Tesseron

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

Tesseron is an accessibility layer for AI agents. You instrument your app once — the way you'd add ARIA to a web page — and any MCP-compatible agent can drive it through typed actions you define. Think of it as an API for agents, written by the people who built the app.

The premise: the agent doesn't need to click a button, it needs to do the thing the button does. Say an agent wants to add five items to a list. Through the UI that's click add, type, submit, click add again — five round-trips through a brittle, re-render-happy interface. With Tesseron it calls one action:

addTodos(['buy milk', 'finish report', 'call mom', 'book flight', 'water plants'])

Your handler runs against your real state. No clicking, no scraping, no brittleness.

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 in your real process, against your real state. No browser automation, no scraping, no Playwright.

It's a protocol, not just a TypeScript library — and not just for the web. The JS/TS SDKs are the reference implementation and already cover the browser, Node, and desktop (Electron/Tauri). But the wire protocol is CC BY 4.0 and language-agnostic: anything that can open a WebSocket and speak JSON-RPC 2.0 can host actions, so a Python daemon, a Rust desktop app, or a .NET line-of-business tool can speak it too. Web is simply where the first SDKs landed — not the boundary of what Tesseron is.

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.
• Cross-client delivery. First-class install paths for Claude Code, Codex, OpenCode, and Pi — each one a single command or short config snippet that wires the MCP gateway in. No bundled binary; the gateway is npx -y @tesseron/mcp@<version> on demand.

Install

Tesseron has first-class install paths for four agent clients. Pick the one you use:

Claude Code

/plugin marketplace add eigenwise/tesseron
/plugin install tesseron@tesseron

Installs the tesseron Claude Code plugin. The MCP gateway and docs server are launched on demand via npx.

Codex CLI

codex plugin marketplace add eigenwise/tesseron

Codex consumes the same plugin manifest as Claude Code, so the gateway, docs server, and skills come along automatically.

Pi

Pi has no built-in MCP support, but the community-maintained pi-mcp-adapter is the canonical bridge. Install it once:

pi install npm:pi-mcp-adapter

Then add Tesseron to .mcp.json in your project root (or ~/.config/mcp/mcp.json for a global install):

{
  "mcpServers": {
    "tesseron": { "command": "npx", "args": ["-y", "@tesseron/[email protected]"] },
    "tesseron-docs": { "command": "npx", "args": ["-y", "@tesseron/[email protected]"] }
  }
}

pi-mcp-adapter discovers and exposes the Tesseron tools to Pi automatically. Use "directTools": true per server entry to surface each Tesseron action as a top-level Pi tool instead of going through the mcp proxy.

To pick up the skill bundle as well, point Pi's settings skills array at a clone of plugin/skills/ — the same folder Claude Code / Codex use.

OpenCode

OpenCode reads MCP servers from opencode.json rather than a plugin manifest. Save this as .opencode/opencode.json in your project root (or ~/.config/opencode/opencode.json for global use):

{
  "$schema": "https://opencode.ai/config.json",
  "mcp": {
    "tesseron": { "type": "local", "command": ["npx", "-y", "@tesseron/[email protected]"], "enabled": true },
    "tesseron-docs": { "type": "local", "command": ["npx", "-y", "@tesseron/[email protected]"], "enabled": true }
  }
}

To also pick up the skill bundle, point OpenCode's skills.paths at a clone of plugin/skills/ — see plugin/README.md for the snippet.

Other MCP clients

Claude Desktop, Cursor, VS Code Copilot, Cline, and any other MCP-compatible client work too — the gateway is plain stdio MCP. See the one-time setup in examples/README.md.

Then in your app

Drop @tesseron/web, @tesseron/server, @tesseron/react, @tesseron/svelte, or @tesseron/vue into your project, declare actions, and let the agent 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();

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

Packages

Package	Purpose
@tesseron/core	Protocol types, action builder. Zero runtime deps beyond Standard Schema.
@tesseron/web	Browser SDK.
@tesseron/server	Node SDK.
@tesseron/react	React hooks adapter.
@tesseron/svelte	Svelte 5 adapter.
@tesseron/vue	Vue 3 adapter.
@tesseron/vite	Vite plugin: dev-server bridge for browser tabs to dial the gateway over the same origin as your app.
@tesseron/mcp	MCP gateway server (tesseron-mcp CLI; launched by each client's install path via npx).
@tesseron/docs-mcp	MCP server that serves the Tesseron docs (search_docs, read_doc, list_docs) for chapter-and-verse spec lookups inside agent sessions.

The Claude Code / Codex plugin lives at plugin/, exposed via the marketplace manifests at .claude-plugin/marketplace.json (Claude) and .agents/plugins/marketplace.json (Codex).

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:

SDK surface	MCP primitive
tool(...) (action invocation)	tools
resource(...) (live reads, subscriptions)	resources (+ resources.subscribe)
ctx.sample(...)	sampling
ctx.confirm(...) / ctx.elicit(...)	elicitation
ctx.progress(...)	notifications/progress (client must pass _meta.progressToken on tools/call)

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 SDK is at v2.10 as of writing. 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, session resume.

Published to npm: all nine packages — @tesseron/{core,web,server,react,svelte,vue,vite,mcp,docs-mcp} — ship in lockstep at the same version (currently 2.10.0). 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: a Streamable HTTP transport, a Python SDK, and bindings for desktop-native runtimes (Rust for Tauri, etc.).

Development

pnpm install
pnpm typecheck
pnpm test                            # vitest across core + mcp
pnpm lint                            # biome
pnpm sync-plugin-version --check     # CI guard: plugin manifests + Pi pin + skill mirror in lockstep

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.

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Built and maintained by Eigenwise.
© 2026 Kenny Vaneetvelde.