BrowserTools MCP

Instructions

Implementation Reference

• browser-tools-mcp/mcp-server.ts:251-299 (registration)

  MCP tool registration and handler for 'takeScreenshot'. Proxies the request via POST to the browser connector server's /capture-screenshot endpoint, handling discovery, errors, and response formatting.
  server.tool( "takeScreenshot", "Take a screenshot of the current browser tab", async () => { return await withServerConnection(async () => { try { const response = await fetch( `http://${discoveredHost}:${discoveredPort}/capture-screenshot`, { method: "POST", } ); const result = await response.json(); if (response.ok) { return { content: [ { type: "text", text: "Successfully saved screenshot", }, ], }; } else { return { content: [ { type: "text", text: `Error taking screenshot: ${result.error}`, }, ], }; } } catch (error: any) { const errorMessage = error instanceof Error ? error.message : String(error); return { content: [ { type: "text", text: `Failed to take screenshot: ${errorMessage}`, }, ], }; } }); } );
• browser-tools-server/browser-connector.ts:940-1249 (handler)

  Main handler for /capture-screenshot POST endpoint. Coordinates WebSocket communication with Chrome extension, receives screenshot dataURL, decodes/saves as PNG file, and handles macOS auto-paste into Cursor.
  async captureScreenshot(req: express.Request, res: express.Response) { console.log("Browser Connector: Starting captureScreenshot method"); console.log("Browser Connector: Request headers:", req.headers); console.log("Browser Connector: Request method:", req.method); if (!this.activeConnection) { console.log( "Browser Connector: No active WebSocket connection to Chrome extension" ); return res.status(503).json({ error: "Chrome extension not connected" }); } try { console.log("Browser Connector: Starting screenshot capture..."); const requestId = Date.now().toString(); console.log("Browser Connector: Generated requestId:", requestId); // Create promise that will resolve when we get the screenshot data const screenshotPromise = new Promise<{ data: string; path?: string; autoPaste?: boolean; }>((resolve, reject) => { console.log( `Browser Connector: Setting up screenshot callback for requestId: ${requestId}` ); // Store callback in map screenshotCallbacks.set(requestId, { resolve, reject }); console.log( "Browser Connector: Current callbacks:", Array.from(screenshotCallbacks.keys()) ); // Set timeout to clean up if we don't get a response setTimeout(() => { if (screenshotCallbacks.has(requestId)) { console.log( `Browser Connector: Screenshot capture timed out for requestId: ${requestId}` ); screenshotCallbacks.delete(requestId); reject( new Error( "Screenshot capture timed out - no response from Chrome extension" ) ); } }, 10000); }); // Send screenshot request to extension const message = JSON.stringify({ type: "take-screenshot", requestId: requestId, }); console.log( `Browser Connector: Sending WebSocket message to extension:`, message ); this.activeConnection.send(message); // Wait for screenshot data console.log("Browser Connector: Waiting for screenshot data..."); const { data: base64Data, path: customPath, autoPaste, } = await screenshotPromise; console.log("Browser Connector: Received screenshot data, saving..."); console.log("Browser Connector: Custom path from extension:", customPath); console.log("Browser Connector: Auto-paste setting:", autoPaste); // Always prioritize the path from the Chrome extension let targetPath = customPath; // If no path provided by extension, fall back to defaults if (!targetPath) { targetPath = currentSettings.screenshotPath || getDefaultDownloadsFolder(); } // Convert the path for the current platform targetPath = convertPathForCurrentPlatform(targetPath); console.log(`Browser Connector: Using path: ${targetPath}`); if (!base64Data) { throw new Error("No screenshot data received from Chrome extension"); } try { fs.mkdirSync(targetPath, { recursive: true }); console.log(`Browser Connector: Created directory: ${targetPath}`); } catch (err) { console.error( `Browser Connector: Error creating directory: ${targetPath}`, err ); throw new Error( `Failed to create screenshot directory: ${ err instanceof Error ? err.message : String(err) }` ); } const timestamp = new Date().toISOString().replace(/[:.]/g, "-"); const filename = `screenshot-${timestamp}.png`; const fullPath = path.join(targetPath, filename); console.log(`Browser Connector: Full screenshot path: ${fullPath}`); // Remove the data:image/png;base64, prefix if present const cleanBase64 = base64Data.replace(/^data:image\/png;base64,/, ""); // Save the file try { fs.writeFileSync(fullPath, cleanBase64, "base64"); console.log(`Browser Connector: Screenshot saved to: ${fullPath}`); } catch (err) { console.error( `Browser Connector: Error saving screenshot to: ${fullPath}`, err ); throw new Error( `Failed to save screenshot: ${ err instanceof Error ? err.message : String(err) }` ); } // Check if running on macOS before executing AppleScript if (os.platform() === "darwin" && autoPaste === true) { console.log( "Browser Connector: Running on macOS with auto-paste enabled, executing AppleScript to paste into Cursor" ); // Create the AppleScript to copy the image to clipboard and paste into Cursor // This version is more robust and includes debugging const appleScript = ` -- Set path to the screenshot set imagePath to "${fullPath}" -- Copy the image to clipboard try set the clipboard to (read (POSIX file imagePath) as «class PNGf») on error errMsg log "Error copying image to clipboard: " & errMsg return "Failed to copy image to clipboard: " & errMsg end try -- Activate Cursor application try tell application "Cursor" activate end tell on error errMsg log "Error activating Cursor: " & errMsg return "Failed to activate Cursor: " & errMsg end try -- Wait for the application to fully activate delay 3 -- Try to interact with Cursor try tell application "System Events" tell process "Cursor" -- Get the frontmost window if (count of windows) is 0 then return "No windows found in Cursor" end if set cursorWindow to window 1 -- Try Method 1: Look for elements of class "Text Area" set foundElements to {} -- Try different selectors to find the text input area try -- Try with class set textAreas to UI elements of cursorWindow whose class is "Text Area" if (count of textAreas) > 0 then set foundElements to textAreas end if end try if (count of foundElements) is 0 then try -- Try with AXTextField role set textFields to UI elements of cursorWindow whose role is "AXTextField" if (count of textFields) > 0 then set foundElements to textFields end if end try end if if (count of foundElements) is 0 then try -- Try with AXTextArea role in nested elements set allElements to UI elements of cursorWindow repeat with anElement in allElements try set childElements to UI elements of anElement repeat with aChild in childElements try if role of aChild is "AXTextArea" or role of aChild is "AXTextField" then set end of foundElements to aChild end if end try end repeat end try end repeat end try end if -- If no elements found with specific attributes, try a broader approach if (count of foundElements) is 0 then -- Just try to use the Command+V shortcut on the active window -- This assumes Cursor already has focus on the right element keystroke "v" using command down delay 1 keystroke "here is the screenshot" delay 1 -- Try multiple methods to press Enter key code 36 -- Use key code for Return key delay 0.5 keystroke return -- Use keystroke return as alternative return "Used fallback method: Command+V on active window" else -- We found a potential text input element set inputElement to item 1 of foundElements -- Try to focus and paste try set focused of inputElement to true delay 0.5 -- Paste the image keystroke "v" using command down delay 1 -- Type the text keystroke "here is the screenshot" delay 1 -- Try multiple methods to press Enter key code 36 -- Use key code for Return key delay 0.5 keystroke return -- Use keystroke return as alternative return "Successfully pasted screenshot into Cursor text element" on error errMsg log "Error interacting with found element: " & errMsg -- Fallback to just sending the key commands keystroke "v" using command down delay 1 keystroke "here is the screenshot" delay 1 -- Try multiple methods to press Enter key code 36 -- Use key code for Return key delay 0.5 keystroke return -- Use keystroke return as alternative return "Used fallback after element focus error: " & errMsg end try end if end tell end tell on error errMsg log "Error in System Events block: " & errMsg return "Failed in System Events: " & errMsg end try `; // Execute the AppleScript exec(`osascript -e '${appleScript}'`, (error, stdout, stderr) => { if (error) { console.error( `Browser Connector: Error executing AppleScript: ${error.message}` ); console.error(`Browser Connector: stderr: ${stderr}`); // Don't fail the response; log the error and proceed } else { console.log(`Browser Connector: AppleScript executed successfully`); console.log(`Browser Connector: stdout: ${stdout}`); } }); } else { if (os.platform() === "darwin" && !autoPaste) { console.log( `Browser Connector: Running on macOS but auto-paste is disabled, skipping AppleScript execution` ); } else { console.log( `Browser Connector: Not running on macOS, skipping AppleScript execution` ); } } res.json({ path: fullPath, filename: filename, }); } catch (error) { const errorMessage = error instanceof Error ? error.message : String(error); console.error( "Browser Connector: Error capturing screenshot:", errorMessage ); res.status(500).json({ error: errorMessage, }); } }
• chrome-extension/devtools.js:967-1005 (handler)

