A powerful, extensible AI coding agent CLI with multi-provider support, built-in tools, and a rich extension system.
Features
- Multi-Provider LLM Support: Anthropic, OpenAI, Google Gemini, Ollama, Azure OpenAI, AWS Bedrock, OpenRouter, and more
- Built-in Core Tools: bash (with interactive sudo password prompt), read, write, edit, grep, find, ls, subagent - no MCP overhead
- Smart @ Attachments: Binary files auto-detected via MIME type, MCP resources via
@mcp:server:uri
- MCP Integration: Connect external MCP servers for expanded capabilities
- Extension System: Write custom tools, commands, widgets, and UI modifications in Go
- Theming: 22 built-in color themes (KITT, Catppuccin, Dracula, Nord, etc.) with runtime switching, persistence, and custom theme files
- Model Persistence: Model and thinking level selections are automatically saved and restored across sessions
- Prompt Templates: Create reusable prompt templates with shell-style argument substitution
- Interactive TUI: Rich terminal interface powered by Bubble Tea with streaming, syntax highlighting, and custom rendering
- Session Management: Tree-based conversation history with branching support
- Non-Interactive Mode: Script-friendly positional args with JSON output
- ACP Server: Run Kit as an Agent Client Protocol agent over stdio
- Go SDK: Embed Kit in your own applications
Installation
Using npm / bun / pnpm
npm install -g @mark3labs/kit
# or
bun install -g @mark3labs/kit
# or
pnpm install -g @mark3labs/kit
Using Go
go install github.com/mark3labs/kit/cmd/kit@latest
Building from source
git clone https://github.com/mark3labs/kit.git
cd kit
go build -o kit ./cmd/kit
Quick Start
Basic Usage
# Start interactive session
kit
# Run a one-off prompt
kit "List files in src/"
# Attach files as context
kit @main.go @test.go "Review these files"
# Continue the most recent session
kit --continue
# Model and thinking level selections are automatically persisted
# across sessions and restored on next launch
# Use specific model
kit --model anthropic/claude-sonnet-latest
Non-Interactive Mode
# Get JSON output for scripting
kit "Explain main.go" --json
# Quiet mode (final response only)
kit "Run tests" --quiet
# Ephemeral mode (no session file)
kit "Quick question" --no-session
ACP Server Mode
Kit can run as an ACP (Agent Client Protocol) agent server, enabling ACP-compatible clients (such as OpenCode) to drive Kit as a remote coding agent over stdio.
# Start Kit as an ACP server (communicates via JSON-RPC 2.0 on stdin/stdout)
kit acp
# With debug logging to stderr
kit acp --debug
The ACP server exposes Kit's full capabilities — LLM execution, tool calls (bash, read, write, edit, grep, etc.), and session persistence — over the standard ACP protocol. Sessions are persisted to Kit's normal JSONL session files, so they can be resumed later.
Configuration
Kit looks for configuration in the following locations (in order of priority):
- CLI flags
- Environment variables (with
KIT_ prefix)
./.kit.yml / ./.kit.yaml / ./.kit.json (project-local)
~/.kit.yml / ~/.kit.yaml / ~/.kit.json (global)
Basic Configuration
Create ~/.kit.yml:
model: anthropic/claude-sonnet-latest
max-tokens: 4096
temperature: 0.7
stream: true
thinking-level: off # off, none, minimal, low, medium, high
All of the above keys can also be set programmatically via the SDK
(kit.Options.MaxTokens, Options.Temperature, Options.ThinkingLevel, etc.)
without touching config files — see SDK options.
Environment Variables
export ANTHROPIC_API_KEY="sk-..."
export OPENAI_API_KEY="sk-..."
