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

Annotations already declare readOnly/idempotent/openWorld/non-destructive, but the description adds real behavioral context beyond them: hard caps (≤15 rows, ≤120 min, 'over 2 h is refused'), the ambiguity-handling behavior (a bare 'Hauptbahnhof' returns a list and asks, so don't guess), the language-default failure mode, and the requirement to show the attribution line. This is disclosure the structured fields do not carry.

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?

Front-loaded with purpose and tightly packed; almost every clause carries routing or constraint information. It is dense to the point of being cryptic in spots (e.g. 'A line with no DEPARTURE station'), but the length is justified by the number of near-miss siblings and edge cases it must disambiguate.

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 7-parameter tool with no output schema, the description does state the return shape (platform, delay, cancellations, ≤15 rows, attribution line) and all key limits. Minor gaps remain around the not-found/invalid-station failure path and pagination beyond the row cap, but overall it is sufficient to call 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?

Schema coverage is 100% so the baseline is 3, and much of the description's parameter text mirrors the schema (e.g. the language/default guidance). It still adds cross-parameter meaning an agent needs: 'Give either station OR eva_no, never both', 'pair [categories] with a longer duration_min', 'no destination filter', and the train-type mapping for colloquial terms.

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?

Specific verb+resource: 'Next trains from a German railway station: platform, delay, cancellations.' It explicitly distinguishes itself from get_departures ('Do NOT use for buses, trams, a non-railway stop, another day or a time over 2 h away') and check_transit_disruption, so an agent can route without opening a schema.

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?

Gives explicit when-to-use ('when a train, S-Bahn or ICE leaves a named station', lateness questions, 'heute Abend' stays here), explicit when-not (buses/trams/non-railway stops/later days/>2 h), and names the two alternative tools with the condition that selects each. Nothing is left to inference.

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