karatelabs/karate · error · RuntimeException

param() needs two arguments

Error message

param() needs two arguments

What it means

HttpRequestBuilder exposes param() to scripts as a two-argument invokable (name, value) that adds a URL query parameter. Called with fewer than two arguments it throws this RuntimeException, failing fast instead of adding a malformed parameter.

Solutions

1. Pass both name and value: builder.param('page', '2')
2. Build params from a map using the map-accepting overload or loop with explicit key/value
3. Skip empty values in your loop instead of calling param() with them
4. For flag-style parameters, pass an empty-string value explicitly: param('verbose', '')

Example fix

// before
builder.param("page"); // throws
// after
builder.param("page", "2");

if (paramValue == null) throw new Error('query param ' + paramName + ' has no value');
builder.param(paramName, paramValue + '');

function paramArgsOk(name, value) { return name != null && value != null; }

When it happens

Trigger: Calling param() or param('page') with a single argument from a script; dynamic query-string construction where the value variable is undefined; confusing param(name, value) with param-getter methods elsewhere in the API.

Common situations: Building paginated/filtered requests where params come from a map or user input and some entries are missing; templated scripts where a placeholder failed to substitute; learners assuming param() with one arg sets a flag-style parameter.

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

• missing argument for multiPart()
• missing argument for file()
• missing argument for files()
• cache() requires (key, fn)
• header() needs two arguments

AI-assisted analysis of karatelabs/karate@a22eb90246 (2026-09-12). Data as JSON: /api/errors/fb11154db5a45445. Report an issue: GitHub.

Appendix: source

Thrown at karate-core/src/main/java/io/karatelabs/http/HttpRequestBuilder.java:730

            }
            return invoke();
        };
    }

    private JavaInvokable header() {
        return args -> {
            if (args.length < 2) {
                throw new RuntimeException("header() needs two arguments");
            }
            header(args[0] + "", args[1] + "");
            return this;
        };
    }

    private JavaInvokable param() {
        return args -> {
            if (args.length < 2) {
                throw new RuntimeException("param() needs two arguments");
            }
            param(args[0] + "", args[1] + "");
            return this;
        };
    }

    /**
     * The JS-facing plural forms of {@link #param} and {@link #header}. The Java
     * {@link #params(Map)} takes a {@code Map<String, List<String>>} and replaces what was
     * there, which is awkward to satisfy from JS - these accumulate and accept a scalar or a
     * list per key, matching the {@code params} and {@code headers} keywords.
     */
    private JavaInvokable params() {
        return args -> {
            if (args.length == 0 || !(args[0] instanceof Map<?, ?> map)) {
                throw new RuntimeException("params() needs a map argument");
            }
            map.forEach((k, v) -> {

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