Getting Started

Everything you need to integrate NPR API into your application.

NPR API provides a simple REST API for number plate recognition. Upload an image containing a vehicle and receive the detected plate registration along with a confidence score. Results can optionally be enriched with DVSA vehicle data and AI scene intelligence.

Quick Start

1. Create an account and navigate to Settings → API Keys
2. Generate a new API key
3. Make your first recognition request using the key

curl -X POST https://nprapi.com/api/v1/recognise \
  -H "X-API-Key: YOUR_API_KEY" \
  -F "image=@plate.jpg"

{
  "success": true,
  "registration": "AB12 CDE",
  "confidence": 95,
  "credits_used": 1,
  "processing_time_ms": 1420
}

Authentication

All API requests require authentication via an API key. Include your key in the X-API-Key header on every request.

X-API-Key: your-api-key-here

Requests without a key, or with a key that has been deactivated, receive a 401 response:

{
  "success": false,
  "error": "Invalid or inactive API key"
}

Managing API Keys

You can create and revoke API keys from your dashboard under Settings → API Keys. Each key can be given a descriptive name to help you identify its purpose.

Making Requests

The API accepts multipart/form-data requests. Images can be sent either as file uploads or as base64-encoded form fields.

Base URL

https://nprapi.com/api/v1

Request Headers

Image Requirements

• Supported formats: JPEG, PNG, WebP, HEIC, AVIF
• For best results, ensure the plate is clearly visible and in focus

Recognition API

The recognition endpoint processes a single image synchronously and returns the detected number plate with a confidence score. Optionally, each result can be enriched with DVSA vehicle data (make, model, colour, fuel type, engine size) and scene intelligence (an AI analysis of the image itself).

POST /api/v1/recognise

Submit an image for number plate recognition. Provide either image or image_base64.

Request Parameters

Response

{
  "success": true,
  "registration": "AB12 CDE",
  "confidence": 95,
  "credits_used": 1,
  "processing_time_ms": 1420
}

When multiple is enabled, the response contains a plates array instead:

{
  "success": true,
  "plates": [
    {
      "registration": "AB12 CDE",
      "confidence": 95,
      "country": "GB"
    },
    {
      "registration": "XY21 ZZZ",
      "confidence": 88,
      "country": "GB"
    }
  ],
  "processing_time_ms": 1650
}

Vehicle Data & Scene Intelligence

Enable vehicle and/or scene to enrich the result. Each adds 1 credit to the request — see Credits & Usage. The flags can be sent as form fields or query string parameters:

curl -X POST https://nprapi.com/api/v1/recognise \
  -H "X-API-Key: YOUR_API_KEY" \
  -F "image=@plate.jpg" \
  -F "vehicle=true" \
  -F "scene=true"

The response then includes the requested data. Vehicle data is null where DVSA holds no record for the registration:

{
  "success": true,
  "registration": "AB12 CDE",
  "confidence": 95,
  "vehicle": {
    "make": "FORD",
    "model": "FOCUS",
    "colour": "BLUE",
    "fuel_type": "PETROL",
    "engine_size": "999cc"
  },
  "scene": {
    "vehicle_type": "car",
    "make": "Ford",
    "model": "Focus",
    "colour": "blue",
    "environment": "street",
    "time_of_day": "day",
    "weather": "clear",
    "vehicles_visible": 1,
    "description": "A blue hatchback parked on a residential street."
  },
  "credits_used": 3,
  "processing_time_ms": 1685
}

In multiple mode the vehicle object appears on each entry in the plates array instead. The scene object always describes the image as a whole, so it appears once at the top level. The scene fields are:

Response Fields

If recognition fails, the API responds with a 422 status and an error message:

{
  "success": false,
  "error": "No plate detected",
  "processing_time_ms": 980
}

Batch Processing

For processing multiple images at once, use the batch endpoint. Batches are processed asynchronously — submit your images, then poll the status endpoint for results.

POST /api/v1/batch

Submit multiple images in a single request. Provide files via images[], base64 strings via images_base64[], or a combination of both. The multiple parameter works the same as on the recognise endpoint. The vehicle and scene parameters are not currently supported on batches.

curl -X POST https://nprapi.com/api/v1/batch \
  -H "X-API-Key: YOUR_API_KEY" \
  -F "images[]=@plate1.jpg" \
  -F "images[]=@plate2.jpg" \
  -F "images[]=@plate3.jpg"

{
  "success": true,
  "batch_uuid": "9c2f1a4e-6b3d-4f8a-9e01-2d7c5b8a4f10",
  "total_requests": 3
}

GET /api/v1/batch/{uuid}

Retrieve the status and results of a batch. Poll this endpoint until status is completed or failed.

curl https://nprapi.com/api/v1/batch/9c2f1a4e-6b3d-4f8a-9e01-2d7c5b8a4f10 \
  -H "X-API-Key: YOUR_API_KEY"

{
  "success": true,
  "batch_uuid": "9c2f1a4e-6b3d-4f8a-9e01-2d7c5b8a4f10",
  "status": "processing",
  "total_requests": 3,
  "completed_requests": 1,
  "progress_percent": 33,
  "requests": [
    {
      "uuid": "5e8b2c1d-9f4a-4b7e-8c30-6a1d9e2f5b48",
      "status": "completed",
      "registration": "AB12 CDE",
      "confidence": 95,
      "processing_time_ms": 1420,
      "success": true,
      "error": null,
      "plates": [
        {
          "registration": "AB12 CDE",
          "confidence": 95,
          "country": "GB"
        }
      ]
    }
  ]
}

Status Values

Credits & Usage

Usage is measured in credits. Every plan includes a monthly credit allowance, and each request consumes credits based on the features used:

Every response includes a credits_used field, and your live usage is returned on every API response via headers:

When your allowance is exhausted the API responds with 429 and a usage summary. Paid plans can enable overage billing from the Plan page — requests then continue past the allowance and additional credits are billed on the 1st of the following month.

{
  "success": false,
  "error": "Monthly credit allowance exceeded...",
  "usage": {
    "included": 500,
    "used": 500,
    "remaining": 0
  }
}

Failed requests (server errors) are never billed. Requests where no plate is detected are billed as normal — the image is still fully processed.

Error Handling

The API uses standard HTTP status codes to indicate success or failure. All error responses include a JSON body with a human-readable message.

{
  "success": false,
  "error": "No image provided"
}

Status Codes