Free tool
YOLO TXT to COCO JSON Converter
Merge YOLO .txt label files or a ZIP archive into one COCO JSON file with absolute pixel coordinates.
Convert annotation format
Pick the output format, then choose one or more files or a ZIP. Add the images too when the labels do not include image sizes, such as YOLO. The result downloads as soon as it is ready.
Downloads a single annotation file.
Quick conversions
Converting YOLO Normalized Labels to COCO JSON
YOLO Format (Per Image .txt)
YOLO stores one txt file per image with normalized values:
0 0.500000 0.500000 0.250000 0.400000 1 0.200000 0.800000 0.100000 0.150000
COCO JSON Format (Unified)
COCO combines all images, categories, and bboxes into one JSON:
{
"images": [{"id": 1, "file_name": "img1.jpg", "width": 1920, "height": 1080}],
"categories": [{"id": 0, "name": "person"}],
"annotations": [{"id": 1, "image_id": 1, "category_id": 0, "bbox": [720, 324, 480, 432]}]
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Frequently asked questions
- What do I need to upload to convert YOLO to COCO?
- Upload your YOLO TXT label files together with the images, or a ZIP that contains both. COCO stores pixel coordinates, so each image is needed to read its size, and labels without a matching image are skipped. Include classes.txt or data.yaml so class indexes become named categories.
- Does the converter produce a single COCO file?
- Yes. All label files are merged into one COCO JSON file with images, categories, and annotations sections, which most training frameworks and labeling tools can import.
- Can I convert YOLO segmentation labels?
- The YOLO to COCO converter is built for bounding box labels. If your dataset has polygons, check the result before training, or convert from a polygon-aware format such as COCO or LabelMe instead.
- Are my files uploaded?
- The files you select are sent to LabelOp servers for processing, and the result comes back as a download. You do not need an account.