Pixtral Large

Most "describe this image" nodes in ComfyUI - Florence2, JoyCaption, WD14 Tagger - are local models you download and run on your own GPU. Pixtral Large is the odd one out in that group: it's a node that calls a cloud API. You send your image and a prompt to Mistral AI's servers, their 124B-parameter Pixtral Large model does the looking, and you get text back. No checkpoint to fetch, no VRAM budget to fight for, but you do need an internet connection and a Mistral API key.

That trade-off is exactly why people reach for it. In a r/comfyui thread asking for the best current option for turning an image into a prompt, one reply named "Pixtral Large/Janus" alongside the usual local suspects, and another commenter separately confirmed "Mistral works very good for me." It's a real option people cite for this job, not a novelty - it's just a different kind of option, one that trades local compute for a network call and an account.

What it's actually doing

Pixtral Large is 123B decoder parameters plus a 1B vision encoder, with a 128K context window, and it's genuinely strong at things local captioners often struggle with: dense OCR across scripts, and multi-page or multi-image reasoning in one shot (up to 30 images, via this pack's MultiImagesInput node). The README leans hard on multilingual OCR specifically - Hebrew, Arabic, Chinese, Japanese, Korean and more, responding in the same language you asked in, not just transcribing it. If your job is "extract this document" or "describe this in Hebrew," that's a real edge over English-centric local taggers. Mistral AI is also the outfit behind the vision-language text encoder Flux 2 Dev uses, for reference on how seriously to take their vision work.

The node itself is a thin wrapper: build the request from your inputs, send it, return the text. All the actual intelligence lives on Mistral's side.

Inputs and outputs that matter

• prompt (STRING, default "Describe the image") - your instruction. Can be a plain caption request, an OCR ask, a comparison across a batch, or a question in any of the languages Pixtral handles - the model responds in kind.
• images (IMAGE) - one image from Load Image, or a batch from this pack's MultiImagesInput node if you're sending more than one.
• api_key (STRING) - your Mistral AI key. The default value is a placeholder string telling you to enter your own; nothing runs until you replace it.
• temperature (0–1.5, default 0.7) - response randomness. Push it down toward 0 for OCR and factual extraction where you want the same answer every time; leave it near default or push it up for looser, more descriptive captioning.
• maximum_tokens (1–32768, default 4096) - hard cap on response length. Lower it if you're getting truncated or costly responses; raise it for long document transcriptions.
• top_p (0–1, default 1) - nucleus sampling. Most people leave this alone; temperature is the knob that actually matters for day-to-day use.

Output is a single STRING - wire it into Preview Text to read it, or into anything downstream that takes text, like using the description as a prompt for a generation node.

How to install it

Search "ComfyUI Pixtral Large Extension" in ComfyUI Manager, or clone it manually:

cd ComfyUI/custom_nodes
git clone https://github.com/ShmuelRonen/ComfyUI_pixtral_large.git

Restart ComfyUI. There's no model download step, because the model doesn't run locally. What you do need is a Mistral AI API key: sign up at mistral.ai, generate a key from the API section, and paste it into the node's api_key field. The README calls it a free key to obtain - that gets you access, but treat actual usage the way you'd treat any hosted LLM call: keep maximum_tokens reasonable if you're running this at any real volume, since every call is a request against your account, not a free local inference.

Common issues & troubleshooting

The README's own error handling section covers the three you'll actually hit:

• "API Error" - verify the key is correct and pasted in full, and check your internet connection. This is the catch-all for anything Mistral's API rejected, including an invalid or expired key.
• "Invalid prompt" - check formatting; an empty or malformed prompt string is the usual cause.
• "Token limit exceeded" - lower maximum_tokens. This shows up most on big multi-image or long-document jobs where the response you're asking for is longer than the cap allows.

One thing not in the README but worth knowing: api_key is a plain visible field, not masked. If you post a workflow JSON publicly, clear it first - ComfyUI won't hide it for you.