Format Engine (fmt)¶

The format engine ensures consistent formatting across your Terraform and Terragrunt files.

Overview¶

The fmt engine uses the HCL formatter to standardize code formatting, similar to terraform fmt but with additional capabilities.

Usage¶

# Format all files
terratidy fmt

# Check formatting without changes
terratidy fmt --check

# Show colored diff of changes
terratidy fmt --diff

# Preview changes without modifying files
terratidy fmt --check --diff

# Format only changed files
terratidy fmt --changed

# Format and apply style fixes
terratidy fmt --all

# Check formatting and style without changes
terratidy fmt --all --check

# Preview all changes with diff
terratidy fmt --all --check --diff

fmt vs style --fix vs fmt --all¶

TerraTidy provides different commands for different formatting needs:

Command	HCL Formatting	Style Fixes	Use Case
`terratidy fmt`	✓		Standard formatting (whitespace, alignment)
`terratidy fmt --check`	check		Verify formatting without changes
`terratidy style --fix`		✓	Style fixes only (naming, block ordering)
`terratidy fmt --all`	✓	✓	Complete formatting and style fixes
`terratidy fmt --all --check`	check	check	Verify formatting and style without changes
`terratidy fix`	✓	✓	Same as `fmt --all` (alias)

fmt: Applies HCL formatting rules (indentation, alignment, spacing). This is equivalent to terraform fmt.
style --fix: Applies TerraTidy style rules (naming conventions, block ordering, file organization) without HCL formatting.
fmt --all: Combines both - first formats files, then applies style fixes. After the style pass, a final format pass re-runs to restore equal-sign alignment that style rewrites can disrupt (announced as Re-aligning attributes after style fixes...). See commands.md#terratidy-fmt for the full workflow.

Structured Output (`--format`)¶

fmt honours the global --format flag, which accepts text (default), table, json, json-compact, sarif, html, junit, markdown, or github. When --format is anything other than text, fmt suppresses its human-readable banners and progress lines and emits all findings — including fmt.needs-formatting and fmt.formatted — through the shared formatter at the end. The --all re-alignment pass still runs; only its progress text is suppressed. See commands.md#terratidy-fmt for examples.

Configuration¶

engines:
  fmt:
    enabled: true
    check: false  # Check mode - report but don't modify files
    diff: false   # Show diff of changes

Option	Type	Default	Description
`enabled`	bool	`true`	Enable/disable the format engine
`check`	bool	`false`	Check mode - report formatting issues without modifying files
`diff`	bool	`false`	Show colored unified diff of changes (can be combined with `check`)

What Gets Formatted¶

Indentation (2 spaces)
Attribute alignment
Block spacing
Trailing whitespace removal
Consistent line endings

Example¶

Before:

resource "aws_instance" "example" {
ami = "ami-12345"
  instance_type="t2.micro"
    tags={
Name="example"
  }
}

After:

resource "aws_instance" "example" {
  ami           = "ami-12345"
  instance_type = "t2.micro"
  tags = {
    Name = "example"
  }
}

Integration with CI/CD¶

Use --check in CI to fail if files need formatting:

- name: Check formatting
  run: terratidy fmt --check

Use --all --check to verify both formatting and style:

- name: Check formatting and style
  run: terratidy fmt --all --check