karatelabs/karate · error

Invalid number: missing exponent digits

Error message

Invalid number: missing exponent digits

What it means

JSON syntax error in parseNumber: an 'e'/'E' exponent marker was found but no digits followed (optionally after a sign), so the number literal is invalid. Fires on input like '1e' or '1e+'; add the exponent digits.

Solutions

1. Complete the exponent with its digits: '1e' -> '1e0', '2.5E-' -> '2.5E-1'.
2. Verify the source payload is not being truncated (increase buffer/response size limits).
3. Use plain decimal notation if the exponent is not needed.
4. Run the payload through a strict JSON validator before parsing to localize the fault.

Example fix

// before
String json = "{\"atoms\": 6.02e}";
// after
String json = "{\"atoms\": 6.02e23}";

// detect exponents without digits before parsing
if (json.matches(".*[eE][-+]?([^0-9]|$).*")) {
    throw new IllegalArgumentException("JSON number has an exponent with no digits");
}

// Java
try {
    Json json = Json.of(raw);
} catch (Exception e) {
    if (String.valueOf(e.getMessage()).contains("missing exponent digits")) {
        raw = raw.replaceAll("([eE][-+]?)\\s*(?=[,}\\]]|$)", "${1}0");
    } else { throw e; }
}

When it happens

Trigger: Parsing JSON with scientific-notation numbers truncated after 'e' or 'e-' — e.g. '[1e]', '{"v": 3e,}', or strings cut off mid-token by fixed-size buffers or streaming limits.

Common situations: Cut-and-paste from scientific output where the exponent was on the next line; truncated HTTP responses; hand-typed values like '1e9' with the '9' accidentally deleted.

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

• Invalid number: bare '-'
• Invalid number
• Invalid number: missing fraction digits
• Unexpected token ' ' in JSON
• Expected string key in object

AI-assisted analysis of karatelabs/karate@a22eb90246 (2026-09-12). Data as JSON: /api/errors/c76d1cc0bc3050e8. Report an issue: GitHub.

Appendix: source

Thrown at karate-js/src/main/java/io/karatelabs/js/JsonParser.java:300

                    pos++;
                }
                if (pos == fracStart) {
                    throw syntaxError("Invalid number: missing fraction digits");
                }
            }
            // exponent
            if (pos < len && (s.charAt(pos) == 'e' || s.charAt(pos) == 'E')) {
                isFloat = true;
                pos++;
                if (pos < len && (s.charAt(pos) == '+' || s.charAt(pos) == '-')) {
                    pos++;
                }
                int expStart = pos;
                while (pos < len && (s.charAt(pos) >= '0' && s.charAt(pos) <= '9')) {
                    pos++;
                }
                if (pos == expStart) {
                    throw syntaxError("Invalid number: missing exponent digits");
                }
            }
            String lit = s.substring(start, pos);
            if (isFloat) {
                return Double.parseDouble(lit);
            }
            // integer literal — narrow to Integer / Long / BigInteger to match
            // the json-smart contract (see JsonNumberContractTest).
            // Negative-zero integer form: json-smart returns Integer 0 (sign
            // lost). We match that to keep instanceof-Integer call sites in
            // karate-core stable (OAuth2Token.fromMap, W3cDriver, etc.).
            try {
                long v = Long.parseLong(lit);
                if (v >= Integer.MIN_VALUE && v <= Integer.MAX_VALUE) {
                    return (int) v;
                }
                return v;
            } catch (NumberFormatException nfe) {

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