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JavaScript
Remote

find_cheapest_fuel

Read-onlyIdempotent

Compare fuel prices and locate low-price filling stations near a place or coordinates. Use when users ask where to fill up or what fuel costs.

Instructions

Returns the cheapest stations for one fuel grade near a place or coordinate: price per litre, brand, address, distance, open state. Use when the user asks where to fill up or what fuel costs. Do NOT use for charging an electric car (call find_charging_station), price history, or traffic (call check_autobahn_traffic). Radius ≤ 25 km, at most 10 stations. For a brand, a name, open now or at a named time, or nearest-first, call find_fuel_station. Each line names the age of its price and opening-hours claim. Prices are consumer information only; the attribution line and MTS-K note must be shown.

Input Schema

TableJSON Schema
NameRequiredDescriptionDefault
latNoLatitude in WGS 84, e.g. 48.137. Use with lon when the caller already holds coordinates; otherwise use place.
lonNoLongitude in WGS 84, e.g. 11.576. Use with lat; otherwise use place.
fuelNoFuel grade: "e5" (Super E5), "e10" (Super E10, the standard German petrol) or "diesel". Default "e10". Pass the grade the person named — a diesel driver is not helped by a petrol price.e10
limitNoHow many stations to return, cheapest first (1–10, default 5). The provider's terms cap it at 10.
placeNoWhere to look, as free text: a city ("München", "Munich"), a district or Kreis ("Kreis Fulda"), a Bundesland, a station or stop ("Hamburg Hbf"), a motorway ("A7"), or a street address with a house number ("Hauptstraße 12, 36037 Fulda"). Use this instead of coordinates whenever the person named a place. An address needs its town or postcode — a street and a number alone exist in many towns. Give either place OR lat+lon, never both.
languageNoSet this on every call to the language the person is writing in: "en" if they wrote English, "de" if they wrote German. Do not leave it out because it has a default — the default is only the fallback when the language is genuinely unclear, and an English question answered in German is a wrong answer. Place names, station names and road numbers are never translated in either language; in English the German term is kept in parentheses so the person recognises it on signs and in local apps.de
radius_kmNoSearch radius around the place in kilometres (1–25, default 5). The provider's terms cap it at 25 km — a larger circle is a dataset request, not a consumer question.

Schema Changelog

Changes observed during successful MCP inspections.

  1. Changed1 schema field changedv1.7.3
    • addedInput schema / properties / place / maxLength
      Added value: +120
  2. First observedv0.0.9

TDQS

A4.3/5.0
Behavior4/5

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

Annotations already cover read-only, idempotent, open-world safety, so the description correctly spends its budget on non-structured constraints: radius ≤ 25 km, max 10 stations, per-line price/opening-hours age, and the MTS-K attribution/display obligation. It stops short of noting rate limits or fallback behavior when no station matches.

Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.

Conciseness4/5

Is the description appropriately sized, front-loaded, and free of redundancy?

Front-loaded with purpose, then usage, then exclusions, then limits. Dense but mostly high-value; the 'Each line names the age...' sentence is useful, though the attribution sentence is a compliance note rather than invocation guidance.

Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.

Completeness4/5

Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?

For a 7-param, no-output-schema, read-only search tool, the description covers selection, exclusions, hard limits, and output-content expectations plus a legal display note. It never mentions result ordering guarantees beyond 'cheapest' or failure modes (no results, invalid place), but those are minor.

Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.

Parameters3/5

Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?

Schema description coverage is 100% and the parameter descriptions are unusually rich (place vs lat/lon mutual exclusion, language default pitfall, fuel enum meaning). The description only echoes the radius and limit caps, adding little beyond the schema. Baseline 3 applies.

Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.

Purpose5/5

Does the description clearly state what the tool does and how it differs from similar tools?

States a specific verb (Returns), resource (cheapest stations), and scope (one fuel grade near a place or coordinate), with an enumerated return payload. It explicitly separates itself from find_fuel_station, find_charging_station, and check_autobahn_traffic.

Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.

Usage Guidelines5/5

Does the description explain when to use this tool, when not to, or what alternatives exist?

Gives the triggering condition ('when the user asks where to fill up or what fuel costs'), explicit exclusions with named alternatives, and a routing rule: brand/name/open-now/nearest-first goes to find_fuel_station. 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.

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