hashicorp/nomad · error

error unmarshaling json: %w

Error message

error unmarshaling json: %w

What it means

In `nomad var put` with `-in=json` (or a .json spec file), makeVariable unmarshals the file contents into api.Variable. If the bytes are not valid JSON, or do not match the expected Variable schema (e.g. top-level not an object, wrong types for fields), json.Unmarshal fails and the error is wrapped as `error unmarshaling json: <detail>`.

Source

Thrown at command/var_put.go:423

}

// makeVariable creates a variable based on whether or not there is data in
// content and the format is set.
func (c *VarPutCommand) makeVariable(path string) (*api.Variable, error) {
	var err error
	out := new(api.Variable)
	if len(c.contents) == 0 {
		out.Path = path
		out.Namespace = c.Meta.namespace
		out.Items = make(map[string]string)
		return out, nil
	}

	switch c.inFmt {
	case "json":
		err = json.Unmarshal(c.contents, out)
		if err != nil {
			return nil, fmt.Errorf("error unmarshaling json: %w", err)
		}
	case "hcl":
		out, err = parseVariableSpec(c.contents, c.verbose)
		if err != nil {
			return nil, fmt.Errorf("error parsing hcl: %w", err)
		}
	case "":
		return nil, errors.New("format flag required")
	default:
		return nil, fmt.Errorf("unknown format flag value")
	}

	// It is possible a specification file was used which did not declare any
	// items. Therefore, default the entry to avoid panics and ensure this type
	// of use is valid.
	if out.Items == nil {
		out.Items = make(map[string]string)
	}

View on GitHub (pinned to 482b49bf1a)

Solutions

1. Validate the file with `jq . file.json` (or a JSON linter) and fix syntax errors — comments and trailing commas are not allowed.
2. Ensure the root of the document is a JSON object matching the Variable schema (keys like `path`, `items`, `create_index`).
3. If the content is HCL, switch the flag: `nomad var put -in=hcl @file`.
4. Generate a correct skeleton with `nomad var init` and edit from there.

Example fix

// before (invalid: trailing comma)
{ "path": "app/config", "items": { "k": "v", }, }
// after
{ "path": "app/config", "items": { "k": "v" } }

var v any
if err := json.Unmarshal(data, &v); err != nil {
    return fmt.Errorf("spec is not valid JSON: %w", err)
}
if _, ok := v.(map[string]any); !ok {
    return fmt.Errorf("spec root must be a JSON object")
}

func isJSONObject(data []byte) bool {
    var v map[string]any
    return json.Unmarshal(data, &v) == nil && v != nil
}

if err := run(); err != nil {
    var uerr *json.UnmarshalTypeError
    if errors.As(err, &uerr) {
        log.Fatalf("field %s: expected %s", uerr.Field, uerr.Type)
    }
    log.Fatal(err)
}

When it happens

Trigger: `nomad var put ... -in=json @file` where the file contains truncated JSON, JSON5/HCL-style comments, trailing commas, a bare string/array at root, or field types that do not match api.Variable (e.g. `create_index` as a string instead of an int).

Common situations: Hand-edited spec files left with a trailing comma; exporting from another tool that emits YAML but naming the file .json; template-rendered JSON that failed to render valid output; copying an HCL example into a .json file.

Understand the failure class

Background: JSON parse error: "Unexpected token" / "not valid JSON" / "failed to parse" — what JSON parsers are really complaining about — this error's family across 45 libraries.

Related errors

• format error: %v
• A template must be supplied using '-template' when using go-
• Invalid value for "-out"; valid values are [go-template, hcl
• Error listing host volumes
• -node or -node-pool options can only be used when no ID is p

AI-assisted analysis of hashicorp/nomad@482b49bf1a (2026-09-04). Data as JSON: /api/errors/b15f47a9580d3f3f. Report an issue: GitHub.