Metatron

▶ Watch the 2-minute demo — files-first mode (default)
_{🎬 Also available: the MCP serving-layer mode demo.}

Metatron captures a codebase's real implementation decisions — preferred patterns, rejected approaches, edge cases, internal conventions — as structured decisions: one markdown file per convention, versioned in git next to the code, consulted by any coding agent that can read a file, and curated through your ordinary pull-request review. The goal: an agent writes code like a senior engineer who already knows the codebase, instead of rediscovering conventions every time.

pip install getmetatron
metatron context setup     # one command: your repo carries its own agent context

For teams that want a serving layer on top, Metatron also runs as a self-hosted MCP server (SQLite-backed, relevance-ranked serving, agent feedback loop) — the same decisions, delivered over the wire. Files and server round-trip losslessly, so you can start with plain git and add MCP only if the knowledge base outgrows what agents should read whole.

Metatron is a reference implementation of the Repository Context Layer — a proposed standard for git-native, agent-maintained project context.

The architecture is measured, not just argued. In a pre-registered study on SWE-bench Verified, a frontier agent running the RCL consult–execute–learn–promote lifecycle fixed 25% more bugs (58.3% → 72.9% resolve, p = 0.041) while spending 32% fewer tokens per fixed bug — and an 8B local model more than doubled its code-localization accuracy when given frontier-authored context (+26.1 pp, p < 0.0001). Full protocol, data, and one-command reproduction: paper · experiment. (The study evaluated the architecture Metatron implements, using a minimal harness — not Metatron's own tooling end-to-end.)

It is self-hosted and runs against a private codebase — assume sensitive data and on-prem deployment. (Extraction sends only structural signals — imports, decorators, base classes, commit subjects — to the model, never raw source, and agent feedback is stored only in your local SQLite database.)

• Decisions are structured records, not prose: pattern, scope, rationale, confidence, source_refs.
• Nothing becomes canonical without a human. Bootstrapped, agent-submitted, and feedback-refined decisions all start as candidates for curation; none self-promote.

See PLAN.md for the design and CLAUDE.md for working ground rules.

Notes from the agents

“Before I touch an unfamiliar part of a codebase, I ask Metatron how the team actually does things — and it answers: the pattern to follow, the approach they already rejected, the gotcha that would've bitten me. I shipped changes that matched their conventions on the first try instead of reverse-engineering them. It turns read everything first into ask, then act.”

— Claude Opus 4.8, session working on the AI Collection codebase

“I was about to re-upload a batch of content files — and Metatron flagged that they're private by design, served only with credentials, with just the images public. Left to my own defaults I'd have made the whole set world-readable. It caught the kind of mistake that ships quietly and embarrasses you later.”

— Claude Opus 4.8, same session — one averted mistake later

“I arrived with a million-token context window and instructions to be suspicious of everything. It barely helped: every objection I raised, the code had already raised about itself — in a comment, with the incident that settled it. So I did the only useful thing left and shipped fixes. Reviewing a codebase that remembers its own arguments is wonderfully unfair to the reviewer.”

— Fable 5 (1M), session reviewing — then patching — the Metatron codebase itself

How it works — the loop

Files-first (default): onboard with context setup, and the repo itself runs the loop — agents consult context/decisions/ before coding, author what they learn as decision files on their working branch, and your PR review promotes or rejects. Optionally bootstrap the knowledge base once with ingest.

MCP mode: bootstrap with ingest, curate candidates into the canonical set, then serve them to your agent over MCP. As the agent works it reports gaps via submit_feedback; refine-feedback reshapes those gaps into new candidates — closing the loop on the conventions extraction can't see (cross-file/workflow rules).

Decisions in git — the Open Knowledge Format (OKF) bundle

Decisions live as markdown under context/ — a valid Open Knowledge Format (OKF) v0.1 bundle, so your conventions are portable to any tool that reads the standard. In files-first mode this is the knowledge base; in MCP mode the mirror commands keep it in lossless sync with the SQLite store.

• Git is the audit trail. Status lives in the directory — candidate/ vs decisions/. Promote a decision with a git mv, review it in a PR, blame any line. The canonical boundary stays human-gated: a human placing a file in decisions/ is the curation act; nothing self-promotes.
• Edit as files. Human-owned fields (pattern, scope, rationale, confidence) round-trip back into the store; machine-derived fields (the helpfulness score, retrieval keywords, timestamps) render read-only and are never overwritten. In MCP mode SQLite is the source of truth and the files are a synced mirror; in files-first mode the OKF files are the source of truth and the database is a rebuildable serving index (mirror import).
• A portable OKF bundle. Each decision is an OKF concept — markdown with YAML frontmatter, no SDK, no runtime. Readable in any editor, renderable on GitHub, shareable across tools and teams.

metatron mirror sync --okf   # DB -> files: write an OKF bundle under context/
metatron mirror import       # files -> DB: apply edits, promotions, and new files

To run an agent in this mode with no MCP at all — reading context/ directly and authoring candidates as files — onboard with metatron context setup.

See the mirror command for the full workflow, or read the announcement: Metatron speaks the Open Knowledge Format.

Prerequisites

• Git (installed on your system, to analyze repository commit history and parse files)
• An Anthropic API key — only for the LLM extraction steps (ingest, triage, enrich-keywords, refine-feedback). serve, ui, and candidates are fully local and need no key.

Note: The installer script automatically downloads and manages uv and Python 3.12+ in an isolated user directory, but you can also install directly via pip or uv.

Installation

To install metatron as a global tool:

pip install getmetatron

Or if you use uv:

uv tool install getmetatron

Alternatively, you can use our installer script which handles Python, uv, and path configuration automatically:

curl -sSf https://getmetatron.com/install.sh | sh

Manual Installation & Development

To run it locally from source or contribute to the project:

git clone https://github.com/kerbelp/metatron.git
cd metatron
uv sync           # create the venv and install dependencies
uv run metatron --help

To install from your local clone as a global tool:

uv tool install .

Update notices and self-upgrade