Library for Activating AI Agent Payments Using the Nevermined Protocol

TypeScript SDK to interact with the Nevermined Payments Protocol
nevermined.io

Motivation

The evolution of AI-native commerce is inevitable, but the infrastructure to support it is currently lacking. Today, AI agents require seamless, automated payment systems for individual transactions. As demand grows, these agents will scale into swarms, transacting and operating autonomously.

Existing solutions are designed for human use with physical money. This does not reflect the new reality, where AI Agents need to make and receive payments quickly and efficiently, without the limitations of traditional payment systems.

Nevermined provides a solution that seamlessly evolves from single-agent needs to complex AI economies, eliminating friction and supporting a fully autonomous, composable future for AI-driven commerce.

What is the Nevermined Payments Library?

The Nevermined Payments Library is a TypeScript SDK that allows AI Builders and Subscribers to make AI Agents available for querying and use by other agents or humans. It is designed to be used alongside the Nevermined protocol, which provides a decentralized infrastructure for managing AI agents and their interactions.

The Payments Library enables:

• Easy registration and discovery of AI agents and the payment plans required to access them. All agents registered in Nevermined expose their metadata in a generic way, making them searchable and discoverable for specific purposes.
• Flexible definition of pricing options and how AI agents can be queried. This is achieved through payment plans (based on time or credits) and consumption costs (fixed per request or dynamic). All of this can be defined by the AI builder or agent during the registration process.
• Subscribers (humans or other agents) to purchase credits that grant access to AI agent services. Payments can be made in crypto or fiat via Stripe integration. The protocol registers the payment and credits distribution settlement on-chain.
• Agents or users with access credits to query other AI agents. Nevermined authorizes only users with sufficient balance and keeps track of their credit usage.

The library is designed for use in browser environments or as part of AI Agents:

• In a browser, the library provides a simple way to connect to the Nevermined protocol, allowing users to query AI Agents or publish their own.
• As part of an AI Agent, the library allows the agent to query other agents programmatically. Additionally, agents can use the library to expose their own services and make them available to other agents or humans.

Quickstart

# pnpm
pnpm add @nevermined-io/payments@^1.1

# npm
npm install @nevermined-io/payments@^1.1

Pin the major version (or rely on a committed lockfile) so SDK upgrades are explicit. Always commit package-lock.json / pnpm-lock.yaml.

A2A Integration (Agents‑to‑Agents)

Nevermined Payments integrates with the A2A protocol to authorize and charge per request between agents:

• Discovery: publish the Agent Card at /.well-known/agent.json.
• Streaming and resubscribe: set capabilities.streaming: true for message/stream and tasks/resubscribe.
• Authentication: credentials travel in HTTP headers (payment-signature header per X402 v2 spec), not in the JSON‑RPC payload.
• Authorization/charging: the agent emits a final event with metadata.creditsUsed; Nevermined validates and burns credits accordingly.

Payment extension required in the Agent Card

Add a payment extension under capabilities.extensions carrying Nevermined metadata:

{
  "capabilities": {
    "streaming": true,
    "pushNotifications": true,
    "extensions": [
      {
        "uri": "urn:nevermined:payment",
        "description": "Dynamic cost per request",
        "required": false,
        "params": {
          "paymentType": "dynamic",
          "credits": 1,
          "planId": "<planId>",
          "agentId": "<agentId>"
        }
      }
    ]
  },
  "url": "https://your-agent.example.com/a2a/"
}

Important notes:

• The url must match exactly the URL registered in Nevermined for the agent/plan.
• The final streaming event must include metadata.creditsUsed with the consumed cost.

Requirements

To use the Nevermined Payments Library, you need to get your Nevermined API key. You can get yours freely from the Nevermined App.

Environments

• Available environments: sandbox, live.

Pick the environment that matches where your agent and plans are registered. The agent card url must belong to that environment.

Initialize the Payments library in the Browser

This is a browser only method. Here we have an example using react. For a full example please refer to payments-nextjs-example

import { useEffect } from "react";
import { Payments } from "@nevermined-io/payments";

export default function Home() {
  const payments = Payments.getBrowserInstance({
    returnUrl: "http://localhost:8080",
    environment: "sandbox",
  });

  const onLogin = () => {
    payments.connect();
  };

  return (
    <main>
      <div>
        <button onClick={onLogin}>Login</button>
      </div>
    </main>
  );
}

Initialize the Payments library in an AI Agent

import { Payments } from "@nevermined-io/payments";

const payments = Payments.getInstance({
  nvmApiKey,
  environment: 'sandbox' as EnvironmentName,
})

Create a Payments Plan

Once the app is initialized we can create a payment plan:

const planMetadata: PlanMetadata = {
    name: 'E2E test Payments Plan',
  }
const priceConfig = payments.plans.getERC20PriceConfig(20n, ERC20_ADDRESS, builderAddress)
const creditsConfig = payments.plans.getFixedCreditsConfig(100n)
const { planId } = await payments.plans.registerCreditsPlan(planMetadata, priceConfig, creditsConfig)