  Chrome extension WebSocket message handler for 'take-screenshot'. Uses chrome.tabs.captureVisibleTab to capture visible tab as PNG dataURL and sends back via WebSocket with path and autoPaste settings.
  } else if (message.type === "take-screenshot") { console.log("Chrome Extension: Taking screenshot..."); // Capture screenshot of the current tab chrome.tabs.captureVisibleTab(null, { format: "png" }, (dataUrl) => { if (chrome.runtime.lastError) { console.error( "Chrome Extension: Screenshot capture failed:", chrome.runtime.lastError ); ws.send( JSON.stringify({ type: "screenshot-error", error: chrome.runtime.lastError.message, requestId: message.requestId, }) ); return; } console.log("Chrome Extension: Screenshot captured successfully"); // Just send the screenshot data, let the server handle paths const response = { type: "screenshot-data", data: dataUrl, requestId: message.requestId, // Only include path if it's configured in settings ...(settings.screenshotPath && { path: settings.screenshotPath }), // Include auto-paste setting autoPaste: settings.allowAutoPaste, }; console.log("Chrome Extension: Sending screenshot data response", { ...response, data: "[base64 data]", }); ws.send(JSON.stringify(response)); }); } else if (message.type === "get-current-url") {
• browser-tools-server/browser-connector.ts:620-632 (registration)

  Express route registration for POST /capture-screenshot endpoint, which delegates to the captureScreenshot handler method.
  this.app.post( "/capture-screenshot", async (req: express.Request, res: express.Response) => { console.log( "Browser Connector: Received request to /capture-screenshot endpoint" ); console.log("Browser Connector: Request body:", req.body); console.log( "Browser Connector: Active WebSocket connection:", !!this.activeConnection ); await this.captureScreenshot(req, res); }