Export Download Debugging Agent Skill
| Diagnose and fix browser, preview, or Electron export/download failures, especially image export issues involving Save As, Blob/Data URLs, the File System Access API, createWritable failures, and 0 KB files.
Install
one command, takes just this skill from the repositorynpx skills add https://github.com/nexu-io/open-design --skill export-download-debuggingThe instruction itself
5 sections, as written by the authorExport Download Debugging
Use this when an export or download appears to run but produces an empty,
missing, or unusable file. It is tuned for browser previews, iframe capture,
and Electron shells.
Core rule
Separate capture from save. Prove the export payload has non-zero bytes before
debugging the destination path. A 0 KB file often means the native picker or
host created the target file, then the write failed or was blocked.
Evidence
- Record the payload type, MIME type, byte length, object URL or data URL path,
and thrown error name/message.
- Check browser console output and app logs around
showSaveFilePicker,
createWritable, <a download>, URL.createObjectURL, and URL revocation.
- In Electron, inspect the
will-downloadpath: filename, MIME, file extension,
save dialog filters, cancellation, and final file size.
- Confirm the actual downloaded file size on disk and whether it opens in a
normal image viewer.
Fix order
- Prepare and validate the export payload first; disable Save until bytes are
available.
- Prefer the simplest stable save channel for the host. If
showSaveFilePicker().createWritable() fails, is sandboxed, or creates empty
files, route to <a download> or Electron's download manager instead.
- Avoid opening a native picker before the payload is ready. This prevents the
host from creating an empty destination file on later write failure.
- For PNG fallback, prefer a verified non-empty data URL when blob URLs,
revocation timing, CSP, or iframe sandboxing are suspicious.
- In Electron, add explicit Save As filters for exported image extensions
(.png, .jpg, .jpeg, .webp) so users can choose a real image target.
- Keep the UI restrained: format selection, filename/path hint, clear pending
and error states, and one primary save action.
Validation
- Add or update tests for non-empty payload preparation, fallback save behavior,
file extension/MIME mapping, and UI disabled/error states.
- Run focused export tests, then
pnpm --filter @open-design/web typecheck. - If Electron download handling changed, also run
pnpm --filter @open-design/desktop typecheck.
- Before landing, run
pnpm guard, inspect the staged diff for unrelated files,
generated artifacts, and accidental secrets, then use the repository's PR
quality-gate workflow if the fix is being prepared for review.
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How to use it
Take nexu-io/export-download-debugging from the repository into ~/.claude/skills for personal
use, or into .claude/skills inside a project.
The agent identifies a skill by the name field in its header. Two skills with the
same name cannot sit side by side — one of them will be ignored.