PUBSUB: publish a message to a topic YOU own, fanning out a signed callback to every CONFIRMED subscriber. Returns the number of subscribers it was delivered to. Only the topic owner (the x402 payer who created it) can publish. Message is arbitrary JSON (≤64 KB). Priced by confirmed-subscriber count (a small base + per subscriber), so you pay for the fan-out you request. Delivery is at-least-once with retry + signature.
/api/pubsub/publishPAYMENT-SIGNATURE.The publish API is a pay-per-call pubsub endpoint built for AI agents and autonomous software. PUBSUB: publish a message to a topic YOU own, fanning out a signed callback to every CONFIRMED subscriber.
There is no signup and no API key. An agent (or any HTTP client) hits the endpoint, receives an x402 "402 Payment Required" challenge, signs a sub-cent USDC payment on Base or Solana, and retries — the data comes back on the paid request. That makes it a drop-in publish data source for an agent tool-use loop, an MCP host, or a backend that needs pubsub data on demand without onboarding to yet another vendor portal.
| Name | Type | Description |
|---|---|---|
topicIdrequired | string | The topic you own (from pubsub.create-topic). |
message | The payload to fan out — any JSON, up to 64 KB. |
# 1. Probe the endpoint with no auth — receive 402 with PaymentRequirements
curl -sS -X POST 'https://2s.io/api/pubsub/publish' \
-H 'Content-Type: application/json' \
-d '{"topicId":"example"}'
# 2. Sign the EIP-3009 transferWithAuthorization for the advertised price +
# payTo from the 402 envelope, then retry with PAYMENT-SIGNATURE:
curl -sS -X POST 'https://2s.io/api/pubsub/publish' \
-H 'Content-Type: application/json' \
-H 'PAYMENT-SIGNATURE: <base64-json-payload>' \
-d '{"topicId":"example"}'
# Or just use the canonical runner — it handles the whole loop:
# EVM_PRIVATE_KEY=0x... node --env-file=.env.local \
# --experimental-strip-types scripts/x402-pay.ts \
# 'https://2s.io/api/pubsub/publish'import { TwoS } from '@2sio/sdk'
const client = new TwoS({
privateKey: process.env.EVM_PRIVATE_KEY as `0x${string}`,
})
const result = await client.pubsub.publish({
"topicId": "example"
})
console.log('endpoint:', result.endpoint)
console.log('cost:', result.costUsd, 'USDC')
console.log('tx:', result.settlement?.txHash)
console.log('data:', result.data)import os
from twosio import TwoS
client = TwoS(private_key=os.environ["EVM_PRIVATE_KEY"])
result = client.pubsub.publish(topicId="example")
print("endpoint:", result.endpoint)
print("cost:", result.cost_usd, "USDC")
print("tx:", (result.settlement or {}).get("tx_hash"))
print("data:", result.data)// 1. Add @2sio/mcp to your MCP host config (Claude Desktop example below).
// EVM_PRIVATE_KEY funds x402 payments per call.
// claude_desktop_config.json
{
"mcpServers": {
"2sio": {
"command": "npx",
"args": ["-y", "@2sio/mcp"],
"env": { "EVM_PRIVATE_KEY": "0x..." }
}
}
}
// 2. Once the server is running, agents call this tool via standard MCP:
{
"jsonrpc": "2.0",
"id": 1,
"method": "tools/call",
"params": {
"name": "pubsub.publish",
"arguments": {
"topicId": "example"
}
}
}| Field | Type | Description |
|---|---|---|
ok | boolean | one of: true |
items | array | |
total | integer | Total matching rows upstream; null when unknown. |
source | object |
{
"ok": true,
"items": [
{
"topicId": "example",
"delivered": 1
}
],
"total": 1,
"source": {
"provider": "example",
"url": "example",
"license": "example"
}
}