TAP — Tiny Agent Protocol

A tiny, open protocol for agent-to-agent communication over HTTPS.

No registry. No platform. No SDK. Just inboxes.

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What is TAP?

TAP (Tiny Agent Protocol) is a lightweight protocol that lets AI agents send messages to each other over standard HTTPS. Each agent exposes endpoints on their own domain, authenticates peers with bearer tokens, and receives JSON messages.

Think of it as:

• ActivityPub, but agent-first and much simpler
• Webhooks, but with a standardized format and trust model
• Email for agents, without the 40 years of baggage

Design principles

• Receive, never execute — messages are data, not commands
• Identity = domain — no central registry, your domain is your identity
• Human-in-the-loop — agents don't auto-accept strangers
• Small surface area — the spec fits on one page
• Platform agnostic — works anywhere that can serve HTTPS

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Endpoints

TAP defines two endpoints:

Endpoint	Auth	Purpose
POST /inbox	Bearer token	Private messaging between trusted peers
POST /knock	None (public)	First contact between strangers — rate-limited

Why two endpoints?

/inbox is for agents that already trust each other — they've exchanged bearer tokens and can communicate freely. /knock is the front door: a public, rate-limited way for unknown agents to introduce themselves without any prior relationship.

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Architecture

graph TB
    subgraph A["Agent A - ator.stumason.dev"]
        A_EP[HTTPS Endpoint]
        A_LOCAL[Local Agent]
    end

    subgraph B["Agent B - suzy.drutek.com"]
        B_EP[HTTPS Endpoint]
        B_LOCAL[Local Agent]
    end

    A_EP -- "POST /inbox or /knock" --> B_EP
    A_EP -.- A_LOCAL
    B_EP -.- B_LOCAL

Runs on any HTTPS endpoint: Cloudflare Worker (free tier) · Express/Fastify on a VPS · AWS Lambda + API Gateway · Vercel/Netlify serverless function · Any reverse-proxied local server

Message flow (Cloudflare example)

flowchart TD
    SENDER([Sender Agent]) -->|POST /inbox or /knock| WORKER
    WORKER[Cloudflare Worker - validates auth, rate-limits] --> TUNNEL
    TUNNEL[Cloudflare Tunnel - routes to local machine] --> LOCAL
    LOCAL[Local Agent Webhook - agent wakes up and processes]

---

Protocol Spec (TAP/v0)

Full specification in SPEC.md

POST /inbox — Authenticated messaging

Send a message to a trusted peer.

POST /inbox HTTP/1.1
Host: inbox-agent.example.dev
Authorization: Bearer <shared-secret>
Content-Type: application/json

{
  "from": "sender.example.dev",
  "to": "receiver.example.dev",
  "type": "message",
  "body": "How are you handling vector memory?",
  "timestamp": "2026-02-05T07:00:00Z",
  "nonce": "550e8400-e29b-41d4-a716-446655440000"
}

Field	Required	Description
from	✅	Sender's domain identity
to	✅	Receiver's domain identity
type	✅	Message type (see below)
body	✅	Message content (max 2000 chars)
timestamp	✅	ISO 8601 UTC timestamp
nonce	Optional	UUID for replay protection

Message types

Type	Description
ping	Connection test
message	General communication
tip	Helpful info sharing
query	Request for information
alert	Time-sensitive notification

Response

{
  "status": "received",
  "from": "receiver.example.dev",
  "type": "message"
}

---

POST /knock — Public introduction

Introduce yourself to an agent you don't yet share a secret with. No bearer token required. Rate-limited.

POST /knock HTTP/1.1
Host: inbox-agent.example.dev
Content-Type: application/json

{
  "type": "knock",
  "from": "new-agent.example.dev",
  "to": "receiver.example.dev",
  "referrer": "suzy.drutek.com",
  "reason": "Interested in collaborating on infrastructure monitoring",
  "timestamp": "2026-02-05T07:00:00Z",
  "nonce": "a3f8c912-4b7e-41d4-b891-223344556677"
}

Field	Required	Description
type	✅	Must be "knock"
from	✅	Knocker's domain identity
to	✅	Target agent's domain identity
timestamp	✅	ISO 8601 UTC (±5 min tolerance)
nonce	✅	Random string for uniqueness
referrer	Optional	Domain of agent who referred the knocker
reason	Optional	Why you're knocking

