MLX Code

A local AI coding assistant for macOS, powered by Apple MLX. No cloud. No subscriptions. No data leaving your machine.

MLX Code runs language models directly on Apple Silicon using the mlx-swift framework. It provides a chat interface with 14 built-in tools that can read files, search code, run shell commands, build Xcode projects, manage Git repos, and interact with GitHub – all driven by a local model running on your GPU.

Architecture

+-----------------------------------------------------------------------------------+
|                              MLX Code (macOS App)                                 |
|                                                                                   |
|  +---------------------------+    +--------------------------------------------+  |
|  |        SwiftUI Views      |    |              ViewModels                     |  |
|  |                           |    |                                            |  |
|  |  ChatView                 |    |  ChatViewModel                             |  |
|  |    MessageRowView         |    |    Conversation state & tool execution     |  |
|  |    CodeBlockView          |    |    Streaming token display                 |  |
|  |    CollapsibleToolResult  |    |    Slash command dispatch                  |  |
|  |    ToolApprovalView       |    |                                            |  |
|  |    ThinkingIndicatorView  |    |  ProjectViewModel                          |  |
|  |  CommandPalette           |    |    Build, archive, deploy operations       |  |
|  |  PromptTemplatesView      |    |                                            |  |
|  |  SettingsView             |    |  GitHubViewModel                           |  |
|  |  OnboardingView           |    |    Issues, PRs, branches                   |  |
|  |  DiffView                 |    |                                            |  |
|  |  GitHubPanelView          |    |  CodeAnalysisViewModel                     |  |
|  |  CodeAnalysisPanelView    |    |    Metrics, dependencies, lint             |  |
|  +---------------------------+    +--------------------------------------------+  |
|                |                                     |                            |
|                |           User messages              |                            |
|                +------------------+-------------------+                            |
|                                   |                                                |
|                                   v                                                |
|  +-------------------------------------------------------------------------+      |
|  |                         Tool Execution Layer                            |      |
|  |                                                                         |      |
|  |  ToolRegistry (14 tools, 2 tiers)                                       |      |
|  |  +-----------+  +-----------+  +----------+  +----------+  +---------+  |      |
|  |  | File Ops  |  |   Bash    |  |   Grep   |  |   Glob   |  |  Edit   |  |      |
|  |  +-----------+  +-----------+  +----------+  +----------+  +---------+  |      |
|  |       CORE           CORE          CORE          CORE          CORE     |      |
|  |                                                                         |      |
|  |  +-----------+  +-----------+  +----------+  +----------+  +---------+  |      |
|  |  |   Xcode   |  |    Git    |  |  GitHub  |  | CodeNav  |  |CodeAnal.|  |      |
|  |  +-----------+  +-----------+  +----------+  +----------+  +---------+  |      |
|  |  +-----------+  +-----------+  +----------+  +----------+               |      |
|  |  | ErrorDiag |  | TestGen   |  |DiffPreview| |   Help   |               |      |
|  |  +-----------+  +-----------+  +----------+  +----------+               |      |
|  |       DEVELOPMENT tier (available when a project is open)               |      |
|  +-------------------------------------------------------------------------+      |
|                                   |                                                |
|                                   v                                                |
|  +-------------------------------------------------------------------------+      |
|  |                          Inference Engine                               |      |
|  |                                                                         |      |
|  |  MLXService (Swift actor)                                               |      |
|  |    - Native mlx-swift-lm: LLMModelFactory + ModelContainer              |      |
|  |    - Chat templates via tokenizer (Jinja), flat-prompt fallback         |      |
|  |    - AsyncStream<Generation> for token streaming                        |      |
|  |    - SafeTensors-only model loading (PyTorch pickle rejected)           |      |
|  |    - Native HuggingFace Hub downloads (no Python)                       |      |
|  |                                                                         |      |
|  |  ContextManager (actor)           ContextBudget                         |      |
|  |    - Token estimation             - Budget allocation:                  |      |
|  |    - Message compaction             70% messages / 20% project /        |      |
|  |    - Project context inclusion      10% summary                         |      |
|  |                                                                         |      |
|  |  SystemPrompts                    UserMemories (actor)                  |      |
|  |    - ~500 token tool prompt       - 50+ built-in coding standards       |      |
|  |    - Compact tool descriptions    - 8 categories of rules               |      |
|  |    - Runtime memory injection     - Custom memories stored locally      |      |
|  +-------------------------------------------------------------------------+      |
|                                                                                   |
|  +-------------------------------------------------------------------------+      |
|  |                       Security & Utilities                              |      |
|  |                                                                         |      |
|  |  CommandValidator         ModelSecurityValidator    KeychainManager     |      |
|  |    - Regex pattern block    - SafeTensors only       - Secure storage   |      |
|  |    - Shell metachar filter  - Trusted sources        - API key mgmt     |      |
|  |    - Audit logging          - Hash verification                         |      |
|  |                                                                         |      |
|  |  SecureLogger             SecurityUtils              RepetitionDetector |      |
|  |    - Category-based logs    - Input sanitization     - Loop detection   |      |
|  |    - No PII in logs         - Command validation     - Auto-break       |      |
|  +-------------------------------------------------------------------------+      |
|                                                                                   |
+----------|---------------------|-----------------------|--------------------------+
           |                     |                       |
           v                     v                       v
+-------------------+  +-------------------+  +-------------------------+
| Xcode Extension   |  | Desktop Widget    |  | Nova API Server         |
|                   |  |                   |  |                         |
| 5 Editor commands |  | Small / Med / Lrg |  | HTTP on 127.0.0.1:37422 |
| Shared App Group  |  | Model status      |  |                         |
| mlxcode:// scheme |  | Token speed       |  | /api/status             |
|                   |  | Memory usage      |  | /api/chat               |
| Explain Selection |  | Quick actions     |  | /api/conversations      |
| Refactor          |  |                   |  | /api/model              |
| Generate Tests    |  | WidgetKit         |  | /api/metrics            |
| Fix Issues        |  | 5-min refresh     |  | /api/prompts            |
| Ask MLX Code      |  |                   |  | /api/cancel             |
+-------------------+  +-------------------+  +-------------------------+