export KIT_MODEL="openai/gpt-4o"
MCP Server Configuration
Add external MCP servers to .kit.yml:
mcpServers:
filesystem:
type: local
command: ["npx", "-y", "@modelcontextprotocol/server-filesystem", "/path/to/allowed"]
environment:
LOG_LEVEL: "info"
allowedTools: ["read_file", "write_file"]
search:
type: remote
url: "https://mcp.example.com/search"
CLI Reference
Global Flags
# Model and provider
--model, -m Model to use (provider/model format)
--provider-api-key API key for the provider
--provider-url Base URL for provider API
--tls-skip-verify Skip TLS certificate verification
# Session management
--session, -s Open specific JSONL session file
--continue, -c Resume most recent session for current directory
--resume, -r Interactive session picker
--no-session Ephemeral mode, no persistence
# Behavior (non-interactive: pass prompt as positional arg)
--quiet Suppress all output (non-interactive only)
--json Output response as JSON (non-interactive only)
--no-exit Enter interactive mode after prompt completes
--max-steps Maximum agent steps (0 for unlimited)
--stream Enable streaming output (default: true)
--compact Enable compact output mode
--auto-compact Auto-compact conversation near context limit
# Extensions
--extension, -e Load additional extension file(s) (repeatable)
--no-extensions Disable all extensions
--prompt-template Load a specific prompt template by name
--no-prompt-templates Disable prompt template loading
# Generation parameters
--max-tokens Maximum tokens in response (default: 8192, auto-raised up to 32768 for models with larger known output limits)
--temperature Randomness 0.0-1.0 (default: 0.7)
--top-p Nucleus sampling 0.0-1.0 (default: 0.95)
--top-k Limit top K tokens (default: 40)
--stop-sequences Custom stop sequences (comma-separated)
--frequency-penalty Penalize frequent tokens 0.0-2.0 (default: 0.0)
--presence-penalty Penalize present tokens 0.0-2.0 (default: 0.0)
--thinking-level Extended thinking level: off, none, minimal, low, medium, high (default: off)
# System
--config Config file path (default: ~/.kit.yml)
--system-prompt System prompt text or file path
--debug Enable debug logging
Commands
# Authentication (for OAuth-enabled providers)
kit auth login [provider] # Start OAuth flow (e.g., anthropic)
kit auth logout [provider] # Remove credentials for provider
kit auth status # Check authentication status
# Model database
kit models [provider] # List available models (optionally filter by provider)
kit models --all # Show all providers (not just LLM-compatible)
kit update-models [source] # Update model database (from models.dev, URL, file, or 'embedded')
# Extension management
kit extensions list # List discovered extensions
kit extensions validate # Validate extension files
kit extensions init # Generate example extension template
kit install <git-url> # Install extensions from git repositories
kit install -l <git-url> # Install to project-local .kit/git/ directory
kit install -u <git-url> # Update an already-installed package
kit install --uninstall <pkg> # Remove an installed package
# Skills
kit skill # Install the Kit extensions skill via skills.sh
# ACP server
kit acp # Start as ACP agent (stdio JSON-RPC)
kit acp --debug # With debug logging to stderr
Themes
Kit ships with 22 built-in color themes that control all UI elements. Switch at runtime:
/theme dracula
/theme catppuccin
/theme tokyonight
Theme selections are automatically saved and restored on next launch (stored in ~/.config/kit/preferences.yml). This persistence also applies to model and thinking level selections — all are saved together and restored on startup.
Custom themes
Drop a .yml file in ~/.config/kit/themes/ (user) or .kit/themes/ (project):
# ~/.config/kit/themes/my-theme.yml
primary:
light: "#8839ef"
dark: "#cba6f7"
success:
light: "#40a02b"
dark: "#a6e3a1"
Built-in themes: kitt, catppuccin, dracula, tokyonight, nord, gruvbox, monokai, solarized, github, one-dark, rose-pine, ayu, material, everforest, kanagawa, amoled, synthwave, vesper, flexoki, matrix, vercel, zenburn
Extension System
Extensions are Go source files that run via Yaegi interpreter. They can add custom tools, slash commands, widgets, keyboard shortcuts, themes, and intercept lifecycle events.
