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

Annotations already declare readOnlyHint=true, idempotentHint=true, and destructiveHint=false, so safety behavior is covered. The description adds useful context by enumerating what the record contains and that it includes links to the crossing page and the FRA source record. It does not state behavior for a missing/invalid ID, but that is a minor omission against otherwise solid coverage.

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?

Two tight sentences: the lookup action and its key identifier come first, followed by the return contents. No filler or redundancy.

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, the description usefully lists the fields returned (road, place, equipment, daily trains, road traffic, and links), and annotations cover the read-only safety profile. Only the not-found/invalid-ID behavior is unaddressed, a minor gap for a simple single-record lookup.

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% and the lone parameter is fully documented in the schema, including the six-digits-plus-letter format. The description restates the same 7-character FRA ID constraint without adding format or validation detail beyond the schema, so 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 (look up), resource (US railroad crossing), and scope (one, by FRA crossing ID). The single-record-by-ID framing clearly separates it from the sibling search/summary tools such as find_crossings_near.

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 description makes the usage condition clear: it applies when you already have a 7-character FRA crossing ID. It does not explicitly name the alternative (e.g. find_crossings_near) for location-based lookups, but the prerequisite is unambiguous.

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