cars-data.com — Car Specs API

Compare variants

compare_variants

Read-onlyIdempotent

Side-by-side localized specs for 2-4 vehicle variants. This answers from a fixed 40-car demo set. For the full 103,372-variant catalogue call compare_full — paid per call with x402 (USDC on Base), $0.1, no key, no account.

Input Schema

Name	Required	Description	Default
`locale`	No	Response language, one of the 20 published languages (en, ro, fr, de, es, it, sr, hr, pt, pl, cs, sk, hu, no, sv, el, bg, da, ar, tr). Spec labels and enum values come back translated. Default: en.
`variant_ids`	Yes	2 to 4 opaque variant ids from search_cars or filter_cars, e.g. ['v_1a2b3c4d', 'v_5e6f7a8b']

Output Schema

Name	Required	Description
`data`	Yes	One entry per requested variant, in the order asked
`locale`	Yes	Language the response is in
`full_catalogue`	No	Present on demo answers: the paid tool that answers the same question over the full catalogue, with its price

Schema Changelog

Changes observed during successful MCP inspections.

Changed1 schema field changedOct 16, 2026

addedOutput schema / properties / full_catalogue

Added value: +{
+  "description": "Present on demo answers: the paid tool that answers the same question over the full catalogue, with its price",
+  "type": "string"
+}

Changed3 schema fields changedOct 14, 2026

addedInput schema / properties / locale / description

Added value: +"Response language, one of the 20 published languages (en, ro, fr, de, es, it, sr, hr, pt, pl, cs, sk, hu, no, sv, el, bg, da, ar, tr). Spec labels and enum values come back translated. Default: en."

changedInput schema / properties / variant_ids / description

Previous value: -"opaque variant ids from search_cars"New value: +"2 to 4 opaque variant ids from search_cars or filter_cars, e.g. ['v_1a2b3c4d', 'v_5e6f7a8b']"

changedOutput schema / (root)

Previous value: -nullNew value: +{
+  "$schema": "http://json-schema.org/draft-07/schema#",
+  "additionalProperties": {},
+  "properties": {
+    "data": {
+      "description": "One entry per requested variant, in the order asked",
+      "items": {
+        "additionalProperties": {},
+        "properties": {
+          "specs": {
+            "additionalProperties": {
+              "additionalProperties": {},
+              "properties": {
+                "confidence": {
+                  "anyOf": [
+                    {
+                      "type": "number"
+                    },
+                    {
+                      "type": "null"
+                    }
+                  ],
+                  "description": "Confidence score 0–1 for this value; null when not scored"
+                },
+                "label": {
+                  "description": "Spec name in the requested language",
+                  "type": "string"
+                },
+                "unit": {
+                  "anyOf": [
+                    {
+                      "type": "string"
+                    },
+                    {
+                      "type": "null"
+                    }
+                  ],
+                  "description": "Unit of the value (km, kW, l/100km, …); null when unitless"
+                },
+                "value": {
+                  "description": "The value: a string, number or boolean, already localized. Absent when the source holds no value"
+                }
+              },
+              "required": [
+                "label",
+                "unit",
+                "confidence"
+              ],
+              "type": "object"
+            },
+            "description": "Every spec the variant carries, keyed by spec key (e.g. range_wltp_km)",
+            "propertyNames": {
+              "type": "string"
+            },
+            "type": "object"
+          },
+          "variant_id": {
+            "description": "Opaque variant id, e.g. v_1a2b3c4d. Pass it to get_specs / get_images / compare_variants.",
+            "type": "string"
+          }
+        },
+        "required": [
+          "variant_id",
+          "specs"
+        ],
+        "type": "object"
+      },
+      "type": "array"
+    },
+    "locale": {
+      "description": "Language the response is in",
+      "enum": [
+        "en",
+        "ro",
+        "fr",
+        "de",
+        "es",
+        "it",
+        "sr",
+        "hr",
+        "pt",
+        "pl",
+        "cs",
+        "sk",
+        "hu",
+        "no",
+        "sv",
+        "el",
+        "bg",
+        "da",
+        "ar",
+        "tr"
+      ],
+      "type": "string"
+    }
+  },
+  "required": [
+    "locale",
+    "data"
+  ],
+  "type": "object"
+}

Changed5 schema fields changedOct 6, 2026

changedInput schema / properties / locale / enum

Previous value: -[
-  "en",
-  "ro",
-  "fr",
-  "de",
-  "es",
-  "it",
-  "sr",
-  "hr",
-  "pt",
-  "pl",
-  "cs",
-  "sk",
-  "hu",
-  "no",
-  "sv",
-  "el",
-  "bg",
-  "da",
-  "ar"
-]New value: +[
+  "en",
+  "ro",
+  "fr",
+  "de",
+  "es",
+  "it",
+  "sr",
+  "hr",
+  "pt",
+  "pl",
+  "cs",
+  "sk",
+  "hu",
+  "no",
+  "sv",
+  "el",
+  "bg",
+  "da",
+  "ar",
+  "tr"
+]

addedInput schema / properties / variant_ids / description
```
Added value: +"opaque variant ids from search_cars"
```
removedInput schema / properties / variant_ids / items / maximum
```
Removed value: -9007199254740991
```
removedInput schema / properties / variant_ids / items / minimum
```
Removed value: --9007199254740991
```
changedInput schema / properties / variant_ids / items / type
```
Previous value: -"integer"New value: +"string"
```

First observedJul 26, 2026

TDQS

A4.7/5.0

Behavior4/5

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

Annotations already declare readOnly, idempotent and closed-world, so the safety profile is covered. The description adds genuinely non-structured context: the tool is scoped to a 40-car demo set, and the alternative is a paid x402/USDC call with no key. It does not, however, note result size or ordering, which output schema presumably covers.

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?

Two sentences, front-loaded with what the tool does and its data scope, then the routing/pricing contrast. No filler.

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

Completeness5/5

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

With an output schema covering returns, annotations covering safety, and a full-coverage input schema, the remaining burden is scope and alternative routing — both delivered explicitly.

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

Parameters4/5

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

Schema coverage is 100%, so the baseline is 3, but the description adds the demo-set scoping constraint that materially narrows which variant_ids are accepted — information absent from the schema's 'opaque variant ids' wording.

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+resource ('side-by-side localized specs for 2-4 vehicle variants') and immediately bounds the data source ('fixed 40-car demo set'), which cleanly separates it from compare_full.

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?

Explicitly names the alternative (compare_full) and the exact condition that selects it (full 103,372-variant catalogue), plus the cost/key model of that alternative. An agent can route between the two without opening either schema.

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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