Best-price router markets

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

Annotations already declare readOnlyHint, idempotentHint, destructiveHint=false and a closed-world scope, so safety is covered elsewhere. The description's real additions are the disclosure that the data is live/observed rather than cached and that the call is "Free" — useful cost context — but it says nothing about freshness windows, snapshot staleness, or response shape beyond the field list.

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?

One sentence front-loads the resource, then a comma list of returned fields, closed by the cost signal "Free." There is no filler, no restatement of the title, and the most decision-relevant information (what you get, at no cost) arrives first.

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 no output schema and no parameters, the description carries the burden of describing the return payload, and it does so by naming all four categories of data. A short note on response format or refresh cadence would close the remaining gap, but an agent can call this correctly with what is present.

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 and the baseline of 4 applies. The enumeration of returned fields does not need to double as parameter documentation here.

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 resource and surface: the live state of /router best-price markets, then enumerates the exact facts returned (enabled markets, external routing fee, per-market latency, external-execution permission for the key). That is far more specific than a tautology, but it never names a sibling such as carpe_routing_summary or carpe_status, so an agent must infer the boundary itself.

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?

"Live state" plus "whether external execution is open to this key" implies the use case: checking current market availability and permission before routing. There is no explicit when-not guidance and no named alternative (e.g., routing summary vs. per-market latency), so selection against siblings remains implied rather than stated.

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