Desktop app File viewer: clicking an .html file shows source only — it used to open a rendered preview
Summary
Clicking a generated .html file in the Claude Code desktop app opens the File viewer showing syntax-highlighted source only. There is no rendered-preview option. This is a regression: HTML files used to open as a rendered preview when clicked; at some point (noticed by 2026-08-13) they started opening as source instead.
Workflow affected
Claude generates self-contained HTML deliverables (QA walkthroughs / reports with inline CSS and base64-embedded screenshots) and sends them as file cards in the conversation. Files delivered with display: "render" do render in the side panel once — but any subsequent click on the file card (or the file in the tree) lands in the source viewer. Every re-visit requires asking Claude to run open -a "Google Chrome" <path>, which defeats the point of the in-app viewer.
Expected
Clicking an .html file renders it (as the preview pane does for a URL), ideally with a Source/Preview toggle. This is how it previously behaved.
Actual
Line-numbered, syntax-highlighted source, with no way to switch to a rendered view.
Environment
- Claude Code desktop app, macOS (Darwin 25.5.0)
- Observed 2026-08-13; the previous (rendered) behavior was working within recent weeks
- Repro file: a ~2.5 MB self-contained
walkthrough.html(inline CSS, base64 PNG data URIs) inside a git worktree
Screenshot to follow in a comment (shows the file card on the left and the source-only File viewer on the right).
3 Comments
<img width="1960" height="1417" alt="Image" src="https://github.com/user-attachments/assets/4e431240-bce5-480b-81fb-ccf102c470be" />
Update with a likely mechanism: this is not intermittent, it appears to be a file-size threshold.
Two HTML files generated the same way, clicked the same way, same session:
workload-notes.html, 17 KB (inline CSS, no images) → opens as a rendered preview ✅walkthrough.html, 2.4 MB (inline CSS + base64 PNG data URIs) → opens as source code only ❌So small HTML files still render on click; large ones (somewhere between 17 KB and 2.4 MB) fall back to the source viewer. The regression framing in the original report may just be that my typical generated reports crossed the threshold. A rendered preview (or a Source/Preview toggle) for large self-contained HTML would resolve this — the big files are exactly the ones worth previewing, since they carry embedded screenshots.
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