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

Annotations already set readOnlyHint=true and openWorldHint=true, lowering the burden. The description adds useful behavioral context: it uses the official SNCF API, covers a wide range of train types, and explicitly states what cannot be looked up (PNRs, agency refs). This goes beyond the annotations without contradicting them.

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?

Three sentences, front-loaded with the core function. The content is dense and informative, with no filler. Slightly verbose due to the detailed train coverage and exclusions, but every sentence earns its place.

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 no output schema, the description adequately notes it returns 'route, stations and scheduled times'. It covers usage scenarios, exclusions, coverage, and what not to do, making it fully self-contained for an agent to decide when and how to invoke the 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 coverage is 100% for both parameters, so baseline is 3. The description adds meaningful semantics by explaining train number formats with examples, emphasizing digits-only with optional prefixes, and clarifying that 6-char codes and long refs are not valid inputs — enriching the schema description.

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 clearly states the verb+resource: 'Resolve a TRAIN NUMBER to its route, stations and scheduled times'. It is specific to train numbers and distinguishes itself from siblings like resolve_flight and resolve_location by covering rail travel and explicitly enumerating train operators.

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 explicit usage context: use when a customer books a station pickup/drop-off or Meet & Greet and gives a train number to verify times. It also gives clear exclusions by identifying PNR and agency booking references as invalid, directing the agent to extract info from the customer's confirmation instead.

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