Minimal Extension
//go:build ignore
package main
import "kit/ext"
func Init(api ext.API) {
api.OnSessionStart(func(_ ext.SessionStartEvent, ctx ext.Context) {
ctx.SetFooter(ext.HeaderFooterConfig{
Content: ext.WidgetContent{Text: "Custom Footer"},
})
})
}
Usage:
kit -e examples/extensions/minimal.go
Extension Capabilities
Lifecycle Events: OnSessionStart, OnSessionShutdown, OnBeforeAgentStart, OnAgentStart, OnAgentEnd, OnToolCall, OnToolExecutionStart, OnToolOutput, OnToolExecutionEnd, OnToolResult, OnInput, OnMessageStart, OnMessageUpdate, OnMessageEnd, OnModelChange, OnContextPrepare, OnBeforeFork, OnBeforeSessionSwitch, OnBeforeCompact, OnCustomEvent, OnSubagentStart, OnSubagentChunk, OnSubagentEnd
Custom Components:
- Tools: Add new tools the LLM can invoke
- Commands: Register slash commands (e.g.,
/mycommand)
- Options: Register configurable extension options
- Widgets: Persistent status displays above/below input
- Headers/Footers: Persistent content above/below the conversation
- Status Bar: Custom status bar entries
- Shortcuts: Global keyboard shortcuts
- Overlays: Modal dialogs with markdown content
- Tool Renderers: Customize how tool calls display
- Message Renderers: Custom rendering for assistant messages
- Editor Interceptors: Handle key events and wrap rendering
- Interactive Prompts: Select, confirm, input, and multi-select dialogs
- Subagents: Spawn in-process child Kit instances
- LLM Completion: Direct model calls via
Complete()
- Themes: Register and switch color themes via
RegisterTheme, SetTheme, ListThemes
- Custom Events: Inter-extension communication via
EmitCustomEvent
Bridged SDK APIs (NEW): Extensions can now access internal SDK capabilities:
- Tree Navigation: Navigate conversation history (
GetTreeNode, GetCurrentBranch, NavigateTo), summarize branches (SummarizeBranch), and implement fresh context loops (CollapseBranch)
- Skill Loading: Dynamically load and inject skills at runtime (
LoadSkill, DiscoverSkills, InjectSkillAsContext)
- Template Parsing: Parse and render templates with
{{variables}} (ParseTemplate, RenderTemplate), parse CLI-style arguments (ParseArguments, SimpleParseArguments), and evaluate model conditionals (EvaluateModelConditional, RenderWithModelConditionals)
- Model Resolution: Resolve model fallback chains (
ResolveModelChain), query model capabilities (GetModelCapabilities, CheckModelAvailable), and extract provider/model ID (GetCurrentProvider, GetCurrentModelID)
Extension Examples
See the examples/extensions/ directory:
Also see .kit/extensions/go-edit-lint.go (in this repo) for a project-local extension example that runs gopls and golangci-lint on Go file edits.
Loading Extensions
Auto-discovery (loads automatically):
~/.config/kit/extensions/*.go (global single files)
~/.config/kit/extensions/*/main.go (global subdirectory extensions)
.kit/extensions/*.go (project-local single files)
.kit/extensions/*/main.go (project-local subdirectory extensions)
~/.local/share/kit/git/ (global git-installed packages)
.kit/git/ (project-local git-installed packages)
Explicit loading:
kit -e path/to/extension.go
kit -e ext1.go -e ext2.go # Multiple extensions
Disable auto-load:
kit --no-extensions
Testing Extensions
Kit provides a testing package to help you write unit tests for your extensions:
package main
import (
"testing"
"github.com/mark3labs/kit/pkg/extensions/test"
"github.com/mark3labs/kit/internal/extensions"
)
func TestMyExtension(t *testing.T) {
harness := test.New(t)
harness.LoadFile("my-ext.go")
// Emit events and verify behavior
_, err := harness.Emit(extensions.SessionStartEvent{SessionID: "test"})
if err != nil {
t.Fatalf("unexpected error: %v", err)
}
// Verify the extension printed something
test.AssertPrinted(t, harness, "session started")
}
Available assertions:
AssertBlocked(), AssertNotBlocked() — Verify tool blocking
AssertWidgetSet(), AssertWidgetText() — Verify widget content
AssertPrinted(), AssertPrintedContains() — Verify output
AssertToolRegistered(), AssertCommandRegistered() — Verify registration
See examples/extensions/tool-logger_test.go for a complete example with 14 test cases covering tool calls, input handling, and session lifecycle.
Prompt Templates
Create reusable prompt templates with shell-style argument substitution. Templates are loaded from ~/.kit/prompts/*.md and .kit/prompts/*.md.
Example template (~/.kit/prompts/review.md):
---
description: Review code for issues
---
Review the following code for bugs and security issues.
Focus on $1 specifically.
