karatelabs/karate · error · UnsupportedOperationException

PDF generation not supported on WebDriver backend

Error message

PDF generation not supported on WebDriver backend

What it means

W3cDriver.pdf() unconditionally throws UnsupportedOperationException because PDF generation is a Chrome DevTools (Page.printToPDF) capability that the plain WebDriver protocol does not provide. It is a static capability declaration, not a runtime condition.

Solutions

1. Switch the driver type to chrome/cdp (DevTools-backed) in the karate config to get PDF support
2. Avoid calling pdf() in tests that must run on the W3C backend, or guard with a capability check
3. Generate the PDF out-of-band (e.g. headless Chrome CLI, server-side library) if WebDriver must stay

Example fix

// before (karate-config)
{ type: 'chromedriver' }  // W3C backend
// after
{ type: 'chrome' }  // CDP backend, supports pdf()

// guard before calling
if (!"chrome".equals(driverType)) {
    skipPdfScenario();
}

boolean supportsPdf(String driverType) { return "chrome".equals(driverType); }

try {
    byte[] pdf = karate.pdf("/path/out.pdf");
} catch (UnsupportedOperationException e) {
    // W3C backend: generate via headless chrome CLI instead
}

When it happens

Trigger: Calling driver.pdf(...) (or the Karate pdf API) while running on the W3C WebDriver backend instead of the CDP driver.

Common situations: Test suite written against chrome/cdp driver later run with a generic WebDriver; switching driver 'type' in config between runs; porting CDP-specific scripts to a grid/selenium setup.

Understand the failure class

Background: UnsupportedOperationException and "is not supported" errors: when a library deliberately refuses a call — this error's family across 30 libraries.

Related errors

• Request interception not supported on WebDriver backend
• Dialog callback handler not supported on WebDriver backend…
• karate.match(String) is not available in this context
• karate.call() is not available in this context
• inputFile not supported by this driver

AI-assisted analysis of karatelabs/karate@a22eb90246 (2026-09-12). Data as JSON: /api/errors/894ab9b012ab713f. Report an issue: GitHub.

Appendix: source

Thrown at karate-core/src/main/java/io/karatelabs/driver/w3c/W3cDriver.java:302

            session.sendAlertText(input);
        }
        if (accept) {
            session.acceptAlert();
        } else {
            session.dismissAlert();
        }
    }

    // ========== CoreDriver Tier 2: Extended Primitives ==========

    @Override
    public Mouse mouse() {
        return new W3cMouse(session);
    }

    @Override
    public byte[] pdf(Map<String, Object> pdfOptions) {
        throw new UnsupportedOperationException(
                "PDF generation not supported on WebDriver backend");
    }

    @Override
    public Map<String, Object> cookie(String name) {
        return session.getCookie(name);
    }

    @Override
    public void cookie(Map<String, Object> cookie) {
        session.addCookie(cookie);
    }

    @Override
    public void intercept(List<String> patterns, InterceptHandler handler) {
        throw new UnsupportedOperationException(
                "Request interception not supported on WebDriver backend");
    }

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