fix(agents): use cmd /c npx on Windows for init-agents MCP config by SeoJaeWan · Pull Request #39221 · microsoft/playwright

SeoJaeWan · 2026-02-11T10:32:33Z

Summary

On Windows, npx resolves to npx.cmd (a batch file) which cannot be executed by MCP clients using child_process.spawn() without shell: true
Added platform detection in generateAgents.ts for Claude generator to use cmd /c npx on Windows
Other generators unchanged: VS Code handles .cmd resolution internally, Copilot runs on GitHub cloud, Opencode spawns a shell

Changes

ClaudeGenerator.init(): generates .mcp.json with cmd /c npx on Windows
Added 1 test in tests/mcp/init-agents.spec.ts verifying MCP config output for claude generator

Test plan

Build passes
All 4 init-agents tests pass
Verified VS Code works with plain npx on Windows (no cmd /c needed)
Test uses if/else platform branching, validated across CI environments (ubuntu, macos, windows)

SeoJaeWan · 2026-02-11T10:36:50Z

@microsoft-github-policy-service agree

Skn0tt · 2026-02-11T12:59:22Z

Instead of a docs note, i'd prefer fixing our output - would you like to contribute a PR that fixes the install command?

SeoJaeWan · 2026-02-11T14:11:03Z

@Skn0tt Updated the PR to fix the init-agents output instead of adding a docs note.

Changes:

Added npxCommand() helper in generateAgents.ts to wrap npx with cmd /c on Windows
Applied to Claude, VSCode, and Opencode generators (local execution)
Left Copilot generator unchanged since it runs remotely on GitHub (Linux) via remote: true

Verified the generated configs on Windows for all 4 generators.

Skn0tt · 2026-02-11T14:22:00Z

Thanks! Could you add tests to tests/mcp/init-agents.spec.ts?

SeoJaeWan · 2026-02-11T14:27:32Z

@Skn0tt Thanks for the review! Added tests in tests/mcp/init-agents.spec.ts that verify the generated MCP config for each generator (claude, vscode, opencode). The tests assert platform-correct command/args values using process.platform, so they will validate across all 3 CI environments (ubuntu, macos, windows).

Skn0tt

we're getting there! it seems that not all targets have the distinction (copilot, opencode), so let's keep this change focused on those that do.

Skn0tt · 2026-02-11T14:37:23Z

packages/playwright/src/agents/generateAgents.ts

        asOpencodeTool(tools, tool);
    }

+    const { command, args } = npxCommand(['playwright', 'run-test-mcp-server']);


opencode seems to spawn a shell, so we should also pick 'npx' here. maybe let's not use the abstraction?

Skn0tt · 2026-02-11T14:42:26Z

tests/mcp/init-agents.spec.ts

+  await runInitAgents({ cwd: baseDir, args: ['--loop', 'claude'] });
+
+  const mcpJson = JSON.parse(fs.readFileSync(path.join(baseDir, '.mcp.json'), 'utf-8'));
+  expect(mcpJson.mcpServers['playwright-test'].command).toBe(expectedCommand);


we usually have this structure in our test suite so that tests can be copied easily, let's match that.

Suggested change

expect(mcpJson.mcpServers['playwright-test'].command).toBe(expectedCommand);

if (process.platform === 'win32')

expect(mcpJson.mcpServers['playwright-test'].command).toBe(expectedCommand);

else

expect(mcpJson.mcpServers['playwright-test'].command).toBe(expectedCommand);

SeoJaeWan · 2026-02-11T15:02:01Z

@Skn0tt Thank you so much for the thorough review. Sorry for the over-engineering — I didn’t realize opencode spawns a shell, so the cmd /c wrapping isn’t needed there.

I’ve narrowed the scope to only the Claude and VSCode generators, removed the npxCommand() abstraction, reverted the Copilot and Opencode changes, and restructured the tests using the suggested if/else pattern.

Appreciate the guidance — I’ve updated the PR with these changes.

Skn0tt · 2026-02-11T15:15:18Z

Cool, i'll quickly test this out myself on Windows. Could you do me a favor and revert those whitespace changes in the md file?

SeoJaeWan · 2026-02-11T15:20:09Z

@Skn0tt Done! Reverted the whitespace change in the md file.

Skn0tt · 2026-02-11T15:35:35Z

I could repro the bug with Claude and can see the fix works. But with VS Code, it already worked prior to the fix. Did you see this happen under VS Code as well? If not, let's trim down this PR to just the Claude fix.

Taking a step back, I wonder if this should be fixed by Claude Code itself - if what we generate is platform-specific, it can't be comitted into repositories that need to work under different platforms.

SeoJaeWan · 2026-02-11T15:38:10Z

@Skn0tt Thanks for checking! Sorry for the noise — you’re right.

