# How to Contribute to the Abseil C++ Project: A Complete Guide > Learn how to contribute to the Abseil C++ project. Follow our guide to sign the CLA, meet priority criteria, adhere to the style guide, and submit tested pull requests on GitHub. - Repository: [Abseil/abseil-cpp](https://github.com/abseil/abseil-cpp) - Tags: how-to-guide - Published: 2026-07-19 --- **To contribute to Abseil C++, you must sign the Google Contributor License Agreement, propose changes that meet the project's priority criteria (such as widespread usage or high impact), follow the Google C++ Style Guide, and submit small, tested pull requests via GitHub.** Abseil C++ is Google's open-source library of C++ utilities that extend the standard library. While the project actively welcomes external contributions, the maintainers enforce a strict review process to ensure stability across the tens of thousands of projects that depend on this codebase. Learning how to contribute to the Abseil C++ project involves understanding the requirements documented in [`CONTRIBUTING.md`](https://github.com/abseil/abseil-cpp/blob/main/CONTRIBUTING.md) and preparing your development environment to run the comprehensive Bazel and CMake test suites. ## Sign the Contributor License Agreement (CLA) Before any code can be merged, every contributor must have a signed Contributor License Agreement on file at the Google CLA portal ([cla.developers.google.com](https://cla.developers.google.com/)). This is a one-time requirement per contributor that grants the project legal permission to use your submissions. Pull requests from authors without a signed CLA will be automatically blocked by the repository's CI checks. ## Choose Changes That Align with Project Priorities The Abseil team accepts additions only when they satisfy specific strategic criteria outlined in the **Priorities** section of [`CONTRIBUTING.md`](https://github.com/abseil/abseil-cpp/blob/main/CONTRIBUTING.md). Proposals that do not meet these standards will likely be rejected, so review these guidelines carefully before investing development time: - **Widespread usage** – Libraries already adopted by tens of thousands of internal Google projects - **Anticipated widespread usage** – APIs that fill gaps in the C++ standard and are likely to see broad adoption (e.g., `absl::from_chars`) - **High impact** – Utilities that solve significant runtime or development problems (e.g., `absl::FixedArray`) - **Support for a higher-priority library** – Internal helper libraries required by larger, more critical components If you are uncertain whether your feature fits these categories, open a proposal issue first using the [`ABSEIL_ISSUE_TEMPLATE.md`](https://github.com/abseil/abseil-cpp/blob/main/ABSEIL_ISSUE_TEMPLATE.md) to discuss the idea with maintainers. ## Follow the Google C++ Style Guide All submissions must strictly adhere to the **Google C++ Style Guide** available at [github.com/google/styleguide](https://github.com/google/styleguide). In addition to the general Google rules, Abseil enforces repository-specific conventions detailed in `CONTRIBUTING.md#coding-style`. These standards cover naming conventions, header file structure, include guards, and formatting requirements that keep the codebase consistent across modules like `absl/strings/`, `absl/container/`, and `absl/memory/`. ## Submit a Focused Pull Request Abseil requires small, atomic changes rather than large refactorings. Each pull request should contain **one logical change** with a clean commit history. Use interactive rebase (`git rebase -i upstream/master`) to squash fix-up commits and reorder your history into a coherent narrative. Your PR description must clearly explain **what** changed and **why**, and should reference any related issues. This approach allows reviewers to understand the context quickly and reduces the time to merge. ## Verify Your Changes with Local Testing The Abseil CI pipeline runs both Bazel and CMake builds across multiple platforms. You must verify your changes locally before requesting review to avoid CI failures. ### Running Bazel Tests Execute the full test suite (excluding performance benchmarks) from the repository root: ```bash bazel test --test_tag_filters="-benchmark" //... ``` For component-specific testing, target individual modules. For example, if modifying string utilities: ```bash bazel test //absl/strings:str_join_test ``` ### Using Docker CI Scripts On Linux, you can replicate the exact CI environment using the shell scripts in the `ci/` directory. These scripts handle environment setup automatically: ```bash # Example: Run Alpine Linux GCC CMake tests ./ci/linux_gcc_alpine_cmake.sh ``` Additional options are documented in [`ci/README.md`](https://github.com/abseil/abseil-cpp/blob/main/ci/README.md). ## Address Review Feedback and Merge Process Expect iterative feedback from maintainers and be prepared to revise your code promptly. Reviewers focus on API design, performance characteristics, and adherence to Abseil's compatibility guarantees. If a pull request stalls without activity for several weeks, maintainers may close it due to inactivity. ### Special Instructions for Googlers Google employees do not submit changes through the GitHub PR UI. Instead, Googlers submit modifications via internal Piper CLs (Google's internal version control system). The internal-to-external propagation system automatically syncs these approved changes to the public GitHub repository. ## Code Example: Adding a New Utility When contributing new functionality, place headers in the appropriate `absl/` subdirectory with proper include guards and comprehensive unit tests. Below is a simplified example of adding a string utility function in [`absl/strings/str_join.h`](https://github.com/abseil/abseil-cpp/blob/main/absl/strings/str_join.h): ```cpp // File: absl/strings/str_join.h #ifndef ABSL_STRINGS_STR_JOIN_H_ #define ABSL_STRINGS_STR_JOIN_H_ #include #include #include #include "absl/base/internal/throw_delegate.h" namespace absl { // Joins `parts` using `sep` and returns the concatenated string. inline std::string StrJoin(absl::Span parts, absl::string_view sep) { std::string result; for (size_t i = 0; i < parts.size(); ++i) { if (i != 0) result.append(sep); result.append(parts[i]); } return result; } // Overload accepting an initializer list. inline std::string StrJoin(std::initializer_list parts, absl::string_view sep) { return StrJoin(absl::MakeSpan(parts), sep); } } // namespace absl #endif // ABSL_STRINGS_STR_JOIN_H_ ``` Accompany your implementation with unit tests in `absl/strings/str_join_test.cc`: ```cpp #include "absl/strings/str_join.h" #include "gtest/gtest.h" TEST(StrJoinTest, Basic) { EXPECT_EQ(absl::StrJoin({"a", "b", "c"}, ","), "a,b,c"); } ``` Run the specific test target to verify correctness: ```bash bazel test //absl/strings:str_join_test ``` ## Summary - **Sign the CLA** once at cla.developers.google.com before your first contribution - **Validate your proposal** against the four priority categories (widespread usage, anticipated usage, high impact, or support for higher-priority libraries) - **Follow style guidelines** from the Google C++ Style Guide and repository-specific rules in [`CONTRIBUTING.md`](https://github.com/abseil/abseil-cpp/blob/main/CONTRIBUTING.md) - **Keep PRs focused** on single logical changes with clean git history - **Test locally** using `bazel test --test_tag_filters="-benchmark" //...` or the `ci/linux_*.sh` scripts - **Respond to feedback** promptly to keep the review process moving ## Frequently Asked Questions ### Do I need to sign a CLA for every contribution to Abseil C++? No, the Google Contributor License Agreement is required only once per contributor. After signing at cla.developers.google.com, your CLA status applies to all future contributions across Google open-source projects, including Abseil C++. Your GitHub username must be associated with the signed CLA for the automated checks to pass. ### What types of changes does the Abseil C++ project accept? Abseil accepts additions that demonstrate widespread current usage, anticipated widespread adoption (like standard library gap fillers), high impact on performance or developer productivity, or direct support for higher-priority libraries. The project does not accept experimental code or features with limited applicability. Check the **Priorities** section in [`CONTRIBUTING.md`](https://github.com/abseil/abseil-cpp/blob/main/CONTRIBUTING.md) before proposing new functionality. ### How do I run the test suite before submitting a pull request? You can verify your changes using Bazel with the command `bazel test --test_tag_filters="-benchmark" //...` from the repository root, which runs all tests except performance benchmarks. Alternatively, use the Docker-based scripts in the `ci/` directory (such as [`ci/linux_gcc_alpine_cmake.sh`](https://github.com/abseil/abseil-cpp/blob/main/ci/linux_gcc_alpine_cmake.sh)) to replicate the exact CI environment used by the project. ### Can Google employees submit changes through GitHub pull requests? No, Googlers must submit changes through internal Piper CLs rather than the GitHub pull request interface. Google internal changes propagate automatically to the public GitHub repository through the internal-to-external synchronization system. This process ensures that internal dependencies and security reviews are handled properly before code reaches the open-source branch.