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A human-readable data serialization format. Popular for configuration files (Docker Compose, Kubernetes, CI/CD).
Clark Evans, Ingy dot Net, and Oren Ben-Kiki first proposed YAML in 2001, with the name originally standing for "Yet Another Markup Language" before being retronymed to "YAML Ain't Markup Language" to emphasize its data-oriented rather than document-oriented design. YAML uses indentation to represent hierarchy, making it visually clean and readable without the syntactic noise of braces and brackets. This readability made YAML the configuration format of choice for DevOps and cloud-native tooling: Docker Compose, Kubernetes manifests, GitHub Actions workflows, GitLab CI pipelines, Ansible playbooks, Helm charts, and CloudFormation templates all use YAML.
The format supports scalars (strings, numbers, booleans, null, dates), sequences (ordered lists), and mappings (key-value pairs), with anchors and aliases for referencing repeated structures. YAML is a superset of JSON — every valid JSON document is valid YAML — and includes additional features like multi-line strings (literal and folded), comments, and complex key types. The specification (currently YAML 1.2.2) defines a streaming model where a single file can contain multiple documents separated by --- markers.
YAML's implicit typing (the "Norway problem" where NO is parsed as false) and indentation sensitivity create well-known pitfalls, driving the development of strict YAML linters and the adoption of JSON Schema for YAML validation. The format's tree structure — mappings and sequences forming nested hierarchies — means that structural comparison provides better results than text diff, especially when indentation changes reformat content without altering semantics.
YAML's indentation-based hierarchy means that reformatting changes and semantic changes are hard to distinguish with plain text diff. Structural YAML comparison parses the document tree and compares values at each path, ignoring cosmetic reformatting while highlighting actual data changes.
Teams compare YAML to review Kubernetes manifest updates, verify CI/CD pipeline modifications, audit Helm chart value overrides, and validate Ansible playbook changes — all infrastructure-critical operations where understanding the precise semantic difference is essential for safe deployment.
UtraDiff builds a semantic tree from YAML files, handling indentation-based nesting and anchor/alias references in the tree diff. Reordered keys at any depth are detected as identical, filtering out noise from different serialization tools. Merged anchors are resolved before comparison so inherited values are diffed accurately.
The text diff with YAML syntax highlighting runs alongside the tree view. Cross-format comparison lets you diff YAML against JSON, TOML, INI, or .env files.
Supported extensions: .yml .yaml
YAML can be compared with: JSON, JSON5, JSONL, TOML, INI, Environment, Properties