GitHub Actions "You have an error in your YAML syntax" (tab characters)

By Kaveh Alemi·Latchkey

YAML does not allow tab characters for indentation. A single tab pasted into a workflow file produces a parse error that points at a line and column.

What this error means

The workflow is rejected with a YAML syntax error at a specific line, and the offending indentation turns out to be a tab rather than spaces.

Invalid workflow file: .github/workflows/ci.yml
You have an error in your yaml syntax on line 9

Common causes

Tab used for indentation

An editor inserted a literal tab; YAML only permits spaces for indentation.

Mixed tabs and spaces

Copy-paste from another file can introduce tabs that break alignment.

How to fix it

Replace tabs with spaces

1. Show whitespace in your editor and convert tabs to two spaces.
2. Set the editor to insert spaces for .yml/.yaml files.
3. Re-indent the flagged line consistently.

# .editorconfig
[*.{yml,yaml}]
indent_style = space
indent_size = 2

How to prevent it

• Add an .editorconfig that enforces spaces for YAML.
• Run a YAML linter in pre-commit to catch tabs.

Frequently asked questions

Related guides

References

• GitHub Actions documentation
• Workflow syntax for GitHub Actions