The lockfile

open-assets render keeps a file called assets.lock in the project directory. It records what each output was rendered from, so the next run skips images whose inputs have not changed.

Done. 0 asset(s) rendered, 11 skipped (unchanged) in 0.0s.

What is in itCopy Anchor Link

{
  "version": 1,
  "assets": {
    "screenshots/01-hero": {
      "exports/screenshots/iphone-6.9/01-hero.png": {
        "sourceChecksum": "sha256:03d1...",
        "outputPath": "exports/screenshots/iphone-6.9/01-hero.png",
        "exportedAt": "2026-10-28T18:57:53.222Z",
        "exportChecksum": "sha256:543e..."
      }
    }
  }
}

• The asset key is <collection>/<template>, or <collection>/<locale>/<template> when localized.
• Each output is keyed by its path, relative to the project directory, so the file is portable across machines.
• sourceChecksum hashes the template and its direct local dependencies.
• exportChecksum hashes the export settings: width, height, outFile and locale.

When an image is skippedCopy Anchor Link

An output is skipped only if all of these hold:

1. The lockfile has an entry for that asset and output path.
2. The current source checksum matches sourceChecksum.
3. The current export checksum matches exportChecksum.
4. The recorded outputPath matches.
5. The output file exists on disk.

Anything else re-renders it. So a deleted PNG is regenerated, and changing a size or an outFile re-renders that size.

What the source checksum coversCopy Anchor Link

For an .html template, the checksum includes the file plus every local file it references directly through src="...", href="..." or url(...). A path counts if it resolves, relative to the template's folder, to a file that exists. http(s)://, //, data: and # references are ignored.

That means these changes do trigger a re-render:

• Editing the template.
• Editing a stylesheet it links, such as ../../public/styles.css or ../../dist/styles.css.
• Replacing an image it references, such as ../../public/screenshots/01-home.png.

These do not:

• Files referenced from inside a stylesheet (fonts or images in a CSS url() in an external .css file). Only the template's own text is scanned.
• Root-relative references like /logo.png. They resolve against the filesystem root, not your project.
• Files a script loads or a URL built at runtime, such as the Skimmer example's locale image swap.
• Remote assets (Google Fonts, CDNs).
• localizations.json. Changing a string does not invalidate the cache.
• sourceSize, background and the renderer's version.

For .svg templates only the SVG file itself is hashed.

--forceCopy Anchor Link

npx open-assets render --force

Ignores the cache and renders everything selected (it still updates the lockfile). Use it after changing something the checksum does not see: a translation, a font, a nested CSS asset, a sourceSize, or after upgrading Open Assets.

Other behaviorCopy Anchor Link

• A missing or invalid assets.lock is treated as empty: everything renders and a fresh file is written.
• The lockfile is saved even when a render fails mid-run, so finished images stay cached.
• Output actions (xcode, copy-source) are not cached; they run on every render.
• The dev server does not read or write the lockfile.

Commit itCopy Anchor Link

Commit assets.lock so teammates and CI share the cache. Remember that condition 5 requires the output file to exist: a fresh checkout where exports/ is gitignored will render everything once, then stay incremental. outFile destinations that you commit (like public/favicon.png) are skipped right away.

RelatedCopy Anchor Link

• render reference
• CI with GitHub Actions