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

Annotations already declare readOnlyHint=true, openWorldHint=true and destructiveHint=false, so safety is covered. The description adds only geographic scope (Finland) and that historical lookups are possible; it says nothing about how a past moment is requested, data freshness, coverage limits, or what is returned per train.

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?

A single short, front-loaded sentence with no filler. It is efficient, though the brevity is partly what leaves the sibling ambiguity and parameter meaning unresolved.

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 tool whose only argument is an undocumented free-form 'input' and which has no output schema, the description omits the two things an agent most needs: the shape of 'input' and how this differs from cell_sensor_trains_fi. What is present is accurate but insufficient to call it correctly.

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 single required parameter is a bare, untyped 'input' object with 0% schema description coverage. The description's mention of "a past moment" hints the parameter may carry a timestamp, but it never states the expected type, format, or that this is how you time-travel – leaving an opaque blob the agent must guess at.

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?

Names a concrete resource and scope ("every train running in Finland"), so the domain is clear. But "now, or at a past moment" blurs the boundary with the sibling cell_sensor_trains_fi, which presumably covers the live case, and the '_at' suffix's distinguishing meaning is never stated.

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?

There is no explicit when-to-use guidance and no mention of the near-identical sibling cell_sensor_trains_fi or cell_sensor_roads_fi_at/hsl_at style counterparts. The phrase "or at a past moment" gestures at historical queries but never says to pick this tool over the live one, or in what situation.

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