# Def Code — AI Developer CLI

> AI developer terminal with Plan, Build, Design, and Test modes. Repo-aware. Works in any language. Open-source Python SDK and MCP server.

## What it does

Def Code is an AI-powered command-line interface for developers. It reads your repository, understands your toolchain, and operates in four distinct modes — each tuned for a different stage of the development cycle.

## The four modes

### Plan mode
Proposes a scoped approach before any file change. Discusses the design, surfaces trade-offs, and asks clarifying questions. Use this when starting a new feature or refactor.

### Build mode
Implements reviewable diffs you can ship as a PR. Runs your tests, respects your linter, follows your existing patterns. The default mode for most work.

### Design mode
Generates UI scaffolding from a brief. Output respects your existing component library and design tokens.

### Test mode
Writes coverage for legacy code without changing behavior. Focuses on edge cases, error paths, and integration points.

## Languages supported

Def Code is language-agnostic with first-class support for:

- TypeScript / JavaScript (React, Next.js, Vue, Astro, etc.)
- Python (Django, FastAPI, Flask, data science stacks)
- Go (CLI tools, services, gRPC)
- Rust (systems, web, CLI)
- Swift (iOS, macOS)
- Kotlin (Android, JVM)

Plus working support for Ruby, Java, C#, PHP, C/C++, and shell.

## Developer integrations

- **Open-source Python SDK** — integrate Definable models and tools into your apps
- **MCP server** — expose Definable as a tool to any MCP-compatible client (Claude Desktop, Cursor, Windsurf, etc.)
- **REST + streaming API** — unified request shape across every supported model
- **Git-aware** — respects your branches, hooks, and commit conventions

## Use cases

- Pair programming on complex features
- Refactoring legacy code with safe, testable diffs
- Generating boilerplate that respects your codebase patterns
- Writing comprehensive test suites for untested code
- Building agents and tools against the Definable API

## Pricing

- Starter (free): limited
- Creator ($19/month): 1,000 lines/day
- Pro ($49/seat/month): unlimited, all 4 modes
- Enterprise (custom): VPC, BYO-key, on-prem

## Related

- HTML page: https://definable.ai/code/
- Pricing: https://definable.ai/pricing/
- Compare to Cursor: https://definable.ai/compare/definable-vs-cursor/
- Use case — AI for developers: https://definable.ai/use-cases/ai-for-developers/
- Glossary — What is MCP?: https://definable.ai/glossary/model-context-protocol-mcp/