Workflow Integration

After installation, you can run slang-format directly, add it to a commit hook or CI job, or embed the formatter in another application.

Format your project

Format all Verilog and SystemVerilog files in the directory in place:

slang-format -i rtl/

This collects .sv, .svh, .v, and .vh files. Each file uses the nearest .slang/format.json found by searching its parent directories, with the current directory as a fallback. Nested configs replace parent configs; omitted settings use defaults.

To use the same settings across local commands, commit hooks, and CI, put .slang/format.json at your repository root. For example:

{
  "columnLimit": 100,
  "indentWidth": 4
}

Directory collection respects excludeDirectoryNames. To select particular files or subdirectories when formatting the project root, set projectPaths in that config and run slang-format -i .. See the configuration reference for details.

pre-commit and prek

Install slang-format on your PATH, then add this local hook to your .pre-commit-config.yaml:

repos:
  - repo: local
    hooks:
      - id: slang-format
        name: slang-format
        entry: slang-format
        language: system
        args: [-i]
        files: '\.(sv|svh|v|vh)$'

If you already have a repos list, append the hook's repo: local entry to it. Enable the hook and format existing files with:

pre-commit install
pre-commit run slang-format --all-files

prek users can replace pre-commit with prek in these commands. The hook uses your installed binary; it does not download or build slang-format.

On commit, pre-commit passes matching staged filenames to slang-format in batches. Each invocation can format multiple files, resolving .slang/format.json separately for each one. Review and stage any formatting changes, then retry the commit. Use the hook's files and exclude patterns to restrict which files are passed; projectPaths controls directory traversal, not explicit filenames.

The hook omits --strict: input structural errors, syntax-preservation failures, and idempotency failures leave the affected files unchanged without failing the hook. Other errors, including invalid configuration, file I/O errors, merge conflicts, failed reparsing, and internal errors, still fail it. See validation for the full output and exit-status policy.

Check formatting in CI

Install the same formatter version used locally, then run:

slang-format --check rtl/

--check leaves files unchanged and exits with status 1 if a file needs formatting, fails validation, or cannot be processed. Use this when CI should enforce both formatting and validation. --dry-run previews formatting changes but does not fail just because formatting would change a file.

To use the pre-commit hook in check-only mode, replace args: [-i] with args: [--check] and run pre-commit run slang-format --all-files in CI.

Use stdin in scripts

Pass source on stdin and read formatted source from stdout:

slang-format --assume-filename rtl/top.sv - < input.sv > formatted.sv

--assume-filename provides the path used for config discovery and diagnostics; it does not read that file. Without it, stdin uses the current directory's config. See the command reference for more options.

Embedding

Add slang-format as a subdirectory and link against the slang::format CMake target to format SystemVerilog in-process:

set(SLANG_FORMAT_BUILD_CLI OFF)
set(SLANG_FORMAT_INCLUDE_TESTS OFF)
set(SLANG_FORMAT_INCLUDE_INSTALL OFF)
add_subdirectory(external/slang-format)
target_link_libraries(my_tool PRIVATE slang::format)

A parent project that already defines compatible slang::slang and reflectcpp::reflectcpp targets can reuse them. Otherwise, the formatter uses its vendored slang and reflect-cpp submodules.

Config discovery and JSON parsing are part of the same formatter library, so embedded and standalone callers use identical behavior. See configuration for the available settings.