The Software Intelligence Runtime.
Cursor, Codex, Claude Code — they all read your codebase cold, every session, and forget everything when it ends. Rune is the thing that runs underneath them, continuously, so every session starts already knowing your codebase instead of re-deriving it.
Without Rune:
flowchart LR
A1["New AI session"] --> A2["Reads files cold"]
A2 --> A3["Reasons, answers"]
A3 --> A4["Session ends"]
A4 -.->|"understanding lost"| A1
With Rune:
flowchart LR
B1["Code changes"] --> B2["rune watch rebuilds automatically"]
B2 --> B3["Understanding always current"]
B3 --> B4["New AI session"]
B4 --> B5["Queries Rune over MCP"]
B5 --> B6["Evidence-backed answer, cited to file + line"]
B6 -.->|"stays current"| B3
What it does · How it works · Install · Quickstart · See real output · CLI · MCP tools · Limitations · Security
Always current—rune watch
keeps the understanding graph up to date as you edit, not just when someone remembers to re-run a scan. It's a runtime, not a one-shot CLI.Persistent— understanding survives past any single session. Every AI you connect starts already knowing your software, instead of re-reading it cold.Shared— one understanding, many AI clients. Claude, GPT, Gemini, whatever you're running next month — they all ask the same Rune instance instead of maintaining separate, inconsistent mental models of your code.Explainable— nothing Rune tells an AI is a black box. Ask it to justify any claim and it shows the exact source location behind it.** Read-only, suggest-only**— Rune never writes to your source. That's the actual moat: everything else in this space is racing toward autonomous code-writing; Rune stays strictly on the reading, understanding, and (later) suggesting side of that line. It never becomes the thing you have to double-check for silently breaking your code.
Two layers, and every conclusion traces back to evidence — not asserted, always inspectable:
flowchart LR
F1["Fact: import react, UserCard.jsx line 1"] --> D["Derived: React component UserCard"]
F2["Fact: function UserCard, UserCard.jsx line 3"] --> D
F3["Fact: useState hook, UserCard.jsx line 4"] --> D
D --> C["AI answer: this project has a UserCard component"]
C -.->|"rune_explain"| F1
C -.->|"rune_explain"| F2
C -.->|"rune_explain"| F3
Call rune explain <id>
(or the rune_explain
MCP tool) on anything and get that chain back. An AI using Rune isn't guessing about your architecture — and neither is Rune.
npm install @pypl100/rune
A Python distribution exists at python/ with full feature parity (same fact/derived model, same detectors, same MCP tool surface) for teams who'd rather not require Node.js — published as pip install north-rune (the CLI command is still rune; see python/README.md).
If you install both(@pypl100/rune
via npm globally, andnorth-rune
via pip) on the same machine, only onerune
command will actually be on yourPATH
— whichever your shell finds first, not whichever you installed most recently. Check withwhich -a rune
; if it lists more than one path, that's why. There's no version-detection magic here — it's plain OSPATH
resolution, same as any two unrelated tools that happen to install a same-named binary. If you need a specific one, invoke it by its full path rather than relying on barerune
.
cd your-project
npm install -g @pypl100/rune # or: npx -p @pypl100/rune rune <command>
rune init # sets up Rune in your project
rune watch & # keeps the understanding current in the background as you work
rune serve # starts an MCP server exposing it to any AI client
rune watch
is the recommended default — it's what makes Rune a runtime instead of a tool you have to remember to re-run. (For CI or a one-shot check, use rune scan
instead.)
sequenceDiagram
participant Dev as You
participant Watch as rune watch
participant Graph as graph file
participant AI as AI client (Claude Code, Cursor, etc.)
Dev->>Watch: save a file
Watch->>Watch: detect change (debounced)
Watch->>Graph: rebuild + write
AI->>Graph: rune_search / rune_explain (via rune serve)
Graph-->>AI: current, evidence-backed answer
Point any MCP-compatible client (Claude Desktop, Claude Code, custom agents, etc.) at the rune serve
process. Every connected AI shares the same, continuously current understanding — no restart, no manual rescan.
Example MCP client config entry:
{
"mcpServers": {
"rune": {
"command": "npx",
"args": ["-p", "@pypl100/rune", "rune", "serve", "/absolute/path/to/your-project"]
}
}
}
Real output, from the fixture project in this repo — not staged:
$ rune scan .
