Marvin – Open-source macOS AI coding IDE that learns from its own sessions Robert Ilisei released MARVIN, an open-source macOS AI coding IDE that uses a single assistant with enforced phases and a knowledge graph to reduce first-message context from 566K to ~13.4K tokens, cutting token costs to about 1/27th. The app, currently at v0.1.104, runs locally with a bundled sidecar and requires Anthropic credentials, available via Homebrew as 'marvin-ai'. M oderately A dvanced R obotic V irtual I ntelligence N etwork. A pair-programming AI assistant. You drive vision and business decisions. MARVIN drives architecture, infrastructure, code, tests, docs, and security. You say "let's build the login page" — MARVIN dives in: reads the codebase, proposes the schema + wiring + tests, executes with explicit confirms, commits. "Here I am, brain the size of a planet, and they ask me to build a login page." — MARVIN, probably A real session on MARVIN's own repo, unedited: two graph queries before the first file read, an answer with file and line citations, 19 seconds. One assistant, enforced discipline — a design for AI pair-programming that survives real projects Why AI coding assistance decays on real projects, and the four bets MARVIN makes against the current grain: One assistant with enforced phases— not an agent team; subagents are structurally unable to writeThe knowledge graph before the file read— structural answers at ~1/27th the token cost measured on this repo , with file:line citationsDeterministic contracts at the tool gate— enforced, not politely requested in the promptLocal-first, no backend— inference straight to Anthropic; credentials never leave your machineWith measured results first-message context: 566K → ~13.4K tokens , five architecture diagrams, and anonymized transcripts from real production sessions. The exhaustive companion — every subsystem down to the code — is the Technical Reference . Both are also available as PDFs: white paper · technical reference . MARVIN has two components that work together: | Component | Location | Role | |---|---|---| macOS app | macos/ | Native SwiftUI app — IDE shell, chat, file tree, source control, terminal, diff viewer | Sidecar | sidecar/ | Next.js 16 server on :3030 — Claude Agent SDK runner, tool policy, git API, file API, session storage | The Swift app talks to the sidecar over localhost:3030 . In a brew install the sidecar is bundled inside MARVIN.app/Contents/Resources/ alongside a pinned Node 22 runtime and spawned by the SwiftUI process on launch; quitting MARVIN cleans it up. See ADR-0023 /RobertIlisei/MARVIN/blob/main/docs/decisions/0023-brew-distributable-bundled-sidecar.md . Releases.Homebrew installs the latest tagged release currentlyv0.1.104 . main and development are fast-forwarded together at each release; development is where in-progress changes land between them. To build from source on either branch, git checkout