Finish Jupyter Build System Separation

Status: In Progress · Proposal

June 2026¶

Summary of Work Completed¶

• The first stable version, v1.0 was published, along with two patch releases (CHANGELOG.md)

• Rspack version was updated to 2.0 (jupyterlab/jupyter-builder#93)

• Downstream tests were added (jupyterlab/jupyter-builder#91)

• Linters were set up for code quality enforcement (jupyterlab/jupyter-builder#96)

• Core-metadata automatic updates were set up (jupyterlab/jupyter-builder#119)

• The set of dependencies was further reduced and set of network calls restricted (jupyterlab/jupyter-builder#102, jupyterlab/jupyter-builder#108, jupyterlab/jupyter-builder#118)

• Compatibility with old @jupyterlab/builder was improved for smoother transition (jupyterlab/jupyter-builder#98)

• We investigated and patched the breakage to builder packages due to a new webpack release which affected both @jupyterlab/builder and the new jupyter-builder before rspack transition (webpack/webpack#20860, https://github.com/krassowski/webpack-licence-repro, jupyterlab/jupyterlab#18929, jupyterlab/jupyterlab#19021)

We track most of the issues and pull requests associated with this proposal in this public GitHub project.

Deliverables/Milestones¶

Documentation

We added migration documentation:

• in JupyterLab extension migration guide https://jupyterlab.readthedocs.io/en/latest/extension/extension_migration.html#migrating-to-jupyter-builder

• in a dedicated blog post https://blog.jupyter.org/announcing-jupyter-builder-a-standalone-build-system-for-jupyterlab-extensions-c3d4cc06fa95

Metric 3. Feedback sought from maintainers, packagers and extension developers confirms that they are willing to use the new builder package

We received feedback from multiple extension developers and packages and are working to address it:

• jupyterlab/jupyter-builder#127

• jupyterlab/jupyter-builder#120

• jupyterlab/jupyter-builder#116

Challenges or Risks¶

None

Budget Update¶

As of 23rd June we used 6,740.50 USD out of 14,904 USD budget.

Next Steps¶

Address the feedback from extension developers and packagers.

April 2026¶

Summary of Work Completed¶

• The npm package was renamed to jupyter/builder (jupyterlab/jupyter-builder#60)

• The webpack bundler was replaced with rspack as per direction set earlier by JupyterLab (jupyterlab/jupyter-builder#54)

• The core dependency metadata handling was implemented using npm-versioned core metadata package (jupyterlab/jupyter-builder#57)

• The builder was integrated into JupyterLab (jupyterlab/jupyterlab#18723)

• The builder package was published on conda-forge (conda-forge/staged-recipes#32925)

• Documentation was added (jupyterlab/jupyter-builder#69)

• Dependency and packaging issues were ironed out (jupyterlab/jupyter-builder#72, jupyterlab/jupyter-builder#75, jupyterlab/jupyter-builder#74, jupyterlab/jupyter-builder#79)

• We investigated future direction for reducing the complexity for downstream users (e.g. not requiring a Node.js, bundling required dependencies, etc)

We track some of the issues and pull requests associated with this proposal in this public GitHub project.

Deliverables/Milestones¶

Documentation

Initial documentation done

Metric 2. JupyterLab and at least one extension successfully migrates to using jupyter-builder

Done for JupyterLab

Metric 3. Feedback sought from maintainers, packagers and extension developers confirms that they are willing to use the new builder package

Community adapted the builder in:

• Notebook (jupyter/notebook#7893)

• JupyterLite (jupyterlite/jupyterlite#1932)

Challenges or Risks¶

None

Budget Update¶

As of 26th April 2026 we used 3,545.50 USD out of 14,904 USD budget.

Next Steps¶

• Documenting migration in JupyterLab documentation

• Migration to rspack 2.0 from 1.x series

• Add downstream tests

• Improve code quality from pre-existing code

• Publish v1.0 pre-release

February 2026¶

Summary of Work Completed¶

• CI was updated and bundled package manager issues were fixed

• The PyPI package was transferred to Project Jupyter

• A new version of the jupyter-builder was released

• Initial support for full decoupling from JupyterLab dependency was merged

• Future directions were agreed with the community feedback on:

  • naming of the package

  • transition to rspack

  • the way of obtaining the core metadata required for build

We track some of the issues and pull requests associated with this proposal in this public GitHub project.

Deliverables/Milestones¶

• A stable version of jupyter-builder is published: first functional (although not yet stable) version was published

• Integrating into the JupyterLab core and extension template: a draft PR was opened against the extension-template repository

Challenges or Risks¶

Since the proposal was written the bundler in core JupyterLab was swapped from webpack to rspack. This requires additional work to catch up and (potentially) support both bundlers initially.

Budget Update¶

As of 20th Feb 2026 we used 817 USD out of 14,904 USD budget.

Next Steps¶

• Creation of documentation for jupyter-builder and documenting migration in JupyterLab documentation

• Migration to rspack

• Publishing core package metadata for future and past supporter JupyterLab releases