[rune] scanned 4 file(s) in 34ms
[rune] facts: 10, derived conclusions: 4
[rune] graph written to /project/.rune/graph.json
$ rune explain component_2
{
"kind": "function",
"id": "component_2",
"type": "react_component",
"file": "components/UserCard.jsx",
"line": 3,
"name": "UserCard",
"evidence": "export function UserCard({ user }) {"
}
That's the whole trust model in one example: Rune doesn't just say "there's a UserCard
component" — it points at the exact file, the exact line, and the exact text it matched. Ask it to explain anything, and you get the receipts, not a claim.
| Command | What it does |
|---|---|
rune init [dir] |
|
Sets up .rune/ in the current (or given) project |
|
rune scan [dir] |
|
| Builds (or rebuilds) the understanding graph, once | |
rune watch [dir] |
|
| Keeps the understanding graph current as files change (Ctrl+C to stop) | |
rune serve [dir] |
|
| Starts the MCP server | |
rune explain <id> |
|
| Prints the evidence trail behind any fact or conclusion | |
rune --version |
|
| Prints the installed Rune version |
rune init
writes .rune/config.json
. The only setting today is ignore
— an array of directory/file names to exclude from scanning, on top of the built-in defaults (node_modules
, .git
, dist
, build
, .next
, coverage
, etc., and all dotfiles unconditionally):
{
"ignore": ["legacy", "vendor"],
"version": 1
}
| Tool | Purpose |
|---|---|
rune_get_overview |
|
| Architecture summary — start here | |
rune_list_components |
|
| All detected React components | |
rune_list_routes |
|
| Unified Express + Next.js route list | |
rune_search |
|
| Find facts/derived nodes by name, file, or route substring | |
rune_explain |
|
| Full evidence trail for any id | |
rune_get_file_dependencies |
|
| Internal import graph for a file | |
rune_rescan |
|
| Re-scan on demand after code changes |
Rune is intentionally narrow right now:
Framework support: React, Next.js (pages + app router), Express. Everything else gets generic file/import scanning only.Extraction method: heuristic, regex-based pattern matching — not a full AST parser. This keeps the scanner dependency-free and fast, and every fact still carries file/line/matched-text evidence, but it will miss unusual code shapes (e.g. components returned viaReact.createElement
with no JSX, dynamically constructed route strings, deeply re-exported components). A real AST-based extractor is the natural next upgrade — the fact schema is designed so extraction method can be swapped without touching anything downstream.No cross-file route-prefix resolution: an Express route mounted viaapp.use('/api', router)
in one file and defined in another isn't stitched into a single path yet.Read-only: Rune never writes to your source files. It only ever writes its own graph to.rune/graph.json
.Single-process, stdio MCP transport— no multi-client daemon yet.
- Rune
never scans dotfiles or dot-directories(
.env
,.env.*.js
,.git
,.ssh
, editor configs, etc.), with no exceptions. This is enforced in the scanner and covered by a regression test — a config file with a matching code extension (e.g..env.js
) will not have its contents read or embedded as evidence. - Symlinks are not traversed, so a symlink pointing outside the project root can't pull external files into the scan.
.rune/graph.json
is excluded from git byrune init
(it creates.gitignore
if one doesn't already exist).- The graph itself is the only thing Rune writes. If you share
.rune/graph.json
with an AI client, you're sharing everything in it — treat it like any other file that quotes snippets of your source.
The unit test suite (npm test
) covers scanning and the understanding graph, but doesn't spin up a real MCP client. scripts/verify-mcp-server.mjs
does: it spawns rune serve
as a real child process and drives it through the actual JSON-RPC handshake (initialize
→ notifications/initialized
→ tools/list
→ tools/call
), checks that all expected tools are exposed, and confirms a genuinely invalid call is rejected cleanly rather than crashing the server.
npm install
npm run verify:mcp
npm run verify:mcp -- /path/to/your-project
- AST-based extraction (swap-in replacement for the regex scanner)
- Cross-file route resolution
- Data-flow tracing between frontend calls and backend routes
- True incremental re-scan —
rune watch
exists now, but it still does a full rebuild on every change, not a diff of just what changed. Fine for small-to-medium projects; will matter on very large ones. - Suggestion tools (e.g. flagging a known-vulnerable dependency pattern with evidence, proposing a reviewable fix) — strictly additive to the read-only model, never auto-applied
MIT
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