doc/contributing/large-pull-requests.md

# Large pull requests

* [Overview](#overview)
* [What qualifies as a large pull request](#what-qualifies-as-a-large-pull-request)
* [Who can open a large pull request](#who-can-open-a-large-pull-request)
* [Requirements](#requirements)
  * [Detailed pull request description](#detailed-pull-request-description)
  * [Review guide](#review-guide)
  * [Approval requirements](#approval-requirements)
  * [Dependency changes](#dependency-changes)
* [Splitting large pull requests](#splitting-large-pull-requests)
  * [Feature forks and branches](#feature-forks-and-branches)
* [Guidance for reviewers](#guidance-for-reviewers)

## Overview

Large pull requests are difficult to review or sometimes impossible to review
in the GitHub UI. They are likely to sit for a long time without receiving
adequate review, and when they do get reviewed, the quality of that review is
often lower due to reviewer fatigue. Contributors should avoid creating large
pull requests except in those cases where it is effectively unavoidable, such
as when adding new dependencies.

This document outlines the policy for authoring and reviewing large pull
requests in the Node.js project.

## What qualifies as a large pull request

A pull request is considered large when it exceeds **5000 lines** of net
change (lines added minus lines deleted). This threshold applies across all
files in the pull request, including changes in `deps/`, `test/`, `doc/`,
`lib/`, `src/`, and `tools/`.

Any pull request that adds a new subsystem, e.g. `node:foo` or `node:foo/bar`,
is automatically considered a large pull request and subject to the same rules.

Changes in `deps/` are included in this count. Dependency changes are
sensitive because they often receive less scrutiny than first-party code.

The following categories of pull requests are **excluded** from this policy,
even if they exceed the line threshold:

* Routine dependency updates (e.g., V8, ICU, undici, uvwasi) generated by
  automation or performed by collaborators following the standard dependency
  update process.
* Web Platform Tests (WPT) imports and updates.
* Other bot-issued or automated pull requests (e.g., license updates, test
  fixture regeneration).
* Test-only refactoring that involves no functional changes.
  These pull requests already have established review processes and do not
  benefit from the additional requirements described here.

## Who can open a large pull request

Large pull requests may only be opened by existing
[collaborators](https://github.com/nodejs/node/#current-project-team-members).
Non-collaborators are strongly discouraged from opening pull requests of this size.
Large pull requests from non-collaborators will be closed unless it has been discussed
in an issue and has a collaborator to champion the work.

## Requirements

All large pull requests must satisfy the following requirements in addition to
the standard [pull request requirements](./pull-requests.md).

### Detailed pull request description

The pull request description must provide sufficient context for reviewers
to understand the change. The description should explain:

* The motivation for the change.
* The high-level approach and architecture.
* Any alternatives that were considered and why they were rejected.
* How the change interacts with existing subsystems.

A thorough pull request description is sufficient. There is no requirement
to produce a separate design document, although contributors may choose to
link to a GitHub issue or other discussion where the design was developed.

### Review guide

The pull request description must include a review guide that helps reviewers
navigate the change. The review guide should:

* Identify the key files and directories to review.
* Describe the order in which files should be reviewed.
* Highlight the most critical sections that need careful attention.
* Include a testing plan explaining how the change has been validated and
  how reviewers can verify the behavior.

### Approval requirements

Large pull requests follow the same approval path as semver-major changes:

* At least **two TSC member approvals** are required.
* The standard 48-hour wait time applies. Given the complexity of large pull
  requests, authors should expect and allow for a longer review period.
* CI must pass before landing.

### Dependency changes

When a large pull request adds or modifies a dependency in `deps/`:

* Dependency changes should be in a **separate commit** from the rest of the
  pull request. This makes it easier to review the dependency update
  independently from the first-party code changes. When the pull request is
  squashed on landing, the dependency commit should be the one that carries
  the squashed commit message, so that `git log` clearly reflects the
  overall change.
* The provenance and integrity of the dependency must be verifiable.
  Include documentation of how the dependency was obtained and how
  reviewers can reproduce the build artifact.

## Avoiding large pull requests

Contributors should always consider whether a large pull request can be split
into smaller, independently reviewable pull requests. Strategies include:

* Landing foundational internal APIs first, then building on top of them.
* Landing refactoring or preparatory changes before the main feature.

Each pull request in a split series should remain self-contained: it should
include the implementation, tests, and documentation needed for that piece
to stand on its own.

### Strategies for reducing the review length in single pull requests

Large pull requests may involve a longer review process that becomes practically
impossible to track on GitHub due to UI limitations. These strategies help reduce
the review length in a single pull request.

* Open an issue first to confirm a substantial change is indeed desired in core
  to reduce lengthy discussions unrelated to the implementation in the pull request.
* Use proposal issues, RFCs, design documents, or other types of venues to
  explore high-level design and cross-cutting concerns.
* Keep the initial change provisional to reduce the thoroughness required in a
  single pull request. Gate premature changes behind build/runtime flags, or apply
  `dont-land-*` labels to avoid releasing the initial changes until it has been more
  thoroughly tested and iterated in follow-up pull requests.
* Leave non-blocking issues (e.g. stylistic preferences) to follow-up pull requests
  with a TODO comment in appropriate places.

### Feature forks and branches

For extremely large or complex changes that develop over time, such as adding
a major new subsystem, contributors should consider using a feature fork.
This approach has been used successfully in the past for subsystems like QUIC.

The feature fork must be hosted in a **separate GitHub repository**, managed
by the collaborator championing the change. The repository can live in the
[nodejs organization](https://github.com/nodejs) or be a personal repository
of the champion. The champion is responsible for coordinating development,
managing access, and ensuring the fork stays up to date with `main`.

A feature fork allows:

* Incremental development with multiple collaborators.
* Review of individual commits rather than one monolithic diff.
* CI validation at each stage of development.
* Independent issue tracking and discussion in the fork repository.

When the work is ready, the final merge into `main` via a pull request still
requires the same approval and review requirements as any other large pull
request.

## Guidance for reviewers

Reviewing a large pull request is a significant time investment. Reviewers
should:

* Read the pull request description and review guide before diving into the
  code.
* Focus review effort on `lib/` and `src/` changes, which have the highest
  impact on the runtime. `test/` and `doc/` changes, while important, are
  lower risk.
* Not hesitate to request that the author split the pull request if it can
  reasonably be broken into smaller pieces.
* Coordinate with other reviewers to divide the review workload when possible.