What causes "failed to parse YAML in config file %s: %w" in wtfutil/wtf?

Open the file at the path named in the error and fix the YAML syntax at the line/column reported by the wrapped error

failed to parse YAML in config file %s: %w

Error message

failed to parse YAML in config file %s: %w

What it means

This error is returned by readQueryFileContent in modules/azurelogs/config.go:53 when yaml.Unmarshal fails to parse the contents of the query config file into the config struct. It wraps the underlying YAML error, so the wrapped message pinpoints the offending line/column. The library throws it because a malformed YAML file cannot be safely turned into a Session QueryFile.

Source

Thrown at modules/azurelogs/config.go:53

		sess.QueryFile = configFile
	} else {
		return fmt.Errorf("invalid query file format: %s, expected .yaml", filename)
	}

	return nil
}

// readQueryFileContent reads a single config file and returns a QueryFile struct
func readQueryFileContent(filePath string) (QueryFile, error) {
	var configFile QueryFile
	data, err := os.ReadFile(filePath)
	if err != nil {
		return configFile, fmt.Errorf("failed to read query config file %s: %w", filePath, err)
	}

	err = yaml.Unmarshal(data, &configFile)
	if err != nil {
		return configFile, fmt.Errorf("failed to parse YAML in config file %s: %w", filePath, err)
	}

	return configFile, nil
}

View on GitHub (pinned to bb838c1ccb)

Solutions

Open the file at the path named in the error and fix the YAML syntax at the line/column reported by the wrapped error
Validate the file with a YAML linter (e.g. yamllint or `python -c "import yaml,sys; yaml.safe_load(open(sys.argv[1]))" <file>`)
Replace tab characters with spaces for indentation
Quote values containing special characters like ':' or '#'

Example fix

// before (config.yml)
workspace:
	id: my-workspace  # tab indentation breaks YAML parser
// after
workspace:
  id: "my-workspace"  # spaces, quoted value

Defensive patterns

Strategy: validation

Validate before calling

data, err := os.ReadFile(queryPath)
if err != nil { return err }
var probe map[string]any
if err := yaml.Unmarshal(data, &probe); err != nil {
    return fmt.Errorf("invalid YAML in %s: %w", queryPath, err)
}

Try / catch

sess, err := azurelogs.Init(&queryPath)
if err != nil {
    var yamlErr error
    if errors.Unwrap(err) != nil { /* inspect wrapped cause */ }
    log.Fatalf("query config invalid: %v", err)
}

Prevention

Lint query YAML files in CI with yamllint before deployment
Use spaces, never tabs, for YAML indentation
Keep query files in version control so bad edits are caught in review
Add a unit test that unmarshals every shipped query file at build time

When it happens

Trigger: Calling Init/readQueryFile with a query file whose content is not valid YAML: bad indentation, tabs instead of spaces, missing colon after a key, duplicate keys, or YAML special characters unquoted. Also produced by yaml tags in the file not matching the struct (caught by TestQueryFile_YAMLTags).

Common situations: Hand-edited query config files with wrong indentation (tabs are illegal in YAML), copy-pasted config losing indentation, unquoted values containing ':' or '#', or a query path pointing to a JSON/other non-YAML file.

Understand the failure class

Parsing and encoding errors: unexpected token, malformed input — why parsers reject input and how to find the real culprit.

Related errors

AI-assisted analysis of wtfutil/wtf@bb838c1ccb (2026-09-03). Data as JSON: /api/errors/22212f7045b13280. Report an issue: GitHub.