工具路由

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

With no annotations, the description carries the burden and does disclose the outcome shape (choice = index, tool = selected name) and the failure mode (clear error when the service is unavailable), plus the non-destructive selection semantics implied by 'pick one'. It omits any statement about how selection is performed (model-based routing, latency/cost) and says nothing about the `server` override's effect on behavior.

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?

Front-loaded with 何时使用 before 何时不使用, then return values in a single short clause. No filler sentences; each clause carries a distinct decision rule or output fact.

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?

An output schema exists, so the description needn't restate return structure, and it still adds the error case. For a 3-parameter router, the only real remaining gap is how the selection is made and how the optional `server` override changes routing scope; siblings `gate` and `classify` are also not differentiated.

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 coverage is 100%, so the schema already documents `state`, `tools`, and `server` with lengths and counts. The description adds no further meaning about these parameters (e.g., what counts as a good `state` string, whether `tools` must be exact registered names), so the baseline 3 applies.

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 verb and resource: pick the single best-suited tool/handler from a fixed candidate list to serve a request. It explicitly contrasts itself with the sibling `score` (per-candidate quality scoring vs. selection), so an agent can tell the two apart without opening either schema.

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?

Provides an explicit 何时使用 / 何时不使用 pair: use when the candidate list is fixed and one must be chosen; do not use when the list is unstable or the user already named a tool (respect the user, don't re-route), and use `score` instead when you need per-candidate quality. Alternative and exclusion conditions are both spelled out.

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