@jlceda/mcli

⚠️ Preview Release: This is an early preview version. Expect frequent breaking changes until a stable release is published. APIs, commands, and behaviors may change without prior notice.

A command framework that serves one command tree through both shell and MCP — from a single definition with zero runtime dependencies.

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Install

npm install @jlceda/mcli

@jlceda/mcli ships with a single direct dependency — ajv(validated JSON Schema data) which is bundled into the ESM artifact at build time and requires no additional install from your host project.

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Quick Start

// app.ts
import { createMcli } from "@jlceda/mcli";

export const app = createMcli({
  name: "my-cli",
  version: "1.0.0",
});

const issue = app.group("issue", { summary: "Work with issues" });

issue.command("list", {
  summary: "List issues",
  description: "List issues from a repository.",

  input: {
    type: "object",
    properties: {
      repo: { type: "string", description: "Repository in owner/name format" },
      state: { type: "string", enum: ["open", "closed", "all"], default: "open" },
      limit: { type: "number", description: "Max results", default: 20 },
    },
    required: ["repo"],
  },

  examples: [
    {
      title: "List open issues",
      input: { repo: "acme/app", state: "open" },
    },
  ],

  handler: async (input) => {
    const issues = await fetchIssues(input);
    return {
      data: { issues },
      next: [{ path: "issue.get", reason: "Read issue detail" }],
    };
  },

  display: (result) => {
    const { issues } = result.data as any;
    console.log(`Found ${issues.length} issues`);
    for (const i of issues) {
      console.log(`  #${i.id}  ${i.state.padEnd(6)} ${i.title}`);
    }
  },
});

// bin.ts — your CLI entry
#!/usr/bin/env node
import { app } from "./app";
import { runCli } from "@jlceda/mcli";

await runCli(app, process.argv.slice(2));

# Human-readable (display callback invoked)
node bin.js issue list --repo acme/app
# Found 2 issues
#   1  open   Fix login
#   2  open   Add tests

# JSON (no display callback → fallback to JSON.stringify(result))
node bin.js issue list --repo acme/app --json
# { "ok": true, "path: "issue.list", "data": { "issues": [...] }, "next": [...] }

# MCP stdio
node bin.js --mcp stdio

# MCP stateless Streamable HTTP
node bin.js --mcp http --port 3030

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How it works

Progressive command registration

Commands are registered via group() binders — no dot-paths allowed:

const issue = app.group("issue", { summary: "Work with issues" });
issue.command("list", {...});   // CLI path: issue list, MCP path: issue.list
issue.command("close", {...});  // CLI path: issue close, MCP path: issue.close

// Nesting works too:
const sub = issue.group("label", { summary: "Label ops" });
sub.command("add", {...});      // CLI path: issue label add, MCP path: issue.label.add

app.command("foo.bar", ...) throws — you must use group binders for nesting.

The tree is the API

Every command is a node. The path issue.list maps to:

Layer	Reference
CLI argv	issue list
MCP call	{ path: "issue.list", input: {...} }
Shell help	my-cli issue list --help
Discovery	mcli.discover({ query: "list issues" })

MCP meta-tools (AI agent workflow)

Order	Tool	Purpose
1	mcli.help	ALWAYS call first. Returns subcommands, schemas, usage examples.
2	mcli.discover	Find specific commands by keyword after help.
3	mcli.call	Execute a command. Returns real data (search results, page content...).

Agent workflow:

Model: "what can this tool do?"
  → mcli.help()
  → { children: [{ path: "issue.list", summary: "..." }, ...] }

Model: "find issue-related commands"
  → mcli.discover({ query: "issue" })
  → [ { path: "issue.list", summary: "List issues" }, ... ]

Model: "list open issues for acme/app"
  → mcli.call({ path: "issue.list", input: { repo: "acme/app", state: "open" } })
  → { ok: true, data: { issues: [...] }, next: [{ path: "issue.get", reason: "Read detail" }] }

The next field in results suggests follow-up actions — chain tools naturally.

CLI output: display callback first

command has display? ─── yes → display(result)
      │
      no
      ├─ --json? → { ok, path, data, next }
      └─ default → JSON.stringify(result, null, 2)

display lets each command control its human-readable shape. The data field carries structured output for JSON consumers.

