<imgwidth="1024"src="https://github.com/ultralytics/docs/releases/download/0/ultralytics-yolov8-ecosystem-integrations.avif"alt="Ultralytics YOLO ecosystem and integrations">
Validation is a critical step in the [machine learning](https://www.ultralytics.com/glossary/machine-learning-ml) pipeline, allowing you to assess the quality of your trained models. Val mode in Ultralytics YOLOv8 provides a robust suite of tools and metrics for evaluating the performance of your [object detection](https://www.ultralytics.com/glossary/object-detection) models. This guide serves as a complete resource for understanding how to effectively use the Val mode to ensure that your models are both accurate and reliable.
- **[Hyperparameter Tuning](https://www.ultralytics.com/glossary/hyperparameter-tuning):** Use validation metrics to fine-tune your model for better performance.
* YOLOv8 models automatically remember their training settings, so you can validate a model at the same image size and on the original dataset easily with just `yolo val model=yolov8n.pt` or `model('yolov8n.pt').val()`
Validate trained YOLOv8n model [accuracy](https://www.ultralytics.com/glossary/accuracy) on the COCO8 dataset. No arguments are needed as the `model` retains its training `data` and arguments as model attributes. See Arguments section below for a full list of export arguments.
When validating YOLO models, several arguments can be fine-tuned to optimize the evaluation process. These arguments control aspects such as input image size, batch processing, and performance thresholds. Below is a detailed breakdown of each argument to help you customize your validation settings effectively.
Each of these settings plays a vital role in the validation process, allowing for a customizable and efficient evaluation of YOLO models. Adjusting these parameters according to your specific needs and resources can help achieve the best balance between accuracy and performance.
### Example Validation with Arguments
The below examples showcase YOLO model validation with custom arguments in Python and CLI.
### How do I validate my YOLOv8 model with Ultralytics?
To validate your YOLOv8 model, you can use the Val mode provided by Ultralytics. For example, using the Python API, you can load a model and run validation with:
```python
from ultralytics import YOLO
# Load a model
model = YOLO("yolov8n.pt")
# Validate the model
metrics = model.val()
print(metrics.box.map) # map50-95
```
Alternatively, you can use the command-line interface (CLI):
```bash
yolo val model=yolov8n.pt
```
For further customization, you can adjust various arguments like `imgsz`, `batch`, and `conf` in both Python and CLI modes. Check the [Arguments for YOLO Model Validation](#arguments-for-yolo-model-validation) section for the full list of parameters.
### What metrics can I get from YOLOv8 model validation?
YOLOv8 model validation provides several key metrics to assess model performance. These include:
- mAP50 (mean Average Precision at IoU threshold 0.5)
- mAP75 (mean Average Precision at IoU threshold 0.75)
- mAP50-95 (mean Average Precision across multiple IoU thresholds from 0.5 to 0.95)
Using the Python API, you can access these metrics as follows:
```python
metrics = model.val() # assumes `model` has been loaded
print(metrics.box.map) # mAP50-95
print(metrics.box.map50) # mAP50
print(metrics.box.map75) # mAP75
print(metrics.box.maps) # list of mAP50-95 for each category
```
For a complete performance evaluation, it's crucial to review all these metrics. For more details, refer to the [Key Features of Val Mode](#key-features-of-val-mode).
### What are the advantages of using Ultralytics YOLO for validation?
Using Ultralytics YOLO for validation provides several advantages:
- **Convenience:** The models remember their training settings, making validation straightforward.
- **Flexibility:** You can validate against the same or different datasets and image sizes.
- **Hyperparameter Tuning:** Validation metrics help in fine-tuning models for better performance.
These benefits ensure that your models are evaluated thoroughly and can be optimized for superior results. Learn more about these advantages in the [Why Validate with Ultralytics YOLO](#why-validate-with-ultralytics-yolo) section.
### Can I validate my YOLOv8 model using a custom dataset?
Yes, you can validate your YOLOv8 model using a [custom dataset](https://docs.ultralytics.com/datasets/). Specify the `data` argument with the path to your dataset configuration file. This file should include paths to the [validation data](https://www.ultralytics.com/glossary/validation-data), class names, and other relevant details.
yolo val model=yolov8n.pt data=path/to/your/custom_dataset.yaml
```
For more customizable options during validation, see the [Example Validation with Arguments](#example-validation-with-arguments) section.
### How do I save validation results to a JSON file in YOLOv8?
To save the validation results to a JSON file, you can set the `save_json` argument to `True` when running validation. This can be done in both the Python API and CLI.
Example in Python:
```python
from ultralytics import YOLO
# Load a model
model = YOLO("yolov8n.pt")
# Save validation results to JSON
metrics = model.val(save_json=True)
```
Example using CLI:
```bash
yolo val model=yolov8n.pt save_json=True
```
This functionality is particularly useful for further analysis or integration with other tools. Check the [Arguments for YOLO Model Validation](#arguments-for-yolo-model-validation) for more details.
