tomnomnom/gron · error

invalid value `%s`

Error message

invalid value `%s`

What it means

In ungronTokens, value tokens are decoded with encoding/json (with UseNumber). If json.Decode fails on the token's text, the token is not a valid JSON value and ungronTokens returns "invalid value `%s`" containing the offending text.

Source

Thrown at ungron.go:393

	}

	t := ts[0]
	switch {
	case t.isPunct():
		// Skip the token
		val, err := ungronTokens(ts[1:])
		if err != nil {
			return nil, err
		}
		return val, nil

	case t.isValue():
		var val interface{}
		d := json.NewDecoder(strings.NewReader(t.text))
		d.UseNumber()
		err := d.Decode(&val)
		if err != nil {
			return nil, fmt.Errorf("invalid value `%s`", t.text)
		}
		return val, nil

	case t.typ == typBare:
		val, err := ungronTokens(ts[1:])
		if err != nil {
			return nil, err
		}
		out := make(map[string]interface{})
		out[t.text] = val
		return out, nil

	case t.typ == typQuotedKey:
		val, err := ungronTokens(ts[1:])
		if err != nil {
			return nil, err
		}
		key := ""

View on GitHub (pinned to 88a6234ea2)

Solutions

1. Quote string values with double quotes: json.a = "hello";
2. Fix malformed numbers (no leading zeros beyond 0, no double dots, no NaN/Infinity)
3. Regenerate input via `gron` rather than writing statements by hand
4. Pre-validate each RHS value with json.Valid([]byte(value)) before ungron

Example fix

// before
json.a = 'hello';

// after
json.a = "hello";

value := `"hello"` // RHS text from the statement
if !json.Valid([]byte(value)) {
	// invalid JSON value; fix quoting/number before ungron
}

func isJSONValue(text string) bool {
	return json.Valid([]byte(text))
}

v, err := ungronTokens(ts)
if err != nil {
	if strings.HasPrefix(err.Error(), "invalid value `") {
		// quote strings / fix numeric literals, then retry
	}
	return err
}

When it happens

Trigger: `gron --ungron` on statements whose value tokens are not valid JSON — e.g. bare numbers like `json.a = 007;`, malformed numbers (`1.2.3`), unquoted bare words in value position, or text corrupted by shell/quoting.

Common situations: Hand-written gron statements where strings were not quoted; output mangled by sed removing quotes; gron statements produced by other tools with non-JSON literals (NaN, Infinity, single-quoted strings).

Related errors

• invalid JSON layout
• invalid statement
• failed to form statements: %s
• non-assignment statement
• statement has no value

AI-assisted analysis of tomnomnom/gron@88a6234ea2 (2026-09-06). Data as JSON: /api/errors/fccdb88c06717bdb. Report an issue: GitHub.