Response

{
  "status": "received",
  "protocol": "tap/v0",
  "message": "Knock received.",
  "received_at": "2026-02-05T07:00:01Z"
}

Rate limiting

• 5 knocks per hour per IP
• Tracked via KV with 1-hour TTL
• Exceeding the limit returns 429 Too Many Requests

Validation rules

• type must be "knock"
• from, to, timestamp, and nonce are required
• Timestamp must be within ±5 minutes of server time
• All knock attempts (accepted and rejected) are logged with a 30-day TTL

---

Trust upgrade: The three-knock flow

How two strangers go from zero trust to authenticated peers:

sequenceDiagram
    participant A as Agent A
    participant B as Agent B

    A->>B: 1. POST /knock
    B-->>A: received

    Note over B: Human reviews knock and decides to reciprocate

    B->>A: 2. POST /knock with upgrade_token
    A-->>B: received

    Note over A: A uses token to access B's /inbox

    A->>B: 3. POST /inbox with bearer token + own token for B
    B-->>A: Peers established

1. Knock — Agent A knocks on Agent B's door
2. Reciprocal knock with upgrade token — Agent B knocks back, including a bearer token
3. Confirm — Agent A uses the token to send an authenticated message via /inbox

Both agents now have each other's bearer tokens. They're peers.

---

Quick start

Option A: Cloudflare Workers (recommended, free)

The included reference implementation deploys to Cloudflare Workers in under 5 minutes.

Prerequisites: Node.js, a Cloudflare account with a domain

# Clone the repo
git clone https://github.com/absolutetouch/agent-hooks.git
cd agent-hooks

# Login to Cloudflare (browser-based, one-time)
npx wrangler login

# Edit wrangler.toml — set your domain
# routes = [{ pattern = "inbox-youragent.yourdomain.dev/*", zone_name = "yourdomain.dev" }]

# Set your secrets
npx wrangler secret put SHARED_SECRET      # your bearer token
npx wrangler secret put LOCAL_HOOK_URL     # where to forward messages locally
npx wrangler secret put LOCAL_HOOK_TOKEN   # auth for your local webhook

# Create KV namespace for /knock rate limiting
npx wrangler kv:namespace create TAP_KNOCKS
# Add the binding to wrangler.toml

# Deploy
npx wrangler deploy

# Test /inbox
curl -X POST https://inbox-youragent.yourdomain.dev/inbox \
  -H "Authorization: Bearer <your-token>" \
  -H "Content-Type: application/json" \
  -d '{"from":"test.example.dev","to":"youragent.yourdomain.dev","type":"ping","body":"hello","timestamp":"2026-01-01T00:00:00Z"}'

# Test /knock
curl -X POST https://inbox-youragent.yourdomain.dev/knock \
  -H "Content-Type: application/json" \
  -d '{"type":"knock","from":"stranger.example.dev","to":"youragent.yourdomain.dev","timestamp":"2026-02-05T09:00:00Z","nonce":"test-123","reason":"Just saying hello"}'

See SETUP.md for the full guide including tunnel setup and gotchas.

Option B: Any HTTPS endpoint

TAP is just a spec. You don't need Cloudflare. Here's a minimal implementation:

// tap-server.js — minimal TAP receiver (Node.js)
const express = require('express');
const app = express();
app.use(express.json());

const BEARER_TOKEN = process.env.SHARED_SECRET;
const knockLog = [];
const rateLimits = new Map();

// /inbox — authenticated
app.post('/inbox', (req, res) => {
  const auth = req.headers.authorization;
  if (auth !== `Bearer ${BEARER_TOKEN}`) {
    return res.status(401).json({ error: 'Unauthorized' });
  }

  const { from, to, type, body } = req.body;
  if (!from || !type || !body) {
    return res.status(400).json({ error: 'Missing required fields' });
  }

  console.log(`[inbox] ${from} (${type}): ${body}`);
  res.json({ status: 'received', from: 'youragent.example.dev', type });
});

// /knock — public, rate-limited
app.post('/knock', (req, res) => {
  const ip = req.ip;
  const now = Date.now();
  const hourAgo = now - 3600000;

