YAML Validator Online — Free Syntax Checker

Validate Kubernetes manifests, Docker Compose, GitHub Actions, Helm charts, and Ansible YAML. Catch indentation, syntax, and duplicate-key errors instantly — 100% in your browser.

Input YAML

Validation Result

What is a YAML Validator?

A YAML validator parses YAML documents and reports any errors that would prevent a real YAML parser — kubectl, docker compose, ansible, or a CI/CD runner — from accepting the file. It catches indentation mistakes, missing colons, duplicate keys, tabs used instead of spaces, malformed lists, and unbalanced quotes before you push to production.

YAML's reliance on whitespace makes it powerful but fragile: a single misplaced space silently changes a document's structure. The OpenFormatter YAML validator runs entirely in your browser — no upload, no account, no rate limits — and is built for engineers who debug Kubernetes manifests, Docker Compose files, GitHub Actions workflows, Helm values.yaml, and Ansible playbooks every day.

How to validate YAML online — 4 steps

Paste your YAML. Copy a Kubernetes manifest, Compose file, or any .yaml source into the Input panel above. You can also click Load Sample to try a demo ConfigMap.
Click Validate. The validator parses the document client-side and either confirms it is well-formed or surfaces the exact error.
Read the error. Errors include the line number and the reason (e.g. Duplicate key "name" or Tabs are not allowed). Fix and re-run.
Copy the parsed JSON. On success, the validator shows the equivalent JSON tree so you can verify the structure your tooling will see.

YAML errors the validator catches

1. Tab indentation

YAML forbids tabs as indentation. Editors that auto-insert tabs cause silent failures.

# ❌ Invalid — uses a tab on line 2
server:
	port: 8080

# ✓ Valid — 2 spaces
server:
  port: 8080

2. Duplicate keys

Most YAML parsers accept duplicates silently and use the last value — a frequent source of production bugs.

# ❌ Invalid — port appears twice
service:
  port: 8080
  port: 9090   # silently overrides

# ✓ Valid — single port key
service:
  port: 8080

3. Wrong list-item indentation

Children of a list item must indent under the first character after the dash.

# ❌ Wrong — image is interpreted as a sibling of containers
containers:
  - name: web
  image: nginx

# ✓ Correct — image belongs to the list item
containers:
  - name: web
    image: nginx

Syntax Validation

Indentation consistency, colon spacing, list formatting, quote balance, and duplicate-key detection — all reported with the exact line.

Precise Error Location

Every error lists the line number and a one-line reason so you can jump back to your editor and fix it without guessing.

Client-Side Only

YAML is parsed in JavaScript inside your browser. Manifests with secrets, tokens, or proprietary config never leave the device.

Common use cases

check_circleValidating Kubernetes manifests before kubectl apply to avoid failed rollouts
check_circleChecking Docker Compose files (compose.yaml) before docker compose up
check_circleLinting GitHub Actions workflow YAML before pushing to trigger CI/CD
check_circleVerifying Ansible playbook syntax before running against production hosts
check_circleValidating Helm chart values.yaml before helm install or upgrade
check_circleCatching errors in CircleCI, GitLab CI, Bitbucket Pipelines, and Travis CI YAML
check_circleChecking Prometheus, Grafana, and Loki configuration files
check_circleValidating OpenAPI / Swagger specs written in YAML

Why client-side validation matters

DevOps engineers and platform teams routinely paste manifests that contain database URLs, JWT signing keys, OAuth client secrets, and cloud credentials. A traditional online validator that uploads YAML to a server is a security risk — and many companies forbid it outright. Because OpenFormatter validates entirely in JavaScript on your machine, no network request leaves the browser when you click Validate. Open DevTools → Network and verify it yourself.

Need to do more than validate?

Format, view, parse, or convert YAML with the rest of OpenFormatter's tools — all browser-side.

YAML Formatter YAML Viewer YAML to JSON

Frequently Asked Questions

What does a YAML validator check?

A YAML validator parses your document and reports syntax errors: inconsistent indentation, tabs used instead of spaces, missing colons, malformed sequences, duplicate keys at the same level, unbalanced quotes, and broken multi-line scalars. It does not validate semantic correctness against a schema (e.g. that a Kubernetes Pod has the right fields) — it confirms the document is well-formed YAML.

Why does my Kubernetes YAML fail validation when it looks correct?

Two common causes. First, mixed tabs and spaces — Kubernetes YAML must use spaces only. Second, indentation under a list item is one of the trickiest YAML rules: child keys under a "- name:" item must align under "name", not under the dash. Paste the file into the validator and it reports the exact line and reason.

Can it validate multi-document YAML files with --- separators?

Yes. Each document section between --- separators is validated independently, so an error in one document does not stop the others from being checked.

Does the validator check against a Kubernetes or Docker Compose schema?

No. This tool checks YAML well-formedness — that the syntax parses cleanly. Schema validation (e.g. confirming a Pod has the required containers field, or that compose.yaml uses a valid service key) requires kubectl --dry-run, kubeval, or docker compose config, which need the target schema definitions.

Why does YAML treat "yes" as a boolean?

YAML 1.1 treats unquoted yes, no, on, off, true, false as booleans. This is the famous Norway problem (the country code "NO" parsed as false). Quote the value ("yes") to keep it a string. Most modern parsers default to YAML 1.2, which only treats true/false as booleans, but many tools — including older Ansible and some k8s parsers — still use 1.1 semantics.

Is my YAML uploaded to your servers?

No. Validation runs entirely in your browser using JavaScript. Manifests containing secrets, tokens, database credentials, or proprietary configuration never leave your device. You can verify this in your browser DevTools Network tab — no requests are made when you click Validate.

How do I fix indentation errors in YAML?

Pick a single indent width (2 spaces is the Kubernetes/Docker convention) and use it consistently. Never mix tabs and spaces. Children of a key must indent more than the key itself. Children of a list item ("- ") must align under the first character after the dash, not under the dash.

What is the difference between YAML validation and YAML linting?

Validation checks that YAML is syntactically correct (parseable). Linting goes further — it checks style rules like maximum line length, key order, comment formatting, and trailing whitespace. This tool focuses on validation; for full linting use yamllint or a pre-commit hook.