Single .qmd file inside website project no longer previews in RStudio Viewer (regression in 1.9.x)

[ManuelSpinola]

I have:

• searched the issue tracker for similar issues
• installed the latest version of Quarto CLI
• formatted my issue following the Bug Reports guide

Bug description

Description

When rendering a single .qmd file inside a Quarto website project,
the output no longer appears in the RStudio Viewer pane. Instead,
the file is rendered into the _site/ directory as if the entire
website was being built.

This worked correctly in previous versions of Quarto.

Environment

• Quarto CLI: 1.9.37
• R quarto package: 1.5.1
• R version: 4.6.0
• RStudio: 2026.4.0.526

Steps to reproduce

1. Open a Quarto website project in RStudio
2. Open a .qmd file located in a subdirectory (e.g. fundamentos/autocorrelacion_espacial/autocorrelacion_espacial.qmd)
3. Click the Render button in RStudio

Expected behavior

The file renders in isolation and the output is displayed in the
RStudio Viewer pane, as it did in previous versions of Quarto.

Actual behavior

The file is rendered in the context of the full website project and
the output is sent to _site/. Nothing appears in the RStudio Viewer.

Additional notes

Using rmarkdown::render() on the same file also fails to show
output in the Viewer.

Steps to reproduce

No response

Actual behavior

No response

Expected behavior

No response

Your environment

No response

Quarto check output

uarto check
Quarto 1.9.37
[✓] Checking environment information...
Quarto cache location: /Users/manuel_nuevo/Library/Caches/quarto
[✓] Checking versions of quarto binary dependencies...
Pandoc version 3.8.3: OK
Dart Sass version 1.87.0: OK
Deno version 2.4.5: OK
Typst version 0.14.2: OK
[✓] Checking versions of quarto dependencies......OK
[✓] Checking Quarto installation......OK
Version: 1.9.37
Path: /Applications/quarto/bin

[✓] Checking tools....................OK
TinyTeX: v2025.11
Chromium: (not installed)
Chrome Headless Shell: (not installed)
VeraPDF: (not installed)

[✓] Checking LaTeX....................OK
Using: TinyTex
Path: /Users/manuel_nuevo/Library/TinyTeX/bin/universal-darwin
Version: 2025

[✓] Checking Chrome Headless....................OK
Using: Chrome found on system
Path: /Applications/Google Chrome.app/Contents/MacOS/Google Chrome
Source: MacOS known location

[✓] Checking basic markdown render....OK

[✓] Checking R installation...........OK
Version: 4.6.0
Path: /Library/Frameworks/R.framework/Resources
LibPaths:
- /Library/Frameworks/R.framework/Versions/4.6/Resources/library
knitr: 1.51
rmarkdown: 2.31

[✓] Checking Knitr engine render......OK

[✓] Checking Python 3 installation....OK
Version: 3.12.13 (Conda)
Path: /Users/manuel_nuevo/Library/r-miniconda-arm64/envs/r-reticulate/bin/python
Jupyter: (None)

  Jupyter is not available in this Python installation.
  Install with conda install jupyter

[✓] Checking Julia installation...

[mcanouil]

If I understand correctly, it seems to be a bug that is now resolved.
Are you sure the behaviour change is from your update or Quarto CLI and not your update of RStudio?

Running quarto render/preview in a website project on any files will render them as part of the website not as standalone documents.

You are mentioning RStudio, did you try using Quarto CLI from the command line and/or in another IDE?

Finally, you said rendered files are sent in _site/ which is the normal behaviour for website projects, so isn't the bug not only about RStudio panel not displayed the document?