Tesseron

Typed live-app actions for MCP-compatible AI agents, over WebSocket.

Built by BrainBlend AI

NEW: Join our community on Discord at discord.gg/J3W9b5AZJR — protocol questions, feedback, and SDK-contribution chat all welcome.

Live applications (browser tabs, Electron/Tauri desktop apps, Node daemons, CLIs) declare actions with a Zod-style builder; agents (Claude Code, Claude Desktop, Cursor, Copilot, Codex, Cline, ...) call them as MCP tools. Your real handler runs against your real state. No browser automation, no scraping, no Playwright.

Why Tesseron

• Typed actions, not scraped DOMs. Declare with Zod or any Standard Schema validator; the handler is a plain function against your real state.

• Framework-agnostic. Same API for vanilla TS, React, Svelte, Vue, and Node. Pick your stack.

• MCP-native. Every action, resource, and capability maps to a standard MCP primitive. Users pick their agent.

• Click-to-connect. Six-character claim code handshake. No API keys, no OAuth dance, no per-client configuration.

• First-class capabilities. ctx.confirm for yes/no, ctx.elicit for schema-validated prompts, ctx.sample for agent LLM calls, ctx.progress for streaming updates, subscribable resources for live reads.

• Bundled delivery. The MCP gateway ships inside a Claude Code plugin — one install command and you're done.

Quick install (Claude Code)

/plugin marketplace add BrainBlend-AI/tesseron
/plugin install tesseron@tesseron

That installs the tesseron Claude Code plugin, which spawns the MCP gateway automatically and registers it as an MCP server. Then drop @tesseron/web, @tesseron/server, or @tesseron/react into your app, declare actions, and let Claude drive your real UI.

import { tesseron } from '@tesseron/web';
import { z } from 'zod';

tesseron.app({ id: 'todo_app', name: 'Todo App' });

tesseron
  .action('addTodo')
  .input(z.object({ text: z.string().min(1) }))
  .handler(({ text }) => {
    state.todos.push({ id: newId(), text, done: false });
    render();
    return { ok: true };
  });

await tesseron.connect();

For other MCP clients (Claude Desktop, Cursor, Codex, VS Code Copilot, ...) see the one-time setup in examples/README.md.

See examples/ for working apps in vanilla TS, React, Svelte, Vue, Express, and plain Node.

Packages

The Claude Code plugin lives at plugin/, exposed via the marketplace manifest at .claude-plugin/marketplace.json.

Client capability support

Tesseron's action context gives handlers four capabilities beyond plain tool invocation, each backed by an MCP primitive. Whether a given call actually fires depends on what the user's MCP client advertises:

For the authoritative, continuously-updated list of which client supports which primitive, see the official MCP client compatibility matrix — filter by Sampling or Elicitation to see how narrow the field still is. A few points worth knowing before you pick a capability:

• Tools are universal — every MCP client can invoke your actions.

• Sampling is the rarest. Claude Code, Claude Desktop, and Claude.ai do not expose it; today's support is concentrated in VS Code + GitHub Copilot, goose, and fast-agent.

• Elicitation (MCP 2025-06) landed in Claude Code (2.1.76, March 2026), Cursor, Codex, VS Code Copilot, goose, and fast-agent, but not Claude Desktop, Claude.ai, ChatGPT, Windsurf, or Zed.

• When a capability is missing, Tesseron raises a typed error (SamplingNotAvailableError, ElicitationNotAvailableError) or collapses to the safe default (ctx.confirm returns false), so handlers can branch explicitly rather than silently misbehaving.

Status

v1.0 shipped April 2026. The protocol is stable at 1.0.0 and intentionally kept small: bidirectional JSON-RPC 2.0 over WebSocket, dynamic MCP tool registration, click-to-connect handshake, streaming progress, cancellation, sampling, confirmation, schema-validated elicitation, subscribable resources.

Published to npm (all at v1.0.1): @tesseron/core, @tesseron/web, @tesseron/server, @tesseron/react, @tesseron/mcp. The JS/TS SDKs are the reference implementation; the protocol spec is CC BY 4.0 so anyone can write a compatible client or server in any language.

On the roadmap: Svelte/Vue adapters, the devtools UI, a Streamable HTTP transport, a Python SDK, and bindings for desktop-native runtimes (Rust for Tauri, etc.).

Development

pnpm install
pnpm typecheck
pnpm test                                    # 65 tests across core + mcp
pnpm --filter @tesseron/mcp build:plugin     # rebuild plugin/server/index.cjs after gateway changes

Contributing

Bug reports, protocol refinements, new framework adapters, and improvements to the reference implementation are welcome.

• Read CONTRIBUTING.md for the workflow.

• Every commit must be Signed-off-by: under the Developer Certificate of Origin — use git commit -s.

• Open an issue first for anything larger than a small fix.

Star history

License

Reference implementation — Business Source License 1.1 (source-available). You may embed Tesseron in your own applications, use it internally, fork it, and redistribute it freely. You may not offer Tesseron or a substantial portion of it as a hosted or managed service to third parties. Each release auto-converts to Apache-2.0 four years after publication.

Protocol specification — CC BY 4.0. A compatible implementation in any language, for any purpose including commercial, is explicitly encouraged.

Contributions are welcome under the Developer Certificate of Origin — every commit must be Signed-off-by.