Automate debugging with the Playwright MCP server

Key Concepts:

• Playwright MCP Server: A tool that allows Copilot agent mode to interact with a web application, understand bugs, and verify fixes.
• Copilot Agent Mode: An AI assistant that can analyze code, identify issues, and propose solutions.
• To-Do MCP Server: A server (currently in preview) used by Copilot to track its work and progress.
• Playwright: A framework for end-to-end testing and automation of web applications.
• Selectors: CSS or XPath expressions used to identify elements on a web page.
• Svelte Component: A reusable UI component built using the Svelte JavaScript framework.
• Network Calls: HTTP requests made by a web application to a server.
• Front-end: The client-side code of a web application (e.g., HTML, CSS, JavaScript).
• Back-end: The server-side code of a web application (e.g., APIs, databases).

Bug Reproduction and Analysis with Playwright MCP Server

The Playwright MCP server facilitates bug identification and resolution by enabling Copilot agent mode to directly interact with a web application. The process begins with a user reporting a bug and providing reproduction steps.

• Initial Bug Report: The user describes the bug and provides steps to reproduce it.
• Copilot Task Tracking: Copilot uses the to-do MCP server (in preview) to manage the task of investigating and fixing the bug.
• Playwright Interaction: Copilot utilizes Playwright to execute the provided reproduction steps. It starts the server and uses Playwright to perform the steps to confirm the bug.
• Page Analysis: Copilot uses Playwright to inspect the web page's current state, understanding the existing elements and their behavior. The example uses a call to the page in Playwright to get an understanding of what's currently there.
• Bug Reproduction Attempt: Copilot attempts to reproduce the bug using Playwright, specifically interacting with the relevant elements (e.g., a filter using the publisher selector).
• Bug Confirmation: Copilot confirms the bug exists as reported, observing the incorrect behavior (e.g., the filter not working). In the example, it discovers things are exactly as reported - the filter doesn't do anything.

Code Analysis and Fix Implementation

After confirming the bug, Copilot analyzes the application code to identify the root cause.

• Front-End Inspection: Copilot examines the front-end code, such as a Svelte component (e.g., games_list Svelte component), to check for any logical errors. In the example, it determines the code there looks good.
• Network Call Verification: Copilot uses Playwright to monitor the network calls made by the application, ensuring data is being requested and received correctly.
• Back-End Analysis: Copilot investigates the back-end code, where the root cause of the bug is ultimately found. In the example, it opens the back-end and discovers a typo.
• Fix Generation: Copilot generates a fix for the identified bug.
• Fix Implementation: The generated fix is applied to the code.

Fix Verification and Task Completion

After implementing the fix, Copilot verifies its effectiveness using Playwright.

• Playwright Verification: Copilot uses Playwright to re-execute the reproduction steps and confirm the bug is resolved. It waits for the page to refresh, then tries the selector again.
• Bug Resolution Confirmation: Copilot confirms the bug is no longer present and the application behaves as expected. In the example, everything is working fine now.
• Task Completion: Copilot updates the to-do list to mark the task as successfully completed. One last update to the to-do list to mark that we've successfully completed the task.

Conclusion

The Playwright MCP server, in conjunction with Copilot agent mode, provides a powerful workflow for debugging and fixing web applications. It enables Copilot to understand bugs, analyze code, and verify fixes in a live environment, extending its capabilities beyond end-to-end testing to include live validation of changes. With the help of the Playwright MCP server we can allow Copilot to better support us as we're creating web applications, not solely creating end-to-end tests, but also doing live validation of our changes.