FastFormat 1.5.0

FastFormat

A fast C# formatter that supports common formatting-related .editorconfig options. Designed for rapid development with format-on-save workflows.

FastFormat is not a replacement for dotnet format. It is a fast intermediary between no formatting and waiting several seconds for a full dotnet format run. Use it when you want formatting feedback quickly, then rely on dotnet format (or CI) for comprehensive validation.

Performance

benchmark.sh creates a synthetic C# project, builds FastFormat in Release mode, attempts a NativeAOT publish, then compares against dotnet format.

The benchmark covers four runs:

If the NativeAOT publish succeeds and the published binary passes a smoke formatting run, the output includes a NativeAOT column. Current Roslyn Workspaces dependencies publish with AOT warnings but fail the smoke run, so NativeAOT is not enabled for packaging yet.

Caveats: this is a synthetic corpus, not a substitute for benchmarking your real solution. dotnet format does MSBuild workspace loading and broader analysis; FastFormat intentionally skips that work to be a fast format-on-save/intermediate formatter.

Run it yourself:

./benchmark.sh 100 200
./benchmark.sh --verbose 200 500 5

Installation

dotnet tool install --global FastFormat

Usage

# Format files or directories
# (refuses to run on non-project directories without --force)
dotnet-fastformat src/
dotnet-fastformat Program.cs

# Check formatting without making changes
dotnet-fastformat --check src/

# Include/exclude patterns
dotnet-fastformat --exclude "**/*.generated.cs" src/
dotnet-fastformat --include "src/**/*.cs" --include "tests/**/*.cs" .

# Bypass the project-directory safety check
dotnet-fastformat --force ~/some-random-dir/

# Stdin -> stdout
cat Program.cs | dotnet-fastformat
cat Program.cs | dotnet-fastformat --stdin-filepath src/Program.cs

# Long-running stdio LSP mode for editor format-on-save
dotnet-fastformat --lsp

# Verbose output
dotnet-fastformat -v src/

# Control parallelism
dotnet-fastformat -p 8 src/

LSP Mode

dotnet-fastformat --lsp starts a stdio Language Server Protocol server. It advertises full-document sync, textDocument/formatting, and textDocument/rangeFormatting, so editors can keep one FastFormat process alive and avoid paying Roslyn startup on every save.

LSP mode never writes files directly. It returns TextEdit[] responses to the editor and uses file:// document URIs for .editorconfig resolution. Full-document formatting integrates with the existing .git/fastformat-cache: if the current document hash is known to be formatted, FastFormat returns no edits without invoking Roslyn. The server also keeps a bounded in-memory cache for repeated formatting requests during the same session.

Supported .editorconfig Options

• indent_style
• indent_size
• tab_width
• end_of_line
• insert_final_newline
• trim_trailing_whitespace
• csharp_new_line_before_open_brace
• csharp_new_line_before_catch
• csharp_new_line_before_else
• csharp_new_line_before_finally
• csharp_new_line_before_members_in_object_initializers
• csharp_new_line_between_query_expression_clauses
• dotnet_sort_system_directives_first
• dotnet_separate_import_directive_groups

File Types

• .cs — C# source files
• .csx — C# script files

Safety

When run on a directory, FastFormat refuses to recurse unless the directory (or an ancestor) looks like a project — indicated by the presence of .git, .editorconfig, *.csproj, *.sln, or *.slnx. It also refuses to run directly on $HOME or the filesystem root. Use --force to bypass this check.

Encoding

Files are read and written preserving their existing BOM. Files without a BOM are assumed to be UTF-8.

Default Behaviors

• Final newline: Files are always given a trailing newline unless .editorconfig explicitly sets insert_final_newline = false.

Why is it faster?

• No MSBuild workspace loading
• No semantic analysis
• Parallel file processing
• Direct .editorconfig parsing without heavy workspace machinery
• Gitignore-aware file discovery