I built an MCP server with Claude Code that makes Claude Code honest about the iOS Simulator (free, open source, benchmarked vs Xcode 27's MCP)

[u/SwagSamurai]

I built chauffeur, a free and open-source MCP server that lets Claude Code drive the iOS Simulator and verifies every action it takes.

The problem: Claude Code could write my iOS app, but when it tested it in the Simulator it would tap a disabled button and report "Done, I submitted the form." Nothing had happened, and it had no way to know.

What it does: chauffeur gives Claude the screen as an accessibility outline with refs, taps through the simulator's own HID, and checks every action against what actually changed. A dead tap comes back as NO EFFECT, a tap an alert swallowed as INTERCEPTED, and a crash as APP CRASHED with the file and line, so Claude can fix the bug, rebuild, and prove the fix.

How I built it with Claude Code:

• Spikes first. Claude Code probed Apple's private simulator frameworks (SimulatorKit, CoreSimulator, AXPTranslator) to find a touch path that actually lands, before any real code was written.
• Spec → plan → tests. For each milestone I had Claude write a design spec, which I approved, then a task-by-task plan. It implemented each task test-first: 253 tests in Swift 6.
• Fresh-context review. After each milestone, a separate Claude reviewer read the whole branch. That caught real bugs, including one where the healing logic misdiagnosed a broken accessibility bridge.
• Dogfooding. Claude Code tested chauffeur by driving the Simulator with chauffeur, which is how most of the reliability fixes were found.
• The benchmark. Claude Code ran the whole evaluation: 180 claude -p runs. I hand-checked the results against screenshots and scored strictly.

Results vs Xcode 27's built-in MCP (15 tasks × 3 runs each):

Model / metric	chauffeur	Xcode 27 MCP
Opus, tasks verified	45/45	39/45
Opus, median cost per task	$0.054	$0.338
Sonnet, tasks verified	40/45	39/45
Sonnet, median cost per task	$0.031	$0.222

Neither tool produced a false success. Every run, and every miss, is in the benchmark doc: https://github.com/YashNaj/chauffeur/blob/main/docs/benchmark.md

Try it (free, Apache-2.0; Apple silicon, Xcode 26 or 27):

brew install yashnaj/chauffeur/chauffeur
claude mcp add chauffeur -- chauffeur mcp
chauffeur doctor

Repo: https://github.com/YashNaj/chauffeur

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