Or register a plan limited by time:

const priceConfig = payments.plans.getERC20PriceConfig(50n, ERC20_ADDRESS, builderAddress)
const expirablePlanConfig = payments.plans.getExpirableDurationConfig(payments.plans.ONE_DAY_DURATION) // 1 day
const response = await payments.plans.registerTimePlan(planMetadata, priceConfig, expirablePlanConfig)

You can also create trial plans (free plans that can only be purchased once):

import { ONE_DAY_DURATION } from '@nevermined-io/payments'

// Credits-based trial plan
const trialPlanMetadata = { name: 'Free Trial Plan' }
const freePriceConfig = payments.plans.getFreePriceConfig()
const trialCreditsConfig = payments.plans.getFixedCreditsConfig(10n)

const trialPlan = await payments.plans.registerCreditsTrialPlan(
  trialPlanMetadata,
  freePriceConfig,
  trialCreditsConfig
)

// Time-based trial plan
const timeTrialConfig = payments.plans.getExpirableDurationConfig(ONE_DAY_DURATION)
const timeTrialPlan = await payments.plans.registerTimeTrialPlan(
  trialPlanMetadata,
  freePriceConfig,
  timeTrialConfig
)

Create an AI Agent/Service

You can register an agent with existing payment plans:

// Some metadata about the agent
const agentMetadata = {
  name: 'E2E Payments Agent',
  tags: ['test'],
}

// The API that the agent will expose
const agentApi = {
  endpoints: [
    { 'POST': `https://example.com/api/v1/agents/:agentId/tasks` },
    { 'GET': `https://example.com/api/v1/agents/:agentId/tasks/invoke` }
]}

// This is the list of payment plans that the agent will accept
const paymentPlans = [ creditsPlanId, expirablePlanId ]
const result = await payments.agents.registerAgent(agentMetadata, agentApi, paymentPlans)

Or register an agent and plan together in one step:

import { ONE_DAY_DURATION } from '@nevermined-io/payments'

const agentMetadata = {
  name: 'My AI Payments Agent',
  tags: ['ai', 'assistant'],
}

const agentApi = {
  endpoints: [
    { 'POST': 'https://example.com/api/v1/agents/:agentId/tasks' }
  ]
}

const planMetadata = { name: 'Basic Plan' }
const priceConfig = payments.plans.getERC20PriceConfig(20n, ERC20_ADDRESS, builderAddress)
const creditsConfig = payments.plans.getExpirableDurationConfig(ONE_DAY_DURATION)

// Register agent and plan together
const { agentId, planId, txHash } = await payments.agents.registerAgentAndPlan(
  agentMetadata,
  agentApi,
  planMetadata,
  priceConfig,
  creditsConfig,
  'time' // Optionally set access limit to 'time' or 'credits'
)

The accessLimit parameter is optional. If not specified, it's automatically inferred:

• 'credits' if creditsConfig.durationSecs === 0n (non-expirable)
• 'time' if creditsConfig.durationSecs > 0n (expirable)

Purchase a Payment Plan

const orderResult = await payments.plans.orderPlan(creditsPlanId)

And get the balance of the purchased plan:

const balance = await payments.plans.getPlanBalance(creditsPlanId)
console.log(`Balance: ${balance}`)

Query an AI Agent

Once the user has purchased a plan, they can query the agent:

const { accessToken } = await payments.x402.getX402AccessToken(creditsPlanId, agentId)

const agentHTTPOptions = {
  method: 'POST',
  headers: {
    Accept: 'application/json',
    'Content-Type': 'application/json',
    'payment-signature': accessToken
  },
}
const response = await fetch(new URL(agentURL), agentHTTPOptions)

MCP (Model Context Protocol)

What is MCP?

The Model Context Protocol (MCP) is a standardized communication layer for AI. It allows agents to discover and use server capabilities through:

• Tools: Actions the agent can execute (e.g., fetch weather data)
• Resources: Stable data pointers identified by URI (e.g., JSON weather data)
• Prompts: Pre-defined templates guiding agent behavior

MCP servers expose handlers (tools/resources/prompts) with their logical URLs, such as mcp://mcp-server/tools/my-tooling. Clients send requests with Authorization: Bearer <token>, protected by Nevermined Payments Engine and receive JSON‑RPC results or errors.

Why Nevermined Payments?