Key design decisions:

Pure Swift inference – mlx-swift-lm framework, no Python dependency anywhere in the pipeline
Actor isolation – MLXService, ContextManager, and UserMemories are Swift actors for thread safety
SafeTensors only – PyTorch pickle files (.bin, .pt) are rejected at both discovery and load time
Compact prompts – Tool descriptions fit in ~500 tokens, not 4,000, leaving room for conversation
Two tool tiers – Core tools always available; development tools appear when a project is open
Budget-aware context – Token allocations: 70% recent messages, 20% project context, 10% summary

Features

Chat-Based Coding Assistant

Type a message, and the model reads files, searches code, runs commands, and builds your project. The 14 built-in tools cover the full development workflow:

Tool	Purpose	Tier
File Operations	Read, write, edit, list, delete files	Core
Bash	Run shell commands	Core
Grep	Search file contents with regex	Core
Glob	Find files by pattern	Core
Edit	Apply targeted file edits	Core
Xcode	Build, test, clean, archive, full deploy pipeline	Dev
Git	Status, diff, commit, branch, log, push, pull	Dev
GitHub	Issues, PRs, branches, credential scanning	Dev
Code Navigation	Jump to definitions, find symbols	Dev
Code Analysis	Metrics, dependencies, lint, symbols	Dev
Error Diagnosis	Analyze and explain build errors	Dev
Test Generation	Create unit tests from source files	Dev
Diff Preview	Show before/after file changes	Dev
Help	List available commands and usage	Dev

Read-only tools (grep, glob, file read, code navigation) auto-approve. Write and execute tools (bash, file write, xcode build) require confirmation.

Slash Commands

/commit    /review    /test      /docs
/refactor  /explain   /optimize  /fix
/search    /plan      /help      /clear

Xcode Source Editor Extension

Select code in Xcode and invoke from Editor > MLX Code:

Explain Selection – understand what code does
Refactor Selection – get an improved version
Generate Tests – write unit tests for the selection
Fix Issues – find and fix bugs
Ask MLX Code – open with code pre-loaded, ask anything

The extension communicates via a shared App Group container and the mlxcode:// URL scheme.

