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

Annotations already declare this as safe, read-only, idempotent, and open-world, so the description is not carrying the full safety burden. It still adds valuable behavioral context: every candidate is returned with a match quality, no silent choice is made, due_now is included when the expected time passes without a recorded departure, and predictions are unofficial versus official station screens.

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 front-loaded with the core action and then adds only high-value clauses: due_now inclusion, candidate/match-quality return contract, exact-match destination rule, read-only status, and the unofficial-prediction caveat. 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?

For a 6-parameter search tool with no output schema, the description covers result semantics (all candidates with match quality), data reliability, and special temporal handling well. The main remaining gap is that the return shape/fields are not described beyond 'match quality,' which could matter without an output schema.

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 high (83%), so the schema already documents most parameters. The description adds useful nuance for destination matching (station code or full name is an exact match) and for the due_now temporal condition, but it does not clarify headcode, after/before semantics, or include_departed beyond what the schema says.

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 gives a specific verb+resource ('Search for a train') and adds scope details: due_now handling, candidate returns with match quality, and exact-match destination behavior. It implicitly distinguishes itself from a single-result tool like get_train by promising every candidate rather than a silent choice, but it never names any sibling directly.

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?

Usage is only implied. The description explains what the tool does when searching for a train and why candidates/matches are returned, but it does not state when to prefer it over get_train, get_departures, or list_stations, nor does it give exclusions.

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