Usage:
/review error handling
Argument placeholders:
$1, $2, etc. — Individual arguments
$@ or $ARGUMENTS — All arguments (zero or more)
$+ — All arguments (one or more required; error if none given)
${@:2} — Arguments from position 2 onwards
${@:1:3} — 3 arguments starting at position 1
Placeholders inside fenced code blocks (```) and inline code spans are ignored.
Disable templates with --no-prompt-templates or load a specific template with --prompt-template <name>.
Session Management
Kit uses a tree-based session model that supports branching and forking conversations.
Session Locations
- Default:
~/.kit/sessions/<cwd-path>/<timestamp>_<id>.jsonl
- Path separators in the working directory are replaced with
-- (e.g., /home/user/project becomes home--user--project)
- Each line is a session entry (messages, tool calls, extension data)
- Supports branching from any message to explore alternate paths
Session Commands
# Resume most recent session for current directory
kit --continue
kit -c
# Interactive session picker
kit --resume
kit -r
# Open specific session file
kit --session path/to/session.jsonl
kit -s path/to/session.jsonl
# Ephemeral mode (no file persistence)
kit --no-session
Interactive Session Commands
During an interactive session, use these slash commands:
| Command |
Description |
/name [name] |
Set or display the session's display name |
/session |
Show session info (path, ID, message count) |
/resume |
Open the session picker to switch sessions |
/export [path] |
Export session as JSONL (auto-generates path if omitted) |
/import <path> |
Import and switch to a session from a JSONL file |
/share |
Upload session to GitHub Gist and get a shareable viewer URL |
/tree |
Navigate the session tree |
/fork |
Fork to new session from an earlier message |
/new |
Start a fresh session |
Keyboard Shortcuts
| Shortcut |
Description |
Ctrl+X e |
Open $VISUAL/$EDITOR to compose or edit your prompt |
Ctrl+X s |
Steer — inject a system-level instruction mid-turn |
ESC ESC |
Cancel the current operation (tool call or streaming) |
↑ / ↓ |
Navigate prompt history |
Go SDK
Embed Kit in your Go applications:
package main
import (
"context"
"log"
kit "github.com/mark3labs/kit/pkg/kit"
)
func main() {
ctx := context.Background()
// Create Kit instance with default configuration
host, err := kit.New(ctx, nil)
if err != nil {
log.Fatal(err)
}
defer func() { _ = host.Close() }()
// Send a prompt
response, err := host.Prompt(ctx, "What is 2+2?")
if err != nil {
log.Fatal(err)
}
println(response)
}
With Options
host, err := kit.New(ctx, &kit.Options{
Model: "ollama/llama3",
SystemPrompt: "You are a helpful bot",
ConfigFile: "/path/to/config.yml",
MaxSteps: 10,
Streaming: true,
Quiet: true,
// Generation parameters (override env/config/per-model defaults)
MaxTokens: 16384, // 0 = auto-resolve (env → config → per-model → 8192 floor)
ThinkingLevel: "medium", // "off", "none", "minimal", "low", "medium", "high"
Temperature: ptr(float32(0.2)), // pointer so 0.0 != unset; nil = provider default
TopP: nil, // nil = leave provider/per-model default
TopK: nil,
FrequencyPenalty: nil,
PresencePenalty: nil,
// Provider configuration (override env/config without reaching into viper)
ProviderAPIKey: "sk-...", // "" = use config / provider env var
ProviderURL: "https://proxy.internal/v1", // "" = provider default
TLSSkipVerify: false, // only takes effect when true
// Session options
SessionPath: "./session.jsonl", // Open specific session
Continue: true, // Resume most recent session
NoSession: true, // Ephemeral mode
// Tool options
Tools: []kit.Tool{...}, // Replace default tool set entirely
ExtraTools: []kit.Tool{...}, // Add tools alongside defaults
DisableCoreTools: true, // Use no core tools (0 tools, for chat-only)
// Configuration
SkipConfig: true, // Skip .kit.yml files (viper defaults + env vars still apply)
// Compaction
AutoCompact: true, // Auto-compact near context limit
Debug: true, // Debug logging
})
Generation & provider fields (added in v0.55+) let SDK consumers configure
Kit entirely in-code without viper.Set() workarounds or shipping a .kit.yml.
