karatelabs/karate · error · RuntimeException

invalid json: not a JSON object or array

Error message

invalid json: not a JSON object or array

What it means

After parsing, parseLenient() checks that the result is a JSON object or array; scalars like `123`, `"text"`, `true`, or `null` are rejected with this RuntimeException. Karate's Json document model only supports Map/List roots.

Solutions

1. Wrap the scalar in an object or array, e.g. "{\"value\": 123}"
2. Use a plain JSON parser (JSONValue.parse) if scalars are legitimate for your use case
3. Check that the file/endpoint actually returns JSON documents, not text

Example fix

// before
Json json = Json.of("42");
// after
Json json = Json.of("{\"value\": 42}");

String t = json == null ? null : json.trim();
boolean looksLikeDocument = t != null && (t.startsWith("{") || t.startsWith("["));

try { Object o = Json.parseLenient(s); } catch (RuntimeException e) { if (e.getMessage().contains("not a JSON object or array")) { o = Map.of("value", JSONValue.parse(s)); } else { throw e; } }

When it happens

Trigger: Json.parseLenient("hello world"), Json.parseLenient("123"), Json.of("null"), or Json.of("\"a string\"") — input parses but is not an object/array.

Common situations: Feeding log lines, plain text, or scalar values (numbers, quoted strings) where a JSON document was expected.

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

• invalid json: input is null or blank
• invalid json
• input must not be null
• input string must not be empty or blank
• cannot replace root path $

AI-assisted analysis of karatelabs/karate@a22eb90246 (2026-09-12). Data as JSON: /api/errors/4271daaa51957d1f. Report an issue: GitHub.

Appendix: source

Thrown at karate-core/src/main/java/io/karatelabs/common/Json.java:128

                throw new IllegalArgumentException("input string must not be empty or blank");
            }
            return new Json(JsonPath.parse(parseLenient(s)));
        } else if (any instanceof List || any instanceof Map) {
            return new Json(JsonPath.parse(any));
        } else {
            String json = JSONValue.toJSONString(any);
            return new Json(JsonPath.parse(json));
        }
    }

    public static Object parseLenient(String json) {
        if (json == null || json.isBlank()) {
            throw new RuntimeException("invalid json: input is null or blank");
        }
        try {
            Object result = JSONValue.parseKeepingOrder(json);
            if (!isMapOrList(result)) {
                throw new RuntimeException("invalid json: not a JSON object or array");
            }
            return result;
        } catch (RuntimeException e) {
            throw e;
        } catch (Exception e) {
            throw new RuntimeException("invalid json: " + e.getMessage(), e);
        }
    }

    public static boolean isMapOrList(Object o) {
        return o instanceof Map || o instanceof List;
    }

    public static Object parseStrict(String json) {
        return parseStrict(json, false);
    }

    public static Object parseStrict(String json, boolean keepOrder) {

View on GitHub (pinned to a22eb90246)