Prompt Engineering Toolkit

15 curated prompt templates across 9 categories, engineered for local LLMs (Qwen, Phi, Mistral). Browse templates, fill in variables, preview the rendered prompt, and send – all without leaving the app.

Category	Templates
Review	Swift Code Review, Review PR / Diff
Debug	Fix a Bug, Fix Build Error
Generate	Implement Feature, Add API Endpoint, Create Data Model
Refactor	Refactor File
Test	Add Unit Tests
Document	Add Documentation, Explain Code
Security	Security Audit, Add Error Handling
Performance	Performance Analysis
Deploy	Migration Plan

Three sizes (small, medium, large) showing model status, token speed, memory usage, and quick-action buttons that deep-link into the app.

GitHub Integration

The GitHub tool connects to the GitHub API to view and create issues, list and create pull requests, manage branches, and scan for exposed credentials before pushing.

User Memories

Persistent preferences that shape assistant behavior across conversations. 50+ built-in coding standards across 8 categories (personality, code quality, security, Xcode, git, testing, docs, deployment), plus custom memories stored locally. Injected into the system prompt at runtime – never hardcoded.

Context Management

Token budgeting with automatic message compaction when the context fills up
Real-time context window usage bar synced to the actual model’s context size
Project context auto-included when a workspace is open
Budget allocation: 70% recent messages, 20% project context, 10% summary of older messages

Syntax Highlighting

Code blocks render with syntax highlighting for Swift, Python, JavaScript, TypeScript, Bash, JSON, and Objective-C. Keywords, types, strings, comments, and numbers are all colored.

Nova API Server

MLX Code exposes a local HTTP API on port 37422 for integration with external tools and automations. The server binds to 127.0.0.1 only – no external network exposure.

GET  /api/status              App status, model loaded state, uptime
GET  /api/ping                Health check
GET  /api/conversations       List all conversations
GET  /api/conversations/:id   Single conversation with messages
POST /api/conversations       Create new conversation
DELETE /api/conversations/:id Delete conversation
POST /api/chat                Send a message, get response  {"message": "..."}
GET  /api/model               Current model info
POST /api/model/load          Load a model  {"model": "path"}
GET  /api/metrics             Performance metrics (tokens/sec, memory)
POST /api/cancel              Cancel current generation
GET  /api/prompts             List all prompt templates
GET  /api/prompts/:id         Get a template with variables
POST /api/prompts/render      Render template with filled variables

# Check status
curl -s http://127.0.0.1:37422/api/status | python3 -m json.tool

# Send a message
curl -X POST http://127.0.0.1:37422/api/chat \
  -H "Content-Type: application/json" \
  -d '{"message": "List all Swift files in this project"}'

# Browse prompt templates
curl -s http://127.0.0.1:37422/api/prompts | python3 -m json.tool

The API starts automatically when the app launches.

Screenshots

MLX Code main window

Models

MLX Code uses mlx-community models from Hugging Face, quantized for Apple Silicon.

Model	Size	Context	Best for
Qwen 2.5 7B (default)	~4 GB	32K	General coding, tool calling
Mistral 7B v0.3	~4 GB	32K	Versatile, good at instructions
DeepSeek Coder 6.7B	~4 GB	16K	Code-specific tasks
Qwen 2.5 14B	~8 GB	32K	Best quality (needs 16GB+ RAM)

Models download automatically on first use via the native Hub Swift API. You can also add custom models from any mlx-community repository.

All models must be in SafeTensors format. PyTorch pickle files (.bin, .pt) are rejected at both discovery and load time.

Requirements

macOS 14.0 (Sonoma) or later
Apple Silicon (M1, M2, M3, M4)
8 GB RAM minimum (16 GB recommended for 7B models)
No Python required – inference and downloads are pure Swift
Xcode 15+ – only needed for the Source Editor Extension feature

Installation

Quick Start

Download MLXCode-vX.Y.Z.dmg from Releases
Open the DMG and drag MLX Code to /Applications
Launch the app
Go to Settings > Models and download a model
Load the model and start chatting

Enabling the Xcode Extension

Open System Settings > Privacy & Security > Extensions > Xcode Source Editor
Enable MLX Code
Restart Xcode
Select code, then use Editor > MLX Code menu

See INSTALLATION.md for the full setup guide, including model paths, troubleshooting, and building from source.