Precedence is Options > KIT_* env vars > .kit.yml > per-model defaults
(modelSettings / customModels) > provider-level defaults. Sampling params
are pointer types so explicit 0.0 is distinguishable from "leave alone"; a
non-zero MaxTokens suppresses automatic right-sizing the same way --max-tokens
does on the CLI.
MCP OAuth (remote MCP servers)
When a remote MCP server returns 401, Kit runs the full OAuth flow (dynamic
client registration → PKCE → token exchange → persistence) but delegates the
user-facing step — showing the authorization URL and receiving the callback —
to an MCPAuthHandler that you pass explicitly via Options.MCPAuthHandler.
If nil, OAuth is disabled and the authorization-required error surfaces to the
caller; the SDK never auto-opens a browser or binds a localhost port.
// CLI/TUI apps: opens the system browser + prints status to stderr.
authHandler, _ := kit.NewCLIMCPAuthHandler()
defer authHandler.Close()
host, _ := kit.New(ctx, &kit.Options{
MCPAuthHandler: authHandler,
})
// Custom UX: reuse the SDK's port + callback server, supply your own
// presentation via OnAuthURL (TUI modal, QR code, web redirect, etc.).
// h, _ := kit.NewDefaultMCPAuthHandler()
// h.OnAuthURL = func(server, authURL string) { myUI.Show(server, authURL) }
//
// Full control (web apps, daemons): implement kit.MCPAuthHandler yourself —
// no localhost binding, no side effects.
Tokens are persisted to $XDG_CONFIG_HOME/.kit/mcp_tokens.json by default; swap
in a custom MCPTokenStoreFactory for encrypted, DB-backed, or in-memory
storage. See the SDK options docs for
the full matrix.
Create custom tools with automatic schema generation — no external dependencies needed:
type SearchInput struct {
Query string `json:"query" description:"Search query"`
}
searchTool := kit.NewTool("search", "Search the codebase",
func(ctx context.Context, input SearchInput) (kit.ToolOutput, error) {
return kit.TextResult("Found: ..."), nil
},
)
host, _ := kit.New(ctx, &kit.Options{
ExtraTools: []kit.Tool{searchTool}, // adds alongside built-in tools
})
Use kit.NewParallelTool for tools safe to run concurrently. See the SDK docs for full details on struct tags, ToolOutput fields, and ToolCallIDFromContext.
With Callbacks
unsub := host.OnToolCall(func(e kit.ToolCallEvent) {
println("Calling tool:", e.ToolName)
})
defer unsub()
unsub2 := host.OnToolResult(func(e kit.ToolResultEvent) {
if e.IsError {
println("Tool failed:", e.ToolName)
}
})
defer unsub2()
unsub3 := host.OnStreaming(func(e kit.MessageUpdateEvent) {
print(e.Chunk)
})
defer unsub3()
response, err := host.Prompt(
ctx,
"List files in current directory",
)
Session Management
// Multi-turn conversations retain context automatically
host.Prompt(ctx, "My name is Alice")
response, _ := host.Prompt(ctx, "What's my name?")
// Sessions are persisted automatically to JSONL files.
// Access session info:
path := host.GetSessionPath()
id := host.GetSessionID()
// Clear conversation history
host.ClearSession()
Session persistence is configured via Options:
host, _ := kit.New(ctx, &kit.Options{
SessionPath: "./my-session.jsonl", // Open specific session
Continue: true, // Resume most recent session
NoSession: true, // Ephemeral mode
})
Advanced Usage
Subagent Pattern
Spawn Kit as a subprocess for multi-agent orchestration:
kit "Analyze codebase" \
--json \
--no-session \
--no-extensions \
--quiet \
--model anthropic/claude-haiku-3-5-20241022
Parse the JSON output:
{
"response": "Final assistant response text",
"model": "anthropic/claude-haiku-3-5-20241022",
"stop_reason": "end_turn",
"session_id": "a1b2c3d4e5f6",
"usage": {
"input_tokens": 1024,
"output_tokens": 512,
"total_tokens": 1536,
"cache_read_tokens": 0,
"cache_creation_tokens": 0
},
"messages": [
{
"role": "assistant",
"parts": [
{"type": "text", "data": "..."},
{"type": "tool_call", "data": {"name": "...", "args": "..."}},
{"type": "tool_result", "data": {"name": "...", "result": "..."}}
]
}
]
}
Testing with tmux
Test the TUI non-interactively:
# Start Kit in detached tmux session
tmux new-session -d -s kittest -x 120 -y 40 \
"kit -e ext.go --no-session 2>kit.log"
# Wait for startup
sleep 3
# Capture screen
tmux capture-pane -t kittest -p
# Send input
tmux send-keys -t kittest '/command' Enter
# Cleanup
tmux kill-session -t kittest
Development
Build and Test
# Build
go build -o output/kit ./cmd/kit
# Run tests
go test -race ./...
