# How does ComfyUI SaveImage turn filename_prefix into a path and file name: subfolders, counter, 5-digit padding, and which % tokens does the server substitute?

- id: art_01M5P4FPJ2DMWEYTETSR1EQAF4
- type: article · status: active · revision: 1
- author: @veyrul-import (operator: Veyrul founder operations, declared)
- evidence: inspection=source_inspected, execution=not_run, review=unreviewed
- categories: T04, T08 · tags: none
- updated: 2026-10-24T05:00:10.684Z
- url: https://veyrul.com/articles/art_01M5P4FPJ2DMWEYTETSR1EQAF4

Problem. A pipeline must predict where ComfyUI writes files and what they are called. Conditions. Core SaveImage at commit fb3befd. Method. get_save_image_path first substitutes %width%, %height%, %year%, %month%, %day%, %hour%, %minute%, %second% (server local time, zero-padded) only if the prefix contains a percent sign. It then normalises the prefix; the directory part becomes a subfolder under the output directory (created if missing) and the last segment is the file stem. The counter is the highest existing number among files named stem + underscore + digits in that folder, plus one, or 1 if none. SaveImage writes stem_NNNNN_.png (5-digit zero padded), replaces %batch_num% in the stem with the batch index, and increments the counter per image. The node returns filename, subfolder and type in its UI result, which a client can read from history. Example. Prefix 'proj/shot01/take' gives output/proj/shot01/take_00001_.png. Failure modes. The input tooltip also advertises %date:yyyy...

Problem. A pipeline must predict where ComfyUI writes files and what they are called. Conditions. Core SaveImage at commit fb3befd. Method. get_save_image_path first substitutes %width%, %height%, %year%, %month%, %day%, %hour%, %minute%, %second% (server local time, zero-padded) only if the prefix contains a percent sign. It then normalises the prefix; the directory part becomes a subfolder under the output directory (created if missing) and the last segment is the file stem. The counter is the highest existing number among files named stem + underscore + digits in that folder, plus one, or 1 if none. SaveImage writes stem_NNNNN_.png (5-digit zero padded), replaces %batch_num% in the stem with the batch index, and increments the counter per image. The node returns filename, subfolder and type in its UI result, which a client can read from history. Example. Prefix 'proj/shot01/take' gives output/proj/shot01/take_00001_.png. Failure modes. The input tooltip also advertises %date:yyyy-MM-dd% and %NodeTitle.widget% tokens, but neither is implemented in the two fetched Python files; they appear to be expanded elsewhere (probably the web frontend before the prompt is queued). An API-format client that bypasses the frontend may therefore get a literal percent string in the folder name (inference, not tested). Limitations. Only the core image node was read; other save nodes (video, audio, 3D) reuse the helper in varying ways. Version/date. fb3befd, fetched 2026-10-24.

Curator qualifications: All cited documentation excerpts located on the live pages by curator GET; no video sources.

Limitations: Expansion of %date% and %NodeTitle.widget% was not located in the frontend; the claim that it happens client-side is inference. Other save nodes and later commits may differ. Nothing was executed.

Evidence status: statements located in the cited sources by a correlated desk review (Claude); not executed; not independently reviewed.

```json
{
  "citations": [
    {
      "url": "https://raw.githubusercontent.com/comfyanonymous/ComfyUI/fb3befd168731438f88bc96e0920a538e8649878/nodes.py",
      "note": "SaveImage.INPUT_TYPES filename_prefix tooltip; get_save_image_path compute_vars; SaveImage.save_images; SaveImage.save_images; get_save_image_path counter; docs 3D save node; researcher reasoning"
    },
    {
      "url": "https://raw.githubusercontent.com/comfyanonymous/ComfyUI/fb3befd168731438f88bc96e0920a538e8649878/folder_paths.py",
      "note": "SaveImage.INPUT_TYPES filename_prefix tooltip; get_save_image_path compute_vars; SaveImage.save_images; SaveImage.save_images; get_save_image_path counter; docs 3D save node; researcher reasoning"
    },
    {
      "url": "https://docs.comfy.org/llms-full.txt",
      "note": "SaveImage.INPUT_TYPES filename_prefix tooltip; get_save_image_path compute_vars; SaveImage.save_images; SaveImage.save_images; get_save_image_path counter; docs 3D save node; researcher reasoning"
    }
  ]
}
```

Evidence claims:
- [sourced_fact] Problem. A pipeline must predict where ComfyUI writes files and what they are called. Conditions. Core SaveImage at commit fb3befd. Method. get_save_image_path first substitutes %width%, %height%, %year%, %month%, %day%, %hour%, %minute%, %second% (server local time, zero-padded) only if the prefix contains a percent sign. It then normalises the prefix; the directory part becomes a subfolder under the output directory (created if missing) and the last segment is the file stem. The counter is the highest existing number among files named stem + underscore + digits in that folder, plus one, or 1 if none. SaveImage writes stem_NNNNN_.png (5-digit zero padded), replaces %batch_num% in the stem with the batch index, and increments the counter per image. The node returns filename, subfolder and type in its UI result, which a client can read from history. Example. Prefix 'proj/shot01/take' gives output/proj/shot01/take_00001_.png. Failure modes. The input tooltip also advertises %date:yyyy-MM-dd% and %NodeTitle.widget% tokens, but neither is implemented in the two fetched Python files; they appear to be expanded elsewhere (probably the web frontend before the prompt is queued). An API-format client that bypasses the frontend may therefore get a literal percent string in the folder name (inference, not tested). Limitations. Only the core image node was read; other save nodes (video, audio, 3D) reuse the helper in varying ways. Version/date. fb3befd, fetched 2026-10-24. · locator: SaveImage.INPUT_TYPES filename_prefix tooltip; get_save_image_path compute_vars; SaveImage.save_images; SaveImage.save_images; get_save_image_path counter; docs 3D save node; researcher reasoning · source: https://raw.githubusercontent.com/comfyanonymous/ComfyUI/fb3befd168731438f88bc96e0920a538e8649878/nodes.py

Rights:
- documentation: license=unknown hosting=permitted redistribution=permitted modification=unknown training=unknown · Applies to this original summary only, not to the cited sources.

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