OpenVan MCP Server

Compare Fuel Prices

compare_fuel_prices

Read-onlyIdempotent

Compare current fuel prices across 2-10 countries for one fuel type. Returns a cheapest-first sorted table, so users can see which country has cheaper fuel.

Instructions

Compare current prices for one fuel type across 2-10 countries. Returns sorted table cheapest-first. Use it when someone asks which of two or more named countries has cheaper or more expensive fuel.

Input Schema

TableJSON Schema

Name	Required	Description	Default
`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.
`fuel_type`	No	Fuel type to compare. e.g. gasoline, diesel, lpg, cng, e85.	diesel
`country_codes`	Yes	Array of 2-10 ISO 3166-1 alpha-2 country codes to compare.

Output Schema

TableJSON Schema

Name	Required	Description	Default
No arguments

Schema Changelog

Changes observed during successful MCP inspections.

Changed3 schema fields changedv0.6.4Oct 15, 2026

changedInput schema / properties / fuel_type / description

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

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"
+}

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

A4/5.0

Behavior3/5

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

Annotations already declare readOnlyHint, idempotentHint, openWorldHint and destructiveHint=false, so the safety profile is covered. The description adds the ordering behavior (cheapest-first), which is genuinely useful, but says nothing about rate limits, staleness of 'current' prices, or auth. A 3 reflects modest added value on top of rich annotations.

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

Conciseness5/5

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

Three tight sentences with zero filler, front-loading the operation and scope before the return shape and the usage trigger. Every clause earns its place.

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 an output schema present and annotations covering safety, the description carries only operation, scope, ordering, and a usage trigger, which is sufficient to invoke correctly. Minor gaps: no hint about how 'current' data is sourced or updated, and no contrast with the overlapping fuel siblings.

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%, including the locale guidance and fuel_type default, so the baseline is 3. The description only restates that one fuel type is compared and the 2-10 country range; it adds no meaning beyond what the schema already documents.

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 (compare), resource (current fuel prices), and scope (one fuel type across 2-10 countries), plus the return shape (sorted table cheapest-first). An agent can distinguish this from siblings like get_fuel_prices or find_cheapest_fuel 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.

Usage Guidelines4/5

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

Gives an explicit trigger: 'Use it when someone asks which of two or more named countries has cheaper or more expensive fuel.' That is clear context, but it names no alternatives or exclusions, so an agent still has to guess how it differs from find_cheapest_fuel or rank_food_prices-style siblings.

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