SwiftFairy: an MCP server with zero LLM calls, giving coding agents deterministic Swift code review
hishnash · reddit · 2026-09-29
The developers shared SwiftFairy — a fully local MCP server that never calls a model, providing deterministic code review for Swift/SwiftUI coding agents:
- How it works: the agent passes changed files; the server parses them into a partial project graph (changed files + depended-on declarations), matches declarative rules, and returns line-attached findings with explanations and fixes. Another tool looks up API guidance before the agent starts.
- MCP design: serves both stdio (via a helper connecting to the Mac app over XPC, so all clients share one index) and loopback Streamable HTTP; supports current and previous protocol revisions; results are deduplicated and capped, with full guidance inlined only for small responses, otherwise identifiers for on-demand reads; unresolved dependencies return needscontext the agent answers in the background.
- Security: sandboxed, loopback-only, no network calls during review.
Works with Claude Code, Codex, Cursor and Gemini CLI. Paid Mac app, 24-hour free trial, needs Apple Silicon + macOS 26.
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