Meld Prompt Constructor

If you've ever run a batch of images and wanted "a random hairstyle from this list" or "one of these three outfits, weighted," you've wanted a wildcard loader. Meld Prompt Constructor is that - it scans a folder of text files, pulls a random (or sequential) line from each, expands dynamic syntax like {A|B|C}, and - the nice bit - automatically moves anything starting with - into a separate negative prompt output.

It's one of ComfyUI-Meld's text utilities, no Image Manager required. Wire its outputs into a CLIP Text Encode and you're off.

How it works

Point directory at a folder (it searches recursively), set file_pattern (default *.txt, so character_*.txt works), and the node reads the files, ignoring any starting with _. From each file it picks one valid line - comments excluded - according to selection_method (random, or sequential based on seed). Then the real work starts:

• Dynamic syntax: {A|B|C} picks one option; {0.1::rare|0.9::common} picks with weights (unweighted items count as 1.0).
• Comments: //, #, and /* */ are stripped, so you can keep notes in your prompt files.
• Auto negative split: any element starting with - is moved to the negative prompt - -low quality becomes a negative, and -(worst quality, bad anatomy) moves the whole group over.
• BREAK: with use_break on (default), prompts from different files are joined with BREAK so CLIP treats them as separate blocks instead of one soup.

The inputs that matter

• directory - where your .txt prompt files live.
• seed - controls both the random line picks and the {A|B} choices, so you can reproduce or vary.
• selection_method - random for variety, sequential for a deterministic tour through your prompts.
• use_break - on by default.

Outputs are just two: positive_prompt and negative_prompt, both plain strings.

Where people get burned

The BREAK keyword is the one real trap. BREAK is meaningful against the old 77-token chunking of SD 1.5 and SDXL - it forces a hard break between prompt blocks. On modern guidance-distilled, LLM-encoded models like Flux, there's no 77-token boundary left, and BREAK is silently meaningless. So if you run this into a Flux workflow, flip use_break to false and let files join with commas, or the keyword just rides along doing nothing.

Also remember the auto-negative split depends on the - prefix, so design your prompt files with that convention in mind - that's the feature that makes this loader nicer than a plain wildcard picker.

Installing it

Same pack, same install as the rest of Meld:

• ComfyUI Manager → search "Meld" → install, or
• comfy node install HappyOnigiri/ComfyUI-Meld, or
• cd ComfyUI/custom_nodes && git clone https://github.com/HappyOnigiri/ComfyUI-Meld.git && cd ComfyUI-Meld && pip install -r requirements.txt then restart.

No models to download. Set up a my_prompts folder, drop a few files in, and you've got a poor man's dynamic prompt engine with clean positive/negative separation built in.