OpenVan MCP Server

Find Cheapest Fuel

find_cheapest_fuel

Read-onlyIdempotent

Rank countries by fuel price to find the cheapest fuel or most expensive for route planning. Use it to compare diesel, gasoline, LPG, and other fuel types by region or worldwide.

Instructions

Rank countries by the price of a fuel type in a region (or worldwide): the cheapest first, or with order=most_expensive the most expensive first. Useful for route planning. Use it for «where is fuel cheapest» and, with order=most_expensive, «where is fuel the most expensive», in a region or worldwide.

Input Schema

Name	Required	Description	Default
`limit`	No	How many countries to return.
`order`	No	cheapest first (default) or most_expensive first — «where is fuel the most expensive».	cheapest
`locale`	No	Language the user writes in (en, ru, de, fr, es, pt, tr). Set it on every call: the answer and the interactive card are shown in this language and units; without it the card falls back to the app's interface language.
`region`	No	Region to search. Default: world (all countries).	world
`fuel_type`	No	Fuel type. e.g. gasoline, diesel, lpg, cng, e85.	diesel

Output Schema

Name	Required	Description	Default
No arguments

Schema Changelog

Changes observed during successful MCP inspections.

Changed2 schema fields changedv0.9.7Oct 25, 2026
- removedInput schema / additionalProperties
```
Removed value: -false
```
- changedOutput schema / additionalProperties
```
Previous value: -trueNew value: +{}
```

Changed5 schema fields changedv0.6.4Oct 15, 2026

changedInput schema / properties / fuel_type / description

Previous value: -"Fuel type. Uses the same keys as /api/fuel/prices prices."New value: +"Fuel type. e.g. gasoline, diesel, lpg, cng, e85."

changedInput schema / properties / limit / description

Previous value: -"How many cheapest countries to return."New value: +"How many countries to return."

addedInput schema / properties / locale

Added value: +{
+  "description": "Language the user writes in (en, ru, de, fr, es, pt, tr). Set it on every call: the answer and the interactive card are shown in this language and units; without it the card falls back to the app's interface language.",
+  "enum": [
+    "en",
+    "ru",
+    "de",
+    "fr",
+    "es",
+    "pt",
+    "tr"
+  ],
+  "type": "string"
+}

addedInput schema / properties / order

Added value: +{
+  "default": "cheapest",
+  "description": "cheapest first (default) or most_expensive first — «where is fuel the most expensive».",
+  "enum": [
+    "cheapest",
+    "most_expensive"
+  ],
+  "type": "string"
+}

changedOutput schema / (root)

Previous value: -nullNew value: +{
+  "$schema": "http://json-schema.org/draft-07/schema#",
+  "additionalProperties": true,
+  "properties": {},
+  "type": "object"
+}

First observedv0.6.0Oct 3, 2026

TDQS

A3.6/5.0

Behavior3/5

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

Annotations already declare readOnlyHint, idempotentHint, and openWorldHint, so the safety profile is covered. The description adds ranking-order behavior and route-planning relevance, but does not discuss data freshness, coverage limits, or response format.

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?

The description is front-loaded with the ranking behavior and remains fairly short. The final sentence repeats the cheapest/most-expensive examples and region/worldwide scope already implied earlier, adding some redundancy.

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?

With full schema coverage, an output schema, and safety annotations, the description provides enough context to call the tool correctly. It does not need to explain return values, though mentioning locale usage could have made it fully self-contained.

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 coverage is 100%, so all five parameters are already documented in the input schema. The description reinforces the order and region behavior but adds little beyond the schema for limit, locale, or fuel_type.

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

Purpose4/5

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

The description clearly states the specific action: ranking countries by fuel price within a region or worldwide, with optional ordering. It does not explicitly distinguish itself from siblings like compare_fuel_prices or get_fuel_prices, so it stops short of a 5.

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

Usage Guidelines4/5

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

It gives concrete usage contexts such as «where is fuel cheapest» and «where is fuel the most expensive», including the order parameter needed for the latter. It does not state when not to use it or name alternative tools, so it lacks full routing guidance.

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