Transport protocols

Flag	Protocol	Use case
--mcp stdio	stdio	Local CLI tools, Claude Code, Cursor
--mcp http	stateless Streamable HTTP	Remote services, browser agents, multi-client

HTTP mode is stateless — each request creates a fresh transport, no session lifecycle. Optional --token for auth, --cors for browser access.

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API Reference

createMcli(opts)

function createMcli(opts: { name: string; version: string; summary?: string }): McliApp;

app.group(name, opts)

Returns a CommandGroup binder for progressive registration.

interface CommandGroup {
  command(name: string, opts: CommandOptions): void;
  group(name: string, opts: GroupOptions): CommandGroup;  // nesting
}

const github = app.group("github", {
  summary: "Work with GitHub",
  description: "Longer-form description.",
});

github.command("list", {...});  // path: github.list
const issue = github.group("issue", { summary: "Issues" });
issue.command("list", {...});   // path: github.issue.list

name — simple identifier, no dots allowed. Throws if contains ..

Idempotent — re-registering updates metadata.

app.command(name, opts)

Top-level command (no nesting). For nested commands, use app.group().command().

app.command("hello", {
  summary: "Say hello",
  input: { type: "object", properties: { name: { type: "string" } }, required: ["name"] },
  handler: async (input) => ({ data: { message: `Hello ${input.name}` } }),
});

name — simple identifier, no dots allowed. Throws if contains ..

interface CommandOptions {
  summary: string;
  description?: string;
  input: JSONSchema;
  examples?: CommandExample[];
  related?: string[];
  handler: (
    input: Record<string, unknown>,
    ctx: CommandContext,
  ) => Promise<CommandResult> | CommandResult;
  display?: (result: CommandResult) => void;
}

input — JSON Schema. Validation via ajv. default values are filled before handler runs.

examples — Each example's input is validated against the command's input schema at registration time. Invalid examples throw immediately.

handler receives:

• input — validated + default-filled object
• ctx — { services?: Record<string, unknown> } (reserved)

handler returns:

interface CommandResult {
  data?: unknown; // structured output
  next?: Array<{ path: string; reason: string }>; // Agent hints for follow-up
}

display — optional CLI renderer. Receives the CommandResult. Not used in MCP mode.

app.resolve(argv) / app.allCommands()

Look up a node (returns null if unknown) / list all leaf commands (used by discover).

runCli(app, argv)

CLI driver. Call from your own bin entry:

await runCli(app, process.argv.slice(2));

Handles --help / --search / --json / --mcp dispatch, plus direct command invocation.

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JSON input shape

Commands declare input as JSON Schema. Supported:

Kind	Example
string	{ type: "string", description: "..." }
number	{ type: "number" }
boolean	{ type: "boolean" }
enum	{ type: "string", enum: ["open", "closed"] }
object (nested)	{ type: "object", properties: { ... }, required: [...] }
optional	omit from required
default	{ type: "number", default: 20 }

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Error handling

# Shell (text)
Error: (root): must have required property 'repo'

# Shell (--json)
{
  "ok": false,
  "path": "issue.list",
  "error": {
    "code": "VALIDATION_ERROR",
    "message": "(root): must have required property 'repo'",
    "details": [{ "field": "(root)", "message": "must have required property 'repo'" }]
  }
}

# MCP (mcli.call)
{ "isError": true, "content": [...] }

Error class	Code
McliValidationError	input failed JSON Schema
McliExecutionError	handler threw / missing handler

Registration-time errors:

• Dot in command/group name → "Command(name) must not contain dots. Use app.group() to nest commands."
• Invalid example input → throws immediately on command() call

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Direct dependencies

@jlceda/mcli ships with a single direct dependency — ajv (JSON Schema validator), which is bundled into the ESM artifact (dist/index.js) at build time.

Host projects install nothing extra beyond @jlceda/mcli.

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Build / publish

npm run build    # dist/index.js + dist/index.d.ts
npm test         # vitest, 62 tests
npm pack         # produce tarball

Ships only dist/. @jlceda/mcli → dist/index.js.

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License

MIT