UI Testing Tools

Three UI-testing tools are registered by default and use CDP directly rather than a Bridge method. fb2k_evaluate is a fourth, conditional tool registered only when FB2K_ENABLE_EVAL is 1 or true.

fb2k_screenshot

Captures the WebView2 page and returns MCP image content containing base64 PNG data.

• Transport: Page.captureScreenshot (CDP)

Parameter	Type	Required	Description
fullPage	boolean	No	When true, temporarily sizes the viewport to the measured content before capture; omission captures the current viewport

Result: MCP image content with MIME type image/png.

Warm-up behavior

Every successful CDP connection attempts a best-effort 1×1 PNG capture before a real screenshot. Actual capture time depends on the host, page, and rendering state; no fixed latency is guaranteed.

fb2k_dom_snapshot

Gets a simplified DOM tree generated by evaluating a page-walking function.

• Parameters: none
• Transport: Runtime.evaluate (CDP)

Result format:

Each line contains tag#id.class "textContent"; indentation represents nesting. Text is included only for elements with a single text-node child and is truncated to 80 characters.

fb2k_evaluate

Executes a JavaScript expression in the WebView2 page.

• Registration: conditional on FB2K_ENABLE_EVAL=1 or FB2K_ENABLE_EVAL=true
• Transport: Runtime.evaluate (CDP)

Parameter	Type	Required	Description
expression	string	Yes	JavaScript expression to evaluate

Security boundary

This tool is disabled by default because it can run arbitrary JavaScript in the page. Enable it only for a trusted development or debugging session.

fb2k_console_messages

Gets up to the last 100 entries from window.__fb2kMcpConsoleLogs.

• Parameters: none
• Transport: Runtime.evaluate (CDP)

Example result:

[info] Page loaded [warn] Missing artwork for track 3 [error] Failed to connect to lyrics server