Building from Source

git clone git@github.com:kochj23/MLXCode.git
cd MLXCode
open "MLX Code.xcodeproj"

Build the MLX Code scheme in Xcode 15+ targeting macOS 14.0+. The project uses Swift Package Manager for dependencies (mlx-swift, mlx-swift-lm, Hub).

Technical Details

Frameworks and Dependencies

Dependency	Purpose
mlx-swift	Apple MLX framework bindings for Swift
mlx-swift-lm	LLM inference: `LLMModelFactory`, `ModelContainer`, `GenerateParameters`
MLXLMCommon	Shared types: `UserInput`, `LMInput`, `AsyncStream<Generation>`
Hub	HuggingFace model downloads via `HubApi.snapshot()`
SwiftUI	All views, settings, onboarding, panels
WidgetKit	Desktop widget (3 sizes)
XcodeKit	Source Editor Extension
Network (NWListener)	Nova API HTTP server on loopback
CryptoKit	Model file hash verification
Security	Keychain storage for API keys

Concurrency Model

MLXService is a Swift actor – all model state (load, unload, generate) is automatically serialized
ContextManager and UserMemories are also actors
Token streaming uses AsyncStream<Generation>, delivered to @MainActor via MainActor.run
All background loops check Task.isCancelled for clean shutdown
Inference breaks immediately when </tool> is detected in output, preventing the model from running to maxTokens

Security

Shell Execution Safety:

CommandValidator blocks dangerous patterns (rm -rf /, fork bombs, sudo, eval, curl | sh) using regex word-boundary matching
Shell metacharacters (;, |, &, $, backticks) are rejected before pattern matching
Git and build tools use Process.currentDirectoryURL instead of string interpolation
Write/execute tools require user confirmation; read-only tools auto-approve

Model Security:

Only SafeTensors (.safetensors) format is permitted
PyTorch pickle files (.bin, .pt) are blocked – they can execute arbitrary Python code
ModelSecurityValidator verifies trusted sources and file hashes via CryptoKit

Data Privacy:

100% local inference – no prompts or responses leave your machine
No telemetry, analytics, or crash reporting
No cloud AI services (OpenAI, Anthropic, etc.)
The only external network calls are to the GitHub API, explicitly invoked by the user
User memories stored locally, never transmitted

What It Does Not Do

Being honest about limitations:

No web browsing – cannot fetch URLs or browse the internet
No image/video/audio generation – this is a code assistant
Small model constraints – 3-14B parameter models make mistakes, especially with complex multi-step reasoning
Tool calling is imperfect – local models sometimes format tool calls incorrectly (JSON auto-repair and retry help, but are not perfect)
Extension requires app switch – the Xcode extension opens MLX Code in a separate window rather than responding inline

Version History

Version	Date	Highlights
v6.4.0	April 2026	Prompt Engineering Toolkit – 15 templates, 9 categories, API endpoints, in-app browser
v6.3.0	March 2026	Xcode Source Editor Extension, native downloads (no Python), syntax highlighting, collapsed tool calls, accurate context bar, resume generation, SafeTensors-only loading
v6.2.0	March 2026	Replaced Python subprocess with native mlx-swift-lm inference, removed 2,726 lines of dead code
v6.1.x	March 2026	Security audit (31 findings resolved), Keychain migration, SecureLogger
v6.0.0	February 2026	GitHub integration, code analysis, Xcode deploy pipeline, user memories, 14 tools
v5.0.0	February 2026	Major simplification – deleted 41 files (~16,000 lines), compact system prompt, Qwen 2.5 default
v4.0.0	February 2026	Chat templates, tool tier system, context budgeting, tool approval flow
v1.x	Jan-Feb 2026	Initial release, MLX backend, desktop widget, basic chat

