📄 YAML Formatter & Converter
Format YAML ↔ JSON - Validate syntax - runs in your browser
{
"name": "myapp",
"version": "1.0",
"services": {
"web": {
"image": "nginx:latest",
"ports": {}
},
"db": {
"image": "postgres:15",
"environment": {
"POSTGRES_PASSWORD": "secret"
}
}
}
}📊 Key Data Points
js-yaml
Full YAML 1.2 parser — same library used by many Node.js tools
yes becomes true
YAML 1.1 boolean gotcha — bare yes/no/on/off parse as booleans
Tabs forbidden
YAML prohibits tab characters for indentation — spaces only
YAML Formatter & Validator -- Complete USA Guide 2026
YAML is the configuration language of modern infrastructure — Kubernetes manifests, GitHub Actions workflows, Docker Compose files, Ansible playbooks. But YAML is famously finicky: a single inconsistent indentation or missing colon silently produces a valid-but-wrong parse.
This formatter validates and re-indents YAML using consistent rules. Runs entirely in your browser.
**Long-tail searches answered here:** validate Kubernetes YAML online without uploading, YAML indentation fixer free browser tool, YAML to JSON converter to check structure.
For infrastructure config, pair with TOML Formatter or Docker Compose Generator.
🔬 How This Calculator Works
Parses YAML using js-yaml running in the browser. Parsing converts YAML to a JavaScript object tree catching syntax errors including bad indentation, duplicate keys, and type coercion issues.
The formatter serializes back to YAML with consistent 2-space indentation. The JSON view converts the parsed object to formatted JSON, making it easy to inspect the actual data structure your YAML parser will produce. Common gotcha: yes parses as boolean true, no as false, and unquoted port numbers as integers.
✅ What You Can Calculate
Indentation normalization
Re-indents with consistent 2-space or 4-space indentation, eliminating mixed-tabs-and-spaces problems that cause cryptic parse failures.
YAML to JSON view
See what your YAML actually parses to as a JSON object. Catches gotchas like yes parsing as boolean true and unquoted strings being misinterpreted.
Inline vs block style toggle
Convert between block multi-line and inline flow YAML styles. Useful for compacting short sequences or expanding minified YAML configs.
Duplicate key detection
YAML technically allows duplicate keys but most parsers take the last value silently — this formatter catches them and warns before they cause hard-to-debug config behavior.
🎯 Real Scenarios & Use Cases
Debugging Kubernetes manifests
A Kubernetes deployment YAML fails with a vague error. Paste here to find the indentation problem or the missing field that is causing kubectl to reject it.
Validating GitHub Actions workflows
GitHub Actions workflows fail silently on malformed YAML. Validate the structure here before pushing — the JSON view shows exactly what GitHub parser will see.
Writing Docker Compose files
Pair with Docker Compose Generator — generate the base config there, then format and validate the YAML here before deploying.
Fixing CI/CD pipeline configs
CircleCI, GitLab CI, and Bitbucket Pipelines configs are all YAML. A missing colon or wrong indentation level breaks the whole pipeline.
💡 Pro Tips for Accurate Results
The JSON view is your best debugging tool. If you are unsure whether your YAML will parse correctly, check the JSON view. yes becoming true, 1.0 becoming 1, and bare strings being quoted are all immediately visible.
Kubernetes indentation rules. Kubernetes YAML uses 2-space indentation consistently. A single field indented 3 spaces instead of 2 produces a valid YAML parse but an incorrect Kubernetes object structure.
Quote strings that look like other types. Version numbers like 1.0, port strings like 80, and yes/no values should be quoted if you intend them as strings.
Diff before deploying. After editing a YAML config, use Diff Checker to compare old and new versions before applying changes to production.
🔗 Use These Together
🏁 Bottom Line
YAML ambiguities cause silent configuration bugs. This formatter surfaces those ambiguities by showing the actual parsed object as JSON.
For infrastructure workflows: generate base configs with Docker Compose Generator, format and validate here, then diff changes with Diff Checker.
Why is YAML so error-prone and what are the most common mistakes?
YAML's use of indentation for structure makes it visually clean but fragile. Most common mistakes: (1) Mixing tabs and spaces — YAML strictly forbids tabs for indentation; all indentation must use spaces. (2) Off-by-one indentation — a key indented one space too few or many changes the entire structure silently. (3) Unquoted special values — yes, no, true, false, null, and numbers are interpreted as booleans, nulls, and numbers in YAML 1.1; quote them if you need the literal string value. (4) Multiline strings — the literal block scalar (|) and folded scalar (>) have different behavior with trailing newlines.
What is the difference between YAML block style and flow style?
Block style uses newlines and indentation: each item on its own line. Flow style uses JSON-like inline syntax with {} for mappings and [] for sequences. A YAML file can mix both: a block mapping may contain flow-style lists as values. The formatter outputs block style as the primary format since it is more readable. Flow style is useful for short inline arrays: tags: [web, api, v2] is more compact than three lines of block-style list items.
How do I represent multiline strings in YAML?
Two syntaxes: the literal block scalar (|) preserves newlines exactly as written. The folded block scalar (>) converts single newlines to spaces and preserves blank lines as newlines. Example: description: | with text below produces a string with actual newlines preserved. The same with > folds single newlines to spaces. Add - (like |-) to strip the final newline. Add + (like |+) to keep all trailing newlines. Use | for SQL, shell scripts, and content where newlines matter; use > for long prose descriptions.
What are YAML anchors and aliases?
Anchors (&name) mark a node for reuse. Aliases (*name) reference a previously defined anchor. This is YAML's built-in DRY mechanism: define common config once and reference it multiple times. Example in Docker Compose: x-common: &common followed by environment settings, then use <<: *common under each service to merge the common configuration. The << key is a YAML merge key. Anchors reduce duplication in large Kubernetes manifests where many jobs share identical environment variables.
Why does my YAML validate here but fail in Kubernetes or Docker?
Standard YAML validation checks syntax and structure. Kubernetes and Docker Compose also validate against their specific schemas — the allowed fields, value types, and required keys for each resource kind. A valid YAML file can fail Kubernetes validation because: a field name has a typo (apiVersion: apps/v2 instead of apps/v1), a value has the wrong type (replicas: '3' is a string but Kubernetes requires an integer), or a required field is missing. Use kubectl apply --dry-run=client or docker compose config to validate against the application schema after YAML syntax validation passes.
How do I convert between YAML and JSON?
YAML is a superset of JSON — any valid JSON is valid YAML. Converting JSON to YAML just means reformatting to block style. Converting YAML to JSON loses YAML-specific features like comments and anchors. This tool handles both directions. The most common real-world use: Kubernetes objects are typically written as YAML but the API accepts JSON. When you need to convert a Kubernetes manifest for an API call, convert YAML to JSON here, then use the JSON Formatter to clean it up.
What other config file tools are on this site?
The JSON Formatter handles the JSON side of YAML-to-JSON conversions. The TOML Formatter covers the third major configuration format used by Cargo.toml and pyproject.toml. The Diff Checker is particularly useful for comparing two versions of a Kubernetes manifest or Docker Compose file before deploying changes. The Docker Compose Generator creates docker-compose.yml files alongside YAML app configs. All are in the Dev Tools section.