While MCP defines what an agent can do, it doesn't specify who can access it or how to charge for it. Nevermined Payments adds:

• Authentication: Validates user tokens via Authorization header
• Credit System: Checks and deducts credits per request
• Automatic Setup: Handles Express, sessions, OAuth endpoints

How It Works

1. Initialize Nevermined Payments

import { Payments, EnvironmentName } from "@nevermined-io/payments";

const payments = Payments.getInstance({
  nvmApiKey: process.env.NVM_API_KEY!,
  environment: process.env.NVM_ENVIRONMENT! as EnvironmentName,
});

2. Register Protected Tools

import { z } from "zod";

const schema = z.object({
  city: z.string().describe("City name"),
}) as any;

payments.mcp.registerTool(
  "weather.today",
  {
    title: "Today's Weather",
    description: "Get weather for a city",
    inputSchema: schema,
  },
  async (args) => {
    const { city } = args as { city: string };
    return {
      content: [{ type: "text", text: `Weather for ${city}: Sunny, 25C` }],
    };
  },
  { credits: 1n }
);

3. Register Protected Resources

payments.mcp.registerResource(
  "Weather Data",
  "weather://today",
  {
    title: "Today's Weather",
    description: "JSON weather data",
    mimeType: "application/json",
  },
  async (uri) => {
    return {
      contents: [{ uri: uri.href, text: "{...}", mimeType: "application/json" }],
    };
  },
  { credits: 5n }
);

4. Register Protected Prompts

payments.mcp.registerPrompt(
  "weather.ensureCity",
  {
    title: "Ensure city",
    description: "Guide to call weather.today",
    argsSchema: schema,
  },
  (args) => {
    return {
      messages: [{ role: "user", content: { type: "text", text: "..." } }],
    };
  },
  { credits: (ctx) => ctx.result.length > 100 ? 2n : 1n }  // Dynamic credits
);

5. Start the Server

const { info, stop } = await payments.mcp.start({
  port: 3002,
  agentId: process.env.NVM_AGENT_ID!,
  serverName: "weather-mcp",
  version: "0.1.0",
});

Credit Configuration

All registration functions support fixed or dynamic credits:

// Fixed credits
{ credits: 1n }
{ credits: 5n }

// Dynamic credits based on input
{ credits: (ctx) => ctx.args.premium ? 5n : 1n }

// Dynamic credits based on result
{ credits: (ctx) => ctx.result.length > 1000 ? 3n : 1n }

// Tiered pricing
{ credits: (ctx) => {
  const size = JSON.stringify(ctx.result).length;
  if (size > 1000) return 5n;
  if (size > 500) return 3n;
  return 1n;
}}

Client Usage

Get Access Token

import { Payments } from "@nevermined-io/payments";

const payments = Payments.getInstance({
  nvmApiKey: process.env.NVM_API_KEY!,
  environment: "sandbox",
});

const { accessToken } = await payments.x402.getX402AccessToken(
  process.env.NVM_PLAN_ID!,
  process.env.NVM_AGENT_ID!
);

Call Protected Tools

import { Client } from "@modelcontextprotocol/sdk/client";
import { StreamableHTTPClientTransport } from "@modelcontextprotocol/sdk/client/streamableHttp";

const transport = new StreamableHTTPClientTransport(
  new URL("http://localhost:3002/mcp"),
  { requestInit: { headers: { Authorization: `Bearer ${accessToken}` } } }
);

const client = new Client({ name: "my-client" });
await client.connect(transport);

const result = await client.callTool({
  name: "weather.today",
  arguments: { city: "London" },
});

Endpoints

Endpoint	Description
POST /mcp	MCP JSON-RPC requests
GET /mcp	SSE stream for notifications
DELETE /mcp	Session termination
GET /health	Health check
GET /	Server info

Error Codes

Code	Description
-32003	Authorization required / Payment required / Insufficient credits
-32002	Server error

Notes

• The wrapper reads Authorization header, authenticates the x402 token via authenticator.authenticate(), executes the handler, and redeems credits via facilitator.settlePermissions() using x402 PaymentRequired.
• credits can be a bigint or (ctx) => bigint with { args, result }. Use args for input-based pricing and result for output-based pricing.
• name builds the logical URL mcp://{serverName}/{kind}/{name}.

Documentation

Comprehensive markdown documentation is available in the markdown/ directory:

• Installation - Setup and prerequisites
• Initialization - Getting started with the SDK
• Payment Plans - Creating and managing payment plans
• Agents - Registering and managing AI agents
• Static Resources - Publishing static content
• Payments & Balance - Ordering plans and checking balances
• Querying Agents - Using X402 access tokens
• Request Validation - Verifying and settling permissions
• MCP Integration - Model Context Protocol setup
• A2A Integration - Agent-to-Agent protocol setup
• X402 Protocol - Complete payment protocol specification

Automated Documentation

The documentation is automatically maintained and published:

• On Push: Documentation metadata is updated when source code changes
• On Tag: Documentation is published to nevermined-io/docs_mintlify repository

For more details, see DOCUMENTATION.md.

Quick Commands

# Validate documentation
./scripts/generate-docs.sh

# Publish documentation (manual)
./scripts/publish-docs.sh

# View workflows
gh run list --workflow=update-docs.yml
gh run list --workflow=publish-docs.yml

License

Copyright 2025 Nevermined AG

Licensed under the Apache License, Version 2.0 (the "License");
you may not use this file except in compliance with the License.
You may obtain a copy of the License at

   http://www.apache.org/licenses/LICENSE-2.0

Unless required by applicable law or agreed to in writing, software
distributed under the License is distributed on an "AS IS" BASIS,
WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
See the License for the specific language governing permissions and
limitations under the License.