Error messages

Error while deserializing header: HeaderTooLarge

Error while deserializing header: HeaderTooLarge

A loader node (Load Checkpoint, Load LoRA, DualCLIPLoader, an IPAdapter loader) fails the moment the workflow reaches it:

Error occurred when executing LoraLoader:

Error while deserializing header: HeaderTooLarge

That's from issue #2204. The text comes from the safetensors library, which ComfyUI uses to read model files, and its wording has changed: since safetensors 0.6.0 (June 2025) the same failure prints Error while deserializing header: header too large. Both mean the same thing.

What the header is

A safetensors file starts with eight bytes holding a number, the length of a short JSON index (the header) that lists every tensor in the file. The format's README spells this out. The library refuses a header over 100 MB, a limit its README gives as protection against parsing huge JSON. Real headers are far smaller than that.

So when the first eight bytes of your file decode to something over 100 MB, the library stops with this error. It isn't really saying the header is big. It's saying the start of the file doesn't look like a safetensors file.

How a file ends up like that

The ComfyUI team's replies all point the same way. On #2204 comfyanonymous, who created ComfyUI, wrote, "Your lora file is corrupt or not a safetensors file." A team member on #5838: "Typically, this happens when the model you downloaded is corrupted."

In practice that covers a download that broke partway, a link that saved an error page instead of the model, or a file in another format (.ckpt, .pt) that was renamed. ComfyUI 0.37.0 has its own note for this case, added to the error when it recognizes it: "Make sure this is actually a safetensors file and not a ckpt or pt or other filetype." That note looks for the old HeaderTooLarge spelling, though, so with a current safetensors you may get the bare "header too large" line without it.

How to fix it

Check the file size first. It's quick, and a checkpoint of a few kilobytes can't be a model. If the size is short of what the download page lists, the download broke.

Then download it again. One person in #2643 got past it by reinstalling ComfyUI and downloading the models again, this time with a download manager, having stopped trusting the browser with multi-gigabyte files.

If you have a file that's genuinely in another format, don't rename it. Put it where the loader accepts that format, or use a safetensors copy from the model's page.

When the error names a file you're sure is fine (people in #5826 insisted theirs were), look for a file path in the full message (ComfyUI's added note includes one) and check that exact file, since that's the one the node opened.