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

Annotations already declare readOnlyHint, idempotentHint, openWorldHint and destructiveHint=false, so the safety and idempotency profile is fully covered. The description adds the useful linguistic note that names may be German, French or Italian, but says nothing about result shape or matching behavior beyond that. With annotations carrying the load, a 3 is appropriate.

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 the purpose, then the usage trigger, then an example — a clean structure with no wasted prose. The inline JSON example is slightly redundant given the schema already shows the required parameter, keeping it from a 5.

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?

There is no output schema, so the description carries some burden of explaining what comes back. It implies a set of matching station names but does not describe the return payload (IDs, coordinates, multiple matches), which matters for a disambiguation/autocomplete-style lookup. Adequate but with a real gap for a no-output-schema tool.

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% on the single 'query' parameter, so the schema already documents it. The description adds only marginal framing ('matching a word', an example value) beyond that. Baseline 3 is correct when the schema does the heavy lifting.

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 ('Finds the exact Swiss station or stop names matching a word'), which is unambiguous. It implicitly separates itself from siblings (which deal with connections and departures) but never names or contrasts them explicitly, so it stops short of a 5.

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 'Use when: a place name is ambiguous or misspelled' line gives a concrete trigger condition, which is more than most definitions. It does not, however, name an alternative tool or state when not to use it, so it lacks the explicit routing a 5 would require.

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