fy

Fast YAML command-line processor with validation and linting. Built on fast-yaml for high-performance YAML 1.2.2 processing.

Installation

From crates.io

cargo install fast-yaml-cli

[!TIP] Use cargo binstall fast-yaml-cli for faster installation without compilation.

From source

git clone https://github.com/bug-ops/fast-yaml
cd fast-yaml
cargo install --path crates/fast-yaml-cli

Verify installation

fy --version
fy --help

Usage

fy [OPTIONS] [FILE] <COMMAND>

Parse and validate

# Parse from file
fy parse config.yaml

# Parse from stdin
echo "name: test" | fy parse

# Show parse statistics
fy parse --stats large.yaml

Format YAML

Single file:

# Format to stdout
fy format messy.yaml

# Custom indentation (2-8 spaces)
fy format --indent 4 --width 100 config.yaml

# Format in-place
fy format -i config.yaml

Batch mode (directories, globs, multiple files):

# Format entire directory (recursive)
fy format -i src/

# Format with glob pattern
fy format -i "configs/**/*.yaml"

# Multiple files
fy format -i file1.yaml file2.yaml file3.yaml

# Non-recursive directory formatting
fy format -i --no-recursive configs/

# Parallel processing with 8 workers
fy format -i -j 8 large-project/

# Read file paths from stdin
find . -name "*.yaml" | fy format -i --stdin-files

[!TIP] Batch mode automatically detects when processing multiple files, directories, or glob patterns. Use -j N to control parallelism (default: auto-detect CPU cores).

Include/exclude patterns:

# Format all YAML except tests
fy format -i --exclude "**/tests/**" configs/

# Format only production configs
fy format -i --include "prod-*.yaml" configs/

# Combine patterns (respects .gitignore by default)
fy format -i --include "*.yaml" --exclude "draft-*" ./

Dry run and output control:

# Preview changes without modifying files
fy format -n configs/

# Quiet mode (only show errors)
fy format -i -q large-project/

# Verbose mode (show each file processed)
fy format -i -v configs/

Convert formats

# YAML to JSON
fy convert json config.yaml > config.json

# JSON to YAML
fy convert yaml data.json > data.yaml

# Compact JSON (no pretty-print)
fy convert json --pretty=false app.yaml

Lint YAML

# Lint with default rules
fy lint config.yaml

# Custom rules
fy lint --max-line-length 100 --indent-size 2 app.yaml

# JSON output for IDE integration
fy lint --format json config.yaml

Commands

Options

Common Options

Batch Mode Options

[!NOTE] Batch mode activates automatically when processing multiple paths, directories, glob patterns, or when using --stdin-files, --include, --exclude, or --jobs.

Features

Build with minimal features:

cargo build --release --no-default-features

[!NOTE] The linter feature adds the lint command. Without it, only parse, format, and convert are available.

Exit Codes

Examples

Pipeline usage

# Validate all YAML files
find . -name "*.yaml" -exec fy parse {} \;

# Format and convert in one pipeline
cat config.yaml | fy format | fy convert json > config.json

# Check YAML before committing
git diff --name-only --cached -- '*.yaml' | xargs -I {} fy lint {}

CI/CD integration

# GitHub Actions
- name: Validate YAML
  run: |
    cargo install fast-yaml-cli
    find . -name "*.yaml" -exec fy lint {} \;

Performance

Built on fast-yaml-core for optimal performance:

• Startup time: ~5ms
• Binary size: ~1MB (stripped)
• Batch processing: Multi-threaded with automatic CPU detection
• Streaming: Memory-mapped I/O for files >512KB
• Full YAML 1.2.2 compliance

[!TIP] Batch mode provides 3-6x speedup on multi-core systems when processing 100+ files. Use -j N to control worker count.

License

Licensed under MIT or Apache-2.0 at your option.