karatelabs/karate · error · RuntimeException

driver keyword requires a URL argument

Error message

driver keyword requires a URL argument

What it means

The standalone `driver` keyword sets the browser driver's URL and requires the step text to be a non-empty expression evaluating to the server URL. When the text is null or blank there is nothing to evaluate or navigate to, so the executor throws immediately before evaluation.

Solutions

1. Provide a URL: `driver 'http://localhost:9222'` or `driver myUrlVariable`
2. If configuring instead of navigating, use `configure driver = {...}`
3. Ensure the URL expression is on the same step text, not a docstring
4. print the URL variable to confirm it is populated

Example fix

// before
* driver
// after
* driver 'http://localhost:9222'

* if (!driverUrl) karate.fail('driver step needs a URL')

When it happens

Trigger: A `driver` step with no text (e.g. `* driver` alone); text consisting only of whitespace; a step parsed such that the URL ended up in a docstring or argument instead of the text.

Common situations: Deleting the URL during refactoring; template placeholders like `driver <url>` left unfilled; formatting errors where the URL landed on a following line treated as a separate step.

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

• driver URL evaluated to null:
• element not found:
• missing array argument 'patterns':
• missing 'mock' or 'handler' in intercept config
• unknown window operation

AI-assisted analysis of karatelabs/karate@a22eb90246 (2026-09-12). Data as JSON: /api/errors/302f784f351f1e9d. Report an issue: GitHub.

Appendix: source

Thrown at karate-core/src/main/java/io/karatelabs/core/StepExecutor.java:3082

        // Bare variable / JS expression: return the live object so mutations made
        // after the configure step are reflected. Any embedded #(...) it carries is
        // left intact and resolved per-request on a fresh copy.
        return runtime.eval(wrapJsonLikeExpression(expr));
    }

    // ========== Browser Driver ==========

    /**
     * Execute the driver keyword - navigate to a URL.
     * Examples:
     * - driver 'http://localhost:8080'
     * - driver serverUrl + '/path'
     * - driver myUrl
     */
    private void executeDriver(Step step) {
        String text = step.getText();
        if (text == null || text.trim().isEmpty()) {
            throw new RuntimeException("driver keyword requires a URL argument");
        }

        // Evaluate the expression to get the URL
        Object result = runtime.eval(text.trim());
        if (result == null) {
            throw new RuntimeException("driver URL evaluated to null: " + text);
        }

        String url = result.toString();

        // Get the driver (initializes lazily if needed)
        io.karatelabs.driver.Driver driver = runtime.getDriver();

        // Navigate to the URL
        driver.setUrl(url);
    }

    // ========== Karate Expression Helpers ==========

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