context for when to use this tool: for routes not covered by operation tools, and instructs the agent to find the path with list_routes first. However, it does not name the specific operation tools as alternatives, instead referring to them as a category ('operation tools'), which is clear but slightly less direct than naming the siblings.

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