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libyaml

The fast C library that forms the foundation of many YAML implementations.

Overview

libyaml is a YAML parser and emitter written in C. It's designed for speed and efficiency, and serves as the foundation for YAML libraries in many programming languages.

Why libyaml Matters

Foundation Layer

libyaml provides the parsing engine for:

  • pyyaml (Python) - Via C extension
  • Ruby YAML (Psych) - Ruby's standard YAML library
  • Perl YAML (YAML::XS) - High-performance Perl YAML
  • PHP yaml extension - PHP's native YAML support
  • Many other language bindings

Performance Critical

  • Written in C for maximum speed
  • Minimal memory footprint
  • Suitable for embedded systems
  • Optimized for high-throughput applications

YAML Specification Reference

  • Comprehensive YAML 1.1 implementation
  • Reference for implementers
  • Extensive test suite
  • Standards-compliant

YAML LLC Maintenance

Under YAML LLC's stewardship, libyaml receives:

Security First

  • Regular security audits
  • Memory safety improvements
  • Rapid vulnerability patching
  • Fuzzing and security testing
  • YES members get 48-hour early CVE notifications

Active Development

  • Bug fixes and stability improvements
  • Performance optimizations
  • YAML 1.2 specification support
  • Compiler and platform compatibility

Professional Support

  • Responsive to issues and pull requests
  • Clear development roadmap
  • Support for library consumers
  • Integration guidance

Maintenance & Accountability

libyaml is professionally maintained by YAML LLC, led by Ingy döt Net, co-creator of YAML.

  • Security contact: security@yaml.com
  • Disclosure policy: Coordinated disclosure with advance notice to YES members
  • Release cadence: Security patches prioritized, feature releases quarterly

Need supply chain documentation for compliance? Learn about the YES Program →

Technical Details

Features

  • Full YAML 1.1 support (1.2 in progress)
  • Event-based (SAX-like) parsing
  • Streaming API for large documents
  • Low memory footprint
  • No external dependencies
  • Cross-platform compatibility

Architecture

libyaml provides two APIs:

Parser API (Low-level): 

yaml_parser_t parser;
yaml_event_t event;

yaml_parser_initialize(&parser);
yaml_parser_set_input_file(&parser, file);

while (yaml_parser_parse(&parser, &event)) {
    // Process events
    yaml_event_delete(&event);
}

Emitter API (Output): 

yaml_emitter_t emitter;
yaml_event_t event;

yaml_emitter_initialize(&emitter);
yaml_emitter_set_output_file(&emitter, file);

// Emit events
yaml_emitter_emit(&emitter, &event);

Performance

  • Optimized C implementation
  • Minimal memory allocations
  • Suitable for resource-constrained environments
  • Handles multi-GB documents efficiently

Use Cases

Language Bindings

Many languages use libyaml for performance:

# Python with C acceleration
import yaml

# Automatically uses libyaml if available
data = yaml.safe_load(input)

Embedded Systems

libyaml's small footprint makes it ideal for embedded use:

  • IoT devices
  • Network equipment
  • Mobile applications
  • Resource-constrained environments

High-Performance Applications

Applications needing fast YAML parsing:

  • Log processors
  • Configuration systems
  • Data pipelines
  • Real-time systems

Language Bindings

libyaml has official and community bindings for:

Language Binding Status
Python pyyaml (C extension) Official
Ruby Psych Official
Perl YAML::XS Community
PHP yaml extension Community
Lua lua-yaml Community

Security

libyaml is regularly tested for security:

  • Continuous fuzzing with OSS-Fuzz
  • Static analysis
  • Memory safety testing (Valgrind, AddressSanitizer)
  • Security-focused code reviews

Recent security improvements:

  • Bounds checking
  • Integer overflow protection
  • Memory leak fixes
  • Stack limit enforcement

Support libyaml

libyaml is maintained through the YES Program. YES members get:

  • Priority support for libyaml issues
  • Early notification of security vulnerabilities
  • Influence over roadmap and feature development
  • Direct access to maintainers

Join the YES Program →

Resources