What causes "Expected ',' or ']' in array" in karatelabs/karate?

Go to the reported position and insert the missing ',' between array elements.

Expected ',' or ']' in array

Error message

Expected ',' or ']' in array

What it means

Thrown by JsonParser.parseArray when the character following a complete array element is neither ',' (next element) nor ']' (end of array). The array contains a malformed separator or stray token where the grammar only allows ',' or ']'.

Solutions

Go to the reported position and insert the missing ',' between array elements.
Remove the stray character that is not ',' or ']'.
Replace semicolons or other separators with commas.
Generate arrays programmatically with a JSON serializer rather than by hand.

Example fix

// before
'[1, 2 3]'
// after
'[1, 2, 3]'

Defensive patterns

Strategy: validation

Validate before calling

// Pre-validate array element separators with a standard parser
try {
    new com.fasterxml.jackson.databind.ObjectMapper().readTree(json);
} catch (JsonProcessingException e) {
    throw new IllegalArgumentException("Invalid array separator: " + e.getOriginalMessage());
}

Type guard

static boolean hasBalancedArraySyntax(String s) {
    return s != null && s.trim().matches("\\[.*\\]");
} // combine with a real parse for full safety

Try / catch

try {
    Object list = Json.parse(raw);
} catch (JsonSyntaxException e) {
    throw new IllegalArgumentException("Malformed JSON array near: " + e.getMessage());
}

Prevention

Use commas, never semicolons or spaces, between array elements.
Format JSON in an editor that flags syntax errors while typing.
Serialize arrays from code rather than writing them by hand.
Validate user-pasted JSON with JSON.parse/linter before accepting it.

When it happens

Trigger: Parsing input like '[1 2]' (missing comma between elements), '[1; 2]', or '[1 }]' — an unexpected character appears between elements.

Common situations: Hand-written arrays missing commas, pasting values from other languages (e.g. semicolon-separated), naive string building of arrays, editing generated fixtures by hand.

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

AI-assisted analysis of karatelabs/karate@a22eb90246 (2026-09-12). Data as JSON: /api/errors/7f162d00761aa91e. Report an issue: GitHub.

Appendix: source

Thrown at karate-js/src/main/java/io/karatelabs/js/JsonParser.java:174

            while (true) {
                skipWs();
                list.add(parseValue());
                skipWs();
                if (pos >= len) {
                    throw syntaxError("Unexpected end of JSON input in array");
                }
                char c = s.charAt(pos);
                if (c == ',') {
                    pos++;
                    // trailing-comma rejected: the next parseValue() lands on
                    // ']' and parseValue's default branch throws.
                    continue;
                }
                if (c == ']') {
                    pos++;
                    return list;
                }
                throw syntaxError("Expected ',' or ']' in array");
            }
        }

        private String parseString() {
            // we know s.charAt(pos) == '"'
            pos++;
            StringBuilder sb = new StringBuilder();
            while (pos < len) {
                char c = s.charAt(pos);
                if (c == '"') {
                    pos++;
                    return sb.toString();
                }
                if (c == '\\') {
                    pos++;
                    if (pos >= len) {
                        throw syntaxError("Unexpected end of JSON input in string escape");
                    }

View on GitHub (pinned to a22eb90246)