karatelabs/karate · error · RuntimeException

pretty() needs one argument

Error message

pretty() needs one argument

What it means

pretty() is a Karate JS utility that pretty-prints a value: Maps/Lists via JSON formatting, XML Nodes via Xml.toString. It throws this error when called with zero arguments, since there is no value to format.

Solutions

1. Pass the value to print: pretty(myMap), pretty(response), or pretty(xmlNode).
2. If the value may be undefined, print a fallback string instead: pretty(variable || '(missing)').
3. For plain XML strings prefer prettyXml(), which also accepts strings.

Example fix

// before
print pretty()
// after
print pretty(response)

if (response) { print pretty(response) } else { print '(no response)' }

When it happens

Trigger: karate.pretty() with no arguments, e.g. pretty() instead of pretty(response).

Common situations: Debug-printing in a Scenario and forgetting to pass the variable; the variable name was deleted during cleanup; copying karate.pretty from docs without adapting the argument.

Understand the failure class

Background: "missing required argument" and "the following required arguments were not provided": what required-argument errors mean and how to fix them — this error's family across 20 libraries.

Related errors

• eval() needs one argument
• expect() needs at least one argument
• append() needs at least two arguments
• appendTo() needs at least two arguments: list and item(s)
• extract() needs three arguments: text, regex, group

AI-assisted analysis of karatelabs/karate@a22eb90246 (2026-09-12). Data as JSON: /api/errors/e9bbf30f3b05fa98. Report an issue: GitHub.

Appendix: source

Thrown at karate-core/src/main/java/io/karatelabs/core/KarateJsUtils.java:392

    static JavaInvokable pause() {
        return args -> {
            if (args.length == 0 || args[0] == null) {
                return null;
            }
            long millis = ((Number) args[0]).longValue();
            try {
                Thread.sleep(millis);
            } catch (InterruptedException e) {
                Thread.currentThread().interrupt();
            }
            return null;
        };
    }

    static JavaInvokable pretty() {
        return args -> {
            if (args.length == 0) {
                throw new RuntimeException("pretty() needs one argument");
            }
            Object obj = args[0];
            if (obj instanceof Map || obj instanceof List) {
                return StringUtils.formatJson(obj);
            } else if (obj instanceof Node) {
                return Xml.toString((Node) obj, true);
            } else {
                return obj != null ? obj.toString() : "null";
            }
        };
    }

    /**
     * Generate a range of integers.
     * Usage: karate.range(0, 5) => [0, 1, 2, 3, 4]
     *        karate.range(0, 10, 2) => [0, 2, 4, 6, 8]
     *        karate.range(5, 0, -1) => [5, 4, 3, 2, 1]
     */

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