Repl Toolkit

A .NET framework for building composable command surfaces.

• Define your commands once — run them as a CLI, explore them in an interactive REPL,
• host them in session-based terminals, expose them as MCP servers and MCP Apps for AI agents,
• or drive them from automation scripts.

New here? Start at repl.yllibed.org — installation, your first app, guides, cookbook, and API reference.

Quick start

dotnet add package Repl

using Repl;

var app = ReplApp.Create().UseDefaultInteractive();
app.Map("hello", () => "world");
return app.Run(args);

Example

using Repl;

var app = ReplApp.Create().UseDefaultInteractive();

app.Context("client", client =>
{
    client.Map("list", () => new { Clients = new[] { "ACME", "Globex" } });

    client.Context("{id:int}", scoped =>
    {
        scoped.Map("show", (int id) => new { Id = id, Name = "ACME" });
        scoped.Map("remove", (int id) => Results.Cancelled($"Remove {id} cancelled."));
    });
});

return app.Run(args);

CLI mode:

$ myapp client list --json
{
  "clients": ["ACME", "Globex"]
}

REPL mode (same command graph):

$ myapp
> client 42 show --json
{ "id": 42, "name": "ACME" }

> client
[client]> list
ACME
Globex

MCP mode (same command graph, exposed to AI agents):

using Repl.Mcp;

app.UseMcpServer();  // add one line

{ "command": "myapp", "args": ["mcp", "serve"] }

MCP Apps (same server, host-rendered UI for capable clients):

app.Map("contacts dashboard", (IContactStore contacts) => BuildHtml(contacts))
    .WithDescription("Open the contacts dashboard")
    .AsMcpAppResource();

One command graph. CLI, REPL, remote sessions, and AI agents — all from the same code.

What's included

Feature	Package	Docs
Unified command graph — routing, constraints, binding		Routes & Parameters Pipelining & Integration Cookbook: Core Basics
Interactive REPL — scopes, history, autocomplete		REPL Mode Configuration Cookbook: Scoped Contexts
Parameters & options — typed binding, options groups, response files		Routes & Parameters Built-in Types & Formats
Multiple output formats — JSON, XML, YAML, Markdown		Customization & Output
MCP server + MCP Apps — expose commands as agent tools, resources, prompts, and UI		MCP Mode MCP In Depth Agent-Native Development Cookbook: MCP Server
Typed results & interactions — prompts, progress, cancellation		Interactivity Cookbook: Interactive Prompts
Session hosting — WebSocket, Telnet, remote terminals		Cookbook: Hosting Remote Sessions Terminal Integration
Shell completion — Bash, PowerShell, Zsh, Fish, Nushell		CLI Mode
Spectre.Console — rich prompts, tables, charts		Cookbook: Spectre.Console Interactivity
Testing toolkit — in-memory multi-session harness		Cookbook: Testing
Machine-readable contracts — help schemas, error contracts		Best Practices & FAQ
Conditional modules — channel-aware, feature-gated commands		Modules Cookbook: Modular Ops

Repl is the meta-package that bundles Core + Defaults + Protocol — start here.

Learn by example

Progressive learning path — each sample builds on the previous. Each sample has a companion cookbook page with explanations and patterns.

Sample	Cookbook
Core Basics — routing, constraints, help, output modes	repl.yllibed.org/cookbook/core-basics/
Scoped Contacts — dynamic scoping, .. navigation	repl.yllibed.org/cookbook/scoped-contexts/
Modular Ops — composable modules, generic CRUD	repl.yllibed.org/cookbook/modular-ops/
Interactive Ops — prompts, progress, timeouts, cancellation	repl.yllibed.org/cookbook/interactive-prompts/
Hosting Remote — WebSocket / Telnet session hosting	repl.yllibed.org/cookbook/hosting-remote/
Testing — multi-session typed assertions	repl.yllibed.org/cookbook/testing/
Spectre — Spectre.Console renderables, visualizations, rich prompts	repl.yllibed.org/cookbook/spectre/
MCP Server — MCP tools, resources, prompts, and MCP Apps UI	repl.yllibed.org/cookbook/mcp-server/

More documentation

Architecture	Best Practices & FAQ
Coming from CLI frameworks	Packaging & Distribution
Packages overview	API Reference
Glossary	Dependency Injection

AI-assisted development

If you use an AI coding agent (Claude Code, Cursor, Windsurf, Copilot, Codex, OpenCode, etc.) to build your Repl Toolkit app, install Context7 to give it access to Repl Toolkit documentation and code snippets.

Library ID: /yllibed/repl

Most agents that support MCP can use Context7 directly. Refer to your agent's documentation for MCP server configuration.

Contributing

Contributions welcome — please discuss new features first to keep the toolkit aligned with its goals. See CONTRIBUTING.md, CODE_OF_CONDUCT.md, and SECURITY.md.

License

MIT — Copyright (c) 2026 Yllibed project / Carl de Billy