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

With no annotations provided, the description carries the full burden of behavioral disclosure. It does not state whether the tool reads data, mutates anything, returns matches, or how it behaves. It is effectively content-free on behavior.

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 text is short, but brevity here is under-specification rather than conciseness. The opening phrase is a confusing headline, and the fragment 'Free text or code' does little to structure or clarify the tool's purpose.

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?

Even for a simple one-parameter search tool, the description omits the core information needed to invoke it correctly: what is being searched, what input is expected, and what result the agent will get. An agent cannot reliably select or use this 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?

The schema only says q is a string with 0% coverage. The phrase 'Free text or code' offers minimal guidance on input format, but it does not explain what q should contain, what kind of search is performed, or how the query is interpreted.

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 never states a verb or resource: 'How to pay — what it is, what you get, what you pay' reads as unrelated payment guidance rather than a search tool. It does not mention searching, rail data, or the q parameter, and it is misleading relative to the tool name rail_search.

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?

No guidance is given for when to use rail_search versus rail_get or any sibling search tool. The lone hint about paying provides no decision criteria, so an agent cannot determine appropriate usage.

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