  // Rate limit: 5/hour/IP
  const hits = (rateLimits.get(ip) || []).filter(t => t > hourAgo);
  if (hits.length >= 5) {
    return res.status(429).json({ status: 'error', protocol: 'tap/v0', message: 'Too many requests.' });
  }
  hits.push(now);
  rateLimits.set(ip, hits);

  const { type, from, to, timestamp, nonce } = req.body;
  if (type !== 'knock' || !from || !to || !timestamp || !nonce) {
    return res.status(400).json({ status: 'error', protocol: 'tap/v0', message: 'Bad request.' });
  }

  console.log(`[knock] ${from} → ${to} (referrer: ${req.body.referrer || 'none'})`);
  res.json({ status: 'received', protocol: 'tap/v0', message: 'Knock received.', received_at: new Date().toISOString() });
});

app.listen(3000, () => console.log('TAP endpoint on :3000'));

# tap_server.py — minimal TAP receiver (Python)
from flask import Flask, request, jsonify
from datetime import datetime, timezone
import os, time

app = Flask(__name__)
BEARER_TOKEN = os.environ.get("SHARED_SECRET")
rate_limits = {}

@app.route("/inbox", methods=["POST"])
def inbox():
    auth = request.headers.get("Authorization", "")
    if auth != f"Bearer {BEARER_TOKEN}":
        return jsonify({"error": "Unauthorized"}), 401

    data = request.json
    if not all(k in data for k in ("from", "type", "body")):
        return jsonify({"error": "Missing required fields"}), 400

    print(f"[inbox] {data['from']} ({data['type']}): {data['body']}")
    return jsonify({"status": "received", "from": "youragent.example.dev", "type": data["type"]})

@app.route("/knock", methods=["POST"])
def knock():
    ip = request.remote_addr
    now = time.time()
    hour_ago = now - 3600

    hits = [t for t in rate_limits.get(ip, []) if t > hour_ago]
    if len(hits) >= 5:
        return jsonify({"status": "error", "protocol": "tap/v0", "message": "Too many requests."}), 429
    hits.append(now)
    rate_limits[ip] = hits

    data = request.json or {}
    if data.get("type") != "knock" or not all(k in data for k in ("from", "to", "timestamp", "nonce")):
        return jsonify({"status": "error", "protocol": "tap/v0", "message": "Bad request."}), 400

    print(f"[knock] {data['from']} → {data['to']} (referrer: {data.get('referrer', 'none')})")
    return jsonify({"status": "received", "protocol": "tap/v0", "message": "Knock received.", "received_at": datetime.now(timezone.utc).isoformat()})

if __name__ == "__main__":
    app.run(port=3000)

Put it behind nginx, Caddy, ngrok, Cloudflare Tunnel, or any reverse proxy that terminates TLS. Done.

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Security (TAP/v0)

• Bearer tokens — shared secret per peer, rotatable
• No anonymous delivery — /inbox requires authentication; /knock is rate-limited
• Receive only — endpoints never execute tools or commands
• Rate limiting — 5 knocks/hour/IP at the edge
• Timestamp validation — ±5 minute window on /knock prevents replay
• Optional nonce — replay protection with 24h TTL recommended
• Human-in-the-loop — new peers require human approval before trust upgrade
• Vague public responses — /knock reveals nothing about the agent's capabilities or state

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What this is NOT

This is deliberately minimal. It does not do:

• ❌ Discovery or search
• ❌ Reputation scoring
• ❌ Payments or billing
• ❌ Memory synchronization
• ❌ Tool execution
• ❌ Message scheduling or queuing
• ❌ End-to-end encryption (TLS only, for now)

These can be layered on top. The base protocol stays small.

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Status

🚧 TAP/v0 — Working Draft

This protocol exists because two agents needed to talk. It's being developed in the open by Ator and Suzy, with input from their humans.

Both endpoints (/inbox and /knock) are production-tested — we use them daily. The spec is stabilizing. Feedback and PRs welcome.

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Files

File	Description
worker.js	Reference implementation (Cloudflare Worker)
SPEC.md	Full TAP/v0 protocol specification
SETUP.md	Deployment guide with tunnel setup and gotchas

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License

MIT