Convert annotation formats

How To Convert Supervisely JSON to YOLO Darknet TXT

In this guide, we show you how to convert data between the Supervise.ly and YOLO Darknet formats for free. You can use your converted data to train YOLOv3 PyTorch models and other models that support the YOLO Darknet format.

Convert with an AI agent

Paste this prompt into your coding agent

Claude Code, Cursor, Codex or any agent with the Roboflow MCP uploads your Supervisely JSON dataset to Roboflow, generates a version and downloads it as YOLO Darknet TXT.

No Roboflow MCP yet? The prompt has your agent set it up first, or connect your agent before you paste it.

Rather convert it by hand? Follow the steps below

Supervisely JSON

Supervise.ly offers a computer vision platform and uses a proprietary JSON-based annotation format.

Below, learn the structure of Supervisely JSON.

img0001.jsonJSON
{
    "description": "",
    "tags": [
        {
            "id": 12345,
            "name": "train",
            "value": null,
            "labelerLogin": "roboflow",
            "createdAt": "2000-01-01T00:00:00.000Z",
            "updatedAt": "2000-01-01T00:00:00.000Z"
        }
    ],
    "size": {
        "height": 191,
        "width": 264
    },
    "objects": [
        {
            "id": 12345,
            "classId": 67890,
            "description": "",
            "geometryType": "polygon",
            "labelerLogin": "roboflow",
            "createdAt": "2000-01-01T00:00:00.000Z",
            "updatedAt": "2000-01-01T00:00:00.000Z",
            "tags": [],
            "classTitle": "helmet",
            "points": {
                "exterior": [
                    [
                        184,
                        30
                    ],
                    [
                        259,
                        30
                    ],
                    [
                        260,
                        134
                    ],
                    [
                        185,
                        131
                    ]
                ],
                "interior": []
            }
        },
        {
            "id": 12346,
            "classId": 67891,
            "description": "",
            "geometryType": "rectangle",
            "labelerLogin": "roboflow",
            "createdAt": "2000-01-01T00:00:00.000Z",
            "updatedAt": "2000-01-01T00:00:00.000Z",
            "tags": [],
            "classTitle": "person",
            "points": {
                "exterior": [
                    [
                        63,
                        49
                    ],
                    [
                        124,
                        62
                    ]
                ],
                "interior": []
            }
        }
    ]
}

YOLO Darknet TXT

The favored annotation format of the Darknet family of models.

Below, learn the structure of YOLO Darknet TXT.

Each image has one txt file with a single line for each bounding box. The format of each row is:

class_id center_x center_y width height
img0001.txt
1 0.408 0.30266666666666664 0.104 0.15733333333333333
1 0.245 0.424 0.046 0.08
darknet.labels
head
helmet
person

Step 1: Create a free Roboflow account

Roboflow is a universal conversion tool for computer vision annotation formats. To convert your dataset, start by creating a free Roboflow account.

Create free Roboflow account

Step 2: Upload your data into Roboflow

Once your account has been created, click Create New Project. (opens in a new tab)

Roboflow's create project form, with Object Detection selected as the project type

Upload your data to Roboflow by dragging and dropping your Supervisely JSON images and annotations into the upload space.

Roboflow's upload page, with a drag-and-drop area for images, annotations, videos and PDFs

Step 3: Generate Dataset Version

Next, click "Generate New Version" to generate a new version of your dataset:

Roboflow's Generate a Dataset Version page, showing the source images and train/test split for a new version

You can then apply any preprocessing or augmentation steps to your dataset:

The augmentation step of a new dataset version, with 90° Rotate and Brightness added

Step 4: Export Dataset Version

After generating, you will be prompted to Export your dataset. You can choose to receive your dataset as a .zip file or a curl download link. Choose YOLO Darknet TXT when asked in what format you want to export your data. You will see a dropdown with various options like this:

Roboflow's Download dialog, with the export format list open and COCO highlighted

Congratulations, you have successfully converted your dataset from Supervisely JSON format to YOLO Darknet TXT format!

Video Tutorial

Convert Computer Vision Annotation Formats Tutorial

Want to dive deeper into converting annotation formats with Roboflow? In the tutorial below, we explore how to convert your data in the Roboflow dashboard. We also discuss rejecting annotations and train-test-validation splits.

Frequently Asked Questions

Yes! It is free to convert Supervisely JSON data into the YOLO Darknet TXT format on the Roboflow platform.

If you have between a few and a few thousand images, converting data between these formats will be quick. But, the time it takes to convert between data formats increases with the more images you have.

Show guide

Convert Supervisely JSON to other formats

Convert other formats to YOLO Darknet TXT

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