YAML Validate — Free Online Tool

A YAML validator checks whether YAML is syntactically valid and helps you avoid whitespace-driven outages. It catches indentation mistakes, malformed lists/maps, invalid scalars, and duplicate keys. Developers use it for CI pipelines, Kubernetes manifests, and app configuration files. SWEDevTools: Prism validates locally in your browser for fast troubleshooting without uploading internal configs.

Features

• Indentation-aware parsing: Finds common errors like 'mapping values are not allowed here' caused by indentation mistakes.
• Kubernetes and CI friendly: Ideal for validating manifests and pipelines before apply/push.
• Local-first privacy: Validate internal deployment configs without uploading them to external YAML tools.
• Fast troubleshooting loop: Paste, validate, fix - optimized for triage when deployments or pipelines break.

Frequently Asked Questions

Why is YAML so easy to break?

YAML uses indentation to represent structure. One extra space can change nesting or make a value appear in the wrong context.

Are tabs allowed for indentation?

Generally no. Use spaces. Tabs frequently cause parsing failures across YAML tooling.

What is the difference between YAML and JSON?

YAML can be more human-friendly, but JSON has stricter syntax and fewer indentation pitfalls.

Why do numbers become strings (or vice versa)?

YAML has implicit typing. Quote values when the type matters (for example, '00123' should remain a string).

Are duplicate keys allowed?

Many parsers treat duplicate keys as errors or allow later values to override earlier ones. Avoid duplicates to prevent surprising behavior.

Why is my Kubernetes manifest invalid even when YAML is valid?

YAML validation checks syntax only. Kubernetes also enforces schema rules for apiVersion/kind/spec.

Should I use block scalars (| and >)?

They are great for multiline strings like scripts or certificates. Keep indentation consistent to avoid changing the resulting content.

How can I make YAML changes safer in PRs?

Use an editor with YAML support, keep indentation consistent, and validate both templates and rendered outputs before merging.

What happened to smalldev.tools?

smalldev.tools is no longer available. Prism by SWEDevTools offers the same developer tools and more, with offline support, pipeline chaining, and completely free usage — no signup required.

Is Prism a good alternative to onlineyamltools.com?

Yes. Prism processes YAML entirely in your browser with offline support, no ads, and pipeline chaining. Your configuration data stays completely private — nothing is uploaded to any server.