I was able to reproduce the issue with Claude Code, but I haven’t been able to reproduce it in VS Code either (it seems to work there even before this change). I had already started trimming the PR, and I’ll update it to keep the fix scoped to the Claude generator only.

Skn0tt · 2026-02-11T15:39:54Z

I have a weird question to ask. Are you a human? You respond so quickly and so well-written that nowadays, I have to suspect you're OpenClaw!

SeoJaeWan · 2026-02-11T15:41:36Z

I’m a Korean developer, and I’m genuinely excited that I can contribute to open source for the first time.

It’s 12:40 AM here in Korea, and I can’t fall asleep because I’m so focused on this PR. I’m just staying up and waiting for the review updates.

SeoJaeWan · 2026-02-11T15:42:10Z

I’m sorry for the mistakes — my enthusiasm got ahead of me.

SeoJaeWan · 2026-02-11T15:42:31Z

@Skn0tt Updated — narrowed the scope to Claude generator only. VS Code confirmed working with plain npx on Windows. The PR now has just the Claude fix + 1 test.

SeoJaeWan · 2026-02-11T15:44:52Z

@Skn0tt Your suspicion is understandable, and I realize I’ve made too many mistakes. I sincerely apologize for that.

Skn0tt

looks good to me. i'm torn on whether we should be fixing it, since it's really on claude to do it - but erring on the side of making it work today, so that we can revert once claude fixed it. cc @dgozman for double-checking.

Skn0tt · 2026-02-11T15:47:15Z

Your suspicion is understandable, and I realize I’ve made too many mistakes. I sincerely apologize for that.

No worries! It's not the mistakes, it's the speed that got me suspicious :D Good to hear you're enjoying contributing to open source, it's a wonderful thing 👍

SeoJaeWan · 2026-02-11T15:49:46Z

@Skn0tt
Thank you so much for being so kind about it — I really appreciate it.

It’s getting late here, so I think I should finally get some sleep. I’ll be able to respond again in about 5 hours.

This PR has been one of the most nerve-wracking, thrilling, and exciting moments in my developer life — and I’m grateful for your patience and encouragement. Thank you!

github-actions · 2026-02-11T16:24:39Z

Test results for "tests 1"

5 failed
❌ [playwright-test] › aria-snapshot-file.spec.ts:225 › should respect config.expect.toMatchAriaSnapshot.pathTemplate @macos-latest-node20
❌ [playwright-test] › playwright.spec.ts:485 › should work with video: on-first-retry @macos-latest-node20
❌ [playwright-test] › playwright.trace.spec.ts:137 › should not throw with trace: on-first-retry and two retries in the same worker @macos-latest-node20
❌ [playwright-test] › reporter.spec.ts:251 › created › should not have internal error when steps are finished after timeout @macos-latest-node20
❌ [playwright-test] › update-aria-snapshot.spec.ts:669 › update-source-method › should overwrite source when specified in the config @macos-latest-node20

1 flaky

⚠️ [playwright-test] › ui-mode-trace.spec.ts:700 › should indicate current test status `@macos-latest-node20`

38553 passed, 843 skipped

Merge workflow run.

github-actions · 2026-02-11T17:13:15Z

Test results for "MCP"

5 failed
❌ [chromium] › mcp/cli-save-as.spec.ts:19 › screenshot @mcp-macos-15
❌ [chromium] › mcp/http.spec.ts:263 › http transport shared context @mcp-macos-15
❌ [chromium] › mcp/launch.spec.ts:21 › test reopen browser @mcp-macos-15
❌ [firefox] › mcp/cli-session.spec.ts:50 › close non-running session @mcp-macos-15
❌ [firefox] › mcp/cli-session.spec.ts:152 › workspace isolation - sessions in different workspaces are isolated @mcp-macos-15

4787 passed, 135 skipped

Merge workflow run.

fix(agents): use cmd /c npx on Windows for init-agents MCP config

9cbfb37

SeoJaeWan force-pushed the docs/agents-windows-mcp-workaround branch from 58e7f6c to 9cbfb37 Compare February 11, 2026 14:06

SeoJaeWan changed the title ~~docs(agents): add Windows workaround for MCP server npx command~~ fix(agents): use cmd /c npx on Windows for init-agents MCP config Feb 11, 2026

test(agents): add mcp config tests for init-agents

6b7c3e6

Skn0tt reviewed Feb 11, 2026

View reviewed changes

fix(agents): use cmd /c npx on Windows for init-agents MCP config

70c8001

chore: revert whitespace change in test-agents-js.md

3e01a7c

fix(agents): use cmd /c npx on Windows for init-agents MCP config

eb3044a

Skn0tt approved these changes Feb 11, 2026

View reviewed changes

Skn0tt requested a review from dgozman February 11, 2026 15:45

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Test results for "tests 1"

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Test results for "MCP"

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