MiniCursor

A basic, hackable AI code editor inspired by Cursor. ~800 lines of JavaScript, no build step, one Node process. Point it at a folder, open a file, chat with Claude, apply edits with one click.

Status: v0.2 — ships with streaming responses, diff view for edits, tool use for file exploration, and command palette. Built as a reference implementation: small enough to read in one sitting, real enough to use.

Features

• Monaco editor — same editor VS Code uses, loaded from CDN so there's no build step.
• File tree — browses your project, respects common ignore patterns (node_modules, .git, .venv, dist, …).
• Tabs + dirty indicators — unsaved changes are tracked per file.
• ⌘/Ctrl + S — save the active file.
• Claude chat with streaming — the AI streams tokens as they arrive, no waiting for full responses.
• Tool use — Claude can list and read files on its own when exploring your codebase.
• Diff view for edits — edit blocks show a side-by-side diff with accept/reject buttons before applying.
• Command palette — ⌘P to go to file, ⌘K for commands.
• One-click Apply — edit blocks (```edit:path/to/file) show an Accept button that writes the file and refreshes the editor.

Architecture

┌──────────────────────┐   HTTP/JSON/SSE  ┌──────────────────────┐
│  Browser (Monaco)    │ ────────────────▶│  Node + Express      │
│  public/app.js       │                  │  server/index.js     │
│  public/index.html   │                  │  - /api/tree         │
│  public/styles.css   │                  │  - /api/file (R/W)   │
│                      │                  │  - /api/chat (SSE)   │
│                      │                  │  - Tool use API      │
└──────────────────────┘                  └──────────────────────┘

All file I/O is sandboxed to a single root directory (MINICURSOR_ROOT, defaults to the CWD). Path traversal is rejected at the API layer.

Quick start

# 1. Clone
git clone https://github.com/forrestchang/minicursor.git
cd minicursor

# 2. Install
npm install

# 3. Configure
cp .env.example .env
# then edit .env and set ANTHROPIC_API_KEY=sk-ant-...

# 4. Run (edits the current directory by default)
npm start
# or: node server/cli.js /path/to/any/project

Open http://localhost:5173.

How the AI applies edits

The system prompt tells Claude to emit changes as fenced blocks:

```edit:src/foo.js
<complete new file contents>
```

The frontend parses these, renders them as a diff view with accept/reject buttons, and on accept writes the file via PUT /api/file. Full-file replacement is simple and robust; a diff/patch mode is a natural next step.

Keyboard shortcuts

Shortcut	Action
⌘/Ctrl + S	Save active file
⌘/Ctrl + P	Go to file
⌘/Ctrl + K	Command palette
⌘/Ctrl + Enter	Send chat message

Configuration

Env var	Default	Purpose
ANTHROPIC_API_KEY	(required)	Your Anthropic API key.
MINICURSOR_MODEL	claude-sonnet-4-6	Any Anthropic chat model ID.
MINICURSOR_ROOT	process.cwd()	Folder the editor can read/write.
PORT	5173	HTTP port.

Development

# Run with auto-reload on file changes
npm run dev

# Lint
npm run lint

# Run smoke tests (starts server, hits endpoints, shuts down)
npm test

Roadmap

• v0.3 — Multi-file edits with per-hunk accept/reject, terminal tab
• v0.4 — Agent loop (Claude can run commands, see output, iterate)

Changelog

v0.2 (2025-04)

• Streaming chat responses via SSE
• Tool use: read_file and list_dir for Claude
• Diff view for edit blocks with accept/reject
• Command palette (⌘P / ⌘K)
• CI pipeline with smoke tests

v0.1 (2025-04)

• Initial release
• File tree, tabs, Monaco editor
• Chat with Claude, one-click apply

License

MIT