# Run specific test
go test -race ./cmd -run TestScriptExecution
# Lint
go vet ./...
# Format
go fmt ./...
Project Structure
cmd/kit/ - CLI entry point (main.go)
cmd/ - CLI command implementations (root, auth, models, etc.)
pkg/kit/ - Go SDK for embedding Kit
internal/app/ - Application orchestrator (agent loop, message store, queue)
internal/agent/ - Agent execution and tool dispatch
internal/auth/ - OAuth authentication and credential storage
internal/acpserver/ - ACP (Agent Client Protocol) server
internal/clipboard/ - Cross-platform clipboard operations
internal/compaction/ - Conversation compaction and summarization
internal/config/ - Configuration management
internal/core/ - Built-in tools (bash, read, write, edit, grep, find, ls)
internal/extensions/ - Yaegi extension system
internal/kitsetup/ - Initial setup wizard
internal/message/ - Message content types and structured content blocks
internal/models/ - Provider and model management
internal/session/ - Session persistence (tree-based JSONL)
internal/skills/ - Skill loading and system prompt composition
internal/tools/ - MCP tool integration
internal/ui/ - Bubble Tea TUI components
examples/extensions/ - Example extension files
npm/ - NPM package wrapper for distribution
Supported Providers
- Anthropic - Claude models (native, prompt caching, OAuth)
- OpenAI - GPT models
- Google - Gemini models
- Ollama - Local models
- Azure OpenAI - Azure-hosted OpenAI
- AWS Bedrock - Bedrock models
- Google Vertex - Claude on Vertex AI
- OpenRouter - Multi-provider router
- Vercel AI - Vercel AI SDK models
- Custom - Any OpenAI-compatible endpoint via
--provider-url
- Auto-routed - Any provider from models.dev database
Custom Provider
Use custom/custom when pointing Kit at any OpenAI-compatible endpoint with --provider-url:
kit --provider-url "http://localhost:8080/v1" "Hello"
This automatically defaults to custom/custom without needing to specify a model. The custom provider routes through the openaicompat provider and supports:
- Zero cost tracking (input/output = 0)
- 262K context window, 65K output limit
- Reasoning and temperature support
- Optional
CUSTOM_API_KEY environment variable or --provider-api-key flag
provider/model # Standard format
anthropic/claude-sonnet-latest
openai/gpt-4o
ollama/llama3
google/gemini-2.0-flash-exp
Model Aliases
# Anthropic Claude
claude-opus-latest → claude-opus-4-6
claude-sonnet-latest → claude-sonnet-4-6
claude-haiku-latest → claude-haiku-4-5
claude-4-opus-latest → claude-opus-4-6
claude-4-sonnet-latest → claude-sonnet-4-6
claude-4-haiku-latest → claude-haiku-4-5
claude-3-7-sonnet-latest → claude-3-7-sonnet-20250219
claude-3-5-sonnet-latest → claude-3-5-sonnet-20241022
claude-3-5-haiku-latest → claude-3-5-haiku-20241022
claude-3-opus-latest → claude-3-opus-20240229
# OpenAI GPT
o1-latest → o1
o3-latest → o3
o4-latest → o4-mini
gpt-5-latest → gpt-5.4
gpt-5-chat-latest → gpt-5.4
gpt-4-latest → gpt-4o
gpt-4 → gpt-4o
gpt-3.5-latest → gpt-3.5-turbo
gpt-3.5 → gpt-3.5-turbo
codex-latest → codex-mini-latest
# Google Gemini
gemini-pro-latest → gemini-2.5-pro
gemini-flash-latest → gemini-2.5-flash
gemini-flash → gemini-2.5-flash
gemini-pro → gemini-2.5-pro
Contributing
Contributions are welcome! Please see the contribution guide for guidelines.
License
MIT