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

Annotations already declare readOnlyHint and idempotentHint, lowering the burden. The description adds non-obvious context: 'No auth required', data provenance ('iRail open data, Belgium national rail'), and the all-vs-filtered listing behavior. This extends the structured 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?

Four sentences, each earning its place: primary action/scope, return fields, downstream usage, and auth/data provenance. The key verb and resource are front-loaded with zero filler.

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 simple list tool with 2 optional params, full schema coverage, output schema present, and safety annotations, the description is complete. It even enumerates the output fields and explains how the result should be chained into liveboard and connections tools.

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% and both parameters are well-documented (lang enum with default, query with filter example and omit-to-return-all behavior). The description reinforces that query filters by name and mentions bilingual names, but doesn't add meaning beyond the schema. 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 ('List'), a precise resource ('700+ SNCB/NMBS Belgian railway stations'), and an optional filter ('or filter by name'). It also enumerates the returned fields (station ID, display name, standard name, lat/long) and implicitly differentiates itself from transit siblings by noting its output feeds liveboard and connections tools.

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?

Explicitly instructs agents to use station names from this list as input for liveboard and connections tools, establishing clear when-to-use workflow context. It does not name exclusions or alternative tools, but the reference-vs-transit distinction is strongly implied.

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