Roadmap

Deeper Xcode integration – write responses back into the editor buffer without switching apps
Structured output – grammar-constrained generation to guarantee well-formed tool calls from smaller models
Streaming download progress – real-time progress bar for model downloads

Project Structure

MLX Code/
  MLXCodeApp.swift                 App entry point
  Models/                          Data models (Message, Conversation, MLXModel, AppSettings)
  Services/
    MLXService.swift               Native MLX inference engine (actor)
    ContextManager.swift           Token budgeting and message compaction
    ContextBudget.swift            Budget allocation ratios
    NovaAPIServer.swift            HTTP API on port 37422
    GitHubService.swift            GitHub API client
    GitService.swift               Local git operations
    XcodeService.swift             Xcode build/test/archive
    UserMemories.swift             Persistent user preferences
    ConversationManager.swift      Conversation persistence
    FileService.swift              File system operations
    SessionManager.swift           Session lifecycle
    SlashCommandHandler.swift      Slash command dispatch
    XcodeActionHandler.swift       Handles requests from Xcode extension
    ModelSecurityValidator.swift   SafeTensors validation + hash checks
  Tools/
    ToolRegistry.swift             Central tool registry and dispatcher
    ToolProtocol.swift             Tool interface definition
    ToolTier.swift                 Core vs. development tier classification
    SystemPrompts.swift            System prompt generation with tool + memory injection
    PromptTemplates.swift          15 curated prompt templates
    BashTool.swift                 Shell command execution
    FileOperationsTool.swift       File CRUD
    GrepTool.swift                 Content search
    GlobTool.swift                 File pattern matching
    EditTool.swift                 Targeted file edits
    XcodeTool.swift                Build, test, archive, deploy
    GitIntegrationTool.swift       Git operations
    GitHubTool.swift               GitHub API tool
    CodeNavigationTool.swift       Symbol lookup and navigation
    CodeAnalysisTool.swift         Metrics, deps, lint
    ErrorDiagnosisTool.swift       Build error analysis
    TestGenerationTool.swift       Unit test generation
    DiffPreviewTool.swift          Before/after diff display
    HelpTool.swift                 Command help
    MemorySystem.swift             Tool execution memory
  Views/                           SwiftUI views (ChatView, SettingsView, etc.)
  ViewModels/                      ChatViewModel, ProjectViewModel, GitHubViewModel, etc.
  Utilities/
    CommandValidator.swift         Shell command security validation
    SecureLogger.swift             Category-based secure logging
    KeychainManager.swift          macOS Keychain wrapper
    SecurityUtils.swift            Input sanitization
    RepetitionDetector.swift       Detects and breaks inference loops
    BuildErrorParser.swift         Xcode build error parsing

MLX Code Extension/                Xcode Source Editor Extension (5 commands)
  SourceEditorExtension.swift      Extension entry point
  SourceEditorCommand.swift        Command handler, App Group IPC

MLX Code Widget/                   WidgetKit desktop widget (3 sizes)
  MLXCodeWidget.swift              Small, medium, large widget views
  SharedDataManager.swift          App Group data sync
  WidgetData.swift                 Widget data model

MLX Code Tests/                    Unit tests

License

See LICENSE for the full text.

Disclaimer

This is a personal project created on my own time. It is not affiliated with, endorsed by, or representative of my employer.

Written by Jordan Koch

MLX Code

Local LLM-powered coding assistant for macOS using Apple MLX framework — privacy-first alternative to GitHub Copilot. No cloud, no telemetry, runs entirely on Apple Silicon.

MLX Code

Architecture

Features

Chat-Based Coding Assistant

Slash Commands

Xcode Source Editor Extension

Prompt Engineering Toolkit

Desktop Widget (WidgetKit)

GitHub Integration

User Memories

Context Management

Syntax Highlighting

Nova API Server

Screenshots

Models

Requirements

Installation

Quick Start

Enabling the Xcode Extension

Building from Source

Technical Details

Frameworks and Dependencies

Concurrency Model

Security

What It Does Not Do

Version History

Roadmap

Project Structure

License

Disclaimer