@tesseron/core

Protocol types and action builder for Tesseron — a TypeScript SDK + MCP gateway that exposes typed web-app actions to MCP-compatible AI agents (Claude Code, Claude Desktop, Cursor, Copilot, Codex, ...) over a local WebSocket.

Most users don't install @tesseron/core directly. Reach for one of the framework-targeted packages instead:

Package	Use when
@tesseron/web	You're in a browser app (any framework)
@tesseron/server	You're in Node (CLI, daemon, Express, Fastify, ...)
@tesseron/react	You want hook-based React integration

Install @tesseron/core directly only if you're building a custom transport, a third-party framework adapter, or a compatible Tesseron SDK in another language — the protocol spec is CC BY 4.0, reimplementations are explicitly encouraged.

What's inside

• Protocol types — JSON-RPC 2.0 wire shapes (HelloParams, WelcomeResult, ActionInvokeParams, etc.), method and notification names, TesseronCapabilities, the discriminated TransportSpec + InstanceManifest types for the multi-binding discovery format, and the versioned PROTOCOL_VERSION constant (currently 1.1.0).
• Action builder — the fluent, typed .action(name).input(schema).handler(fn) API that the framework packages wrap.
• Resource builder — subscribable or read-only resources with the same fluent ergonomics.
• Handler context — ActionContext with ctx.confirm, ctx.elicit, ctx.sample, ctx.progress, ctx.log, cancellation via ctx.signal, and the negotiated ctx.agentCapabilities.
• Typed error hierarchy — TesseronError + SamplingNotAvailableError, ElicitationNotAvailableError, SamplingDepthExceededError, TimeoutError, CancelledError, TransportClosedError, all with MCP-mapped error codes in TesseronErrorCode.
• Transport interface — the four-method contract a custom transport must implement.

Install

npm install @tesseron/core

Zero runtime dependencies beyond @standard-schema/spec (types only).

Example — custom transport

import { TesseronClient, type Transport } from '@tesseron/core';
import { z } from 'zod';

class InMemoryTransport implements Transport {
  send(message: unknown) { /* ... */ }
  onMessage(handler: (m: unknown) => void) { /* ... */ }
  onClose(handler: (reason?: string) => void) { /* ... */ }
  close(reason?: string) { /* ... */ }
}

const client = new TesseronClient();
client.app({ id: 'shop', name: 'Shop' });

client
  .action('addItem')
  .input(z.object({ sku: z.string() }))
  .handler(({ sku }, ctx) => {
    ctx.log({ level: 'info', message: `adding ${sku}` });
    return { ok: true };
  });

await client.connect(new InMemoryTransport());

For the real browser and Node transports, see @tesseron/web and @tesseron/server.

Docs

License

Reference implementation — Business Source License 1.1 (source-available). Each release auto-converts to Apache-2.0 four years after publication. Protocol specification — CC BY 4.0.

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