What is a Seed?

The Seed is the exact way the AI calculated your specific image. Each random generation has a unique Seed that is always displayed to the bottom right of your currently selected image.\

Seed number in UI

You can quickly apply the Seed to your seed box by selecting a generation and clicking the Seed number in the bottom right, locking it so that following generations are forced to use the same Seed.
You can also manually type in or paste any Seed in the seed box, but it will only work with numbers.
When the AI Settings box is collapsed, clicking a Seed number that is set there will clear it.

Goose Tip: You can quickly copy the Seed of a previous generation. Simply find the desired generation image and Shift+Click the thumbnail in the history. This will import its Seed directly into the seed box.

Seed numbers can also be found in the filename of downloaded generations and their Exif data.

Plugging in a previously used Seed can assist the AI to generate in the same direction instead of randomly. It's extremely useful for testing how changes in prompts and settings affect images without a luck element.

1girl, blonde hair, twin drills, green eyes, outdoors, garden, smile, red dress 1girl, blonde hair, twin drills, green eyes, outdoors, garden, smile, blue dress

Two images made with the same Seed and settings, except one has red dress in the prompt, and the other has blue dress instead.

Note that there are small differences on the images other than just the dresses' colors. That is normal, since images tagged with red dress and blue dress in the training data are different.

Goose Tip: To generate the exact same image, all settings must match the original generation! This includes the image resolution, number of images generated, as well as any Image2Image reference used.

Be wary that, due to samplers being non-deterministic, the generation will not always turn out 100% the same way as a previous generation!

Also keep in mind that Seeds do not correspond with basic Stable Diffusion generations outside of NovelAI.