Knowledge base — Definition
YAML
Learn YAML for web development. Understand YAML syntax, configuration files, data serialization, and how YAML integrates with modern web development workflows.
What Is YAML?
YAML (YAML Ain’t Markup Language) is a human-readable data serialization format used extensively in web development, configuration files, and DevOps workflows. Unlike JSON or XML, YAML prioritizes readability with its clean, indentation-based syntax. For Toronto businesses working with modern web technologies, understanding YAML is essential for managing WordPress configurations, CI/CD pipelines, and deployment settings.
YAML Syntax Basics
Key-Value Pairs
YAML uses simple key-value pairs with colons. The key comes first, followed by a colon and space, then the value. Indentation (spaces, not tabs) defines structure and hierarchy. This makes YAML significantly more readable than JSON for configuration files.
Lists and Arrays
Lists in YAML use hyphens for each item. Nested lists use additional indentation. This format is commonly used for defining multiple values like server configurations, allowed domains, or deployment targets.
Multi-Line Strings
YAML supports several formats for multi-line content. The pipe character (|) preserves line breaks and trailing newline, while the greater-than sign (>) folds lines into a single line with spaces. These are useful for embedding scripts, HTML content, or long descriptions within configuration files.
Common Uses in Web Development
WordPress Configuration
Modern WordPress development tools use YAML for configuration. WP-CLI accepts YAML configuration files, and tools like Bedrock and Trellis use YAML for environment-specific settings. If you’re working with advanced WordPress deployment workflows, YAML configuration is part of the toolchain.
CI/CD Pipelines
GitHub Actions, GitLab CI, and CircleCI all use YAML to define build and deployment pipelines. These configuration files specify when to run tests, how to build assets, and where to deploy. Understanding YAML syntax is essential for automating your deployment process and maintaining reliable release workflows.
Docker and Containers
Docker Compose uses YAML (docker-compose.yml) to define multi-container applications. A single YAML file can describe your entire application stack — web server, database, caching layer — and bring it all up with one command. This simplifies local development and ensures consistency across environments.
YAML vs JSON vs XML
- YAML — Most readable, supports comments, best for configuration files written by humans
- JSON — Most widely supported, best for data exchange between systems and APIs
- XML — Most structured with schema validation, best for documents and complex data hierarchies
Choose YAML for configuration, JSON for API data exchange, and XML for document markup. Most modern web projects use a combination of all three.
Frequently Asked Questions
What does YAML stand for?
YAML is a recursive acronym that stands for “YAML Ain’t Markup Language.” The original meaning was “Yet Another Markup Language,” but it was changed to emphasize that YAML is a data serialization format, not a markup language like HTML or XML.
Is YAML the same as JSON?
No, though they’re related. JSON is a subset of YAML — any valid JSON is also valid YAML. However, YAML supports features JSON doesn’t, including comments, multi-line strings, and anchors for reusing content. YAML is better for human-written configuration; JSON is better for machine-to-machine data exchange.
Why does YAML care about indentation?
YAML uses indentation to define structure instead of brackets or tags. This makes it highly readable but means incorrect indentation causes errors. Always use spaces (not tabs) for YAML indentation, and be consistent with your indentation level throughout the file.
Related Resources
Further reading: YAML specification — YAML.org.