Strands

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Add payment protection to your Strands AI agent tools using the x402 protocol. The @requires_payment decorator handles verification and settlement automatically.

x402 Payment Flow

How Payment Errors Flow

The @requires_payment decorator follows the x402 MCP transport spec — payment errors are returned as tool results with status: "error", not raised as exceptions. Each error includes:

A human-readable text block explaining the payment requirement
A structured JSON block containing the full PaymentRequired object

In Strands, tool errors flow through the LLM. The LLM sees the error and relays it to the user in natural language (e.g., “I need a payment token to use this tool”). The structured PaymentRequired data is preserved in agent.messages. Clients use extract_payment_required(agent.messages) to get the structured PaymentRequired dict from the conversation history. The PaymentRequired contains the accepts array with plan IDs, schemes, and networks needed to acquire an x402 access token.

Installation

pip install payments-py[strands] strands-agents

The [strands] extra installs the Strands SDK dependency required for the decorator.

Quick Start: Protecting a Tool

The @requires_payment decorator wraps a Strands @tool function with x402 payment verification and settlement.

You must use @tool(context=True) instead of plain @tool. This tells Strands to inject tool_context into the function, which the decorator needs to access invocation_state for the payment token.

import os
from dotenv import load_dotenv
from strands import Agent, tool
from payments_py import Payments, PaymentOptions
from payments_py.x402.strands import requires_payment

load_dotenv()

# Initialize Payments
payments = Payments.get_instance(
    PaymentOptions(
        nvm_api_key=os.environ["NVM_API_KEY"],
        environment=os.environ.get("NVM_ENVIRONMENT", "sandbox"),
    )
)

PLAN_ID = os.environ["NVM_PLAN_ID"]

# Protect a tool with payment
@tool(context=True)
@requires_payment(payments=payments, plan_id=PLAN_ID, credits=1)
def analyze_data(query: str, tool_context=None) -> dict:
    """Analyze data based on a query. Costs 1 credit per request.

    Args:
        query: The data analysis query to process.
    """
    return {
        "status": "success",
        "content": [{"text": f"Analysis complete for: {query}"}],
    }

# Create agent with payment-protected tools
agent = Agent(tools=[analyze_data])

That’s it! The decorator automatically:

Returns a PaymentRequired error when no token is provided
Verifies the x402 token via the Nevermined facilitator
Executes the tool function on successful verification
Burns credits after successful execution

Client-Side: Payment Discovery

Clients discover payment requirements by calling the agent without a token, then extracting the PaymentRequired from the conversation history:

from payments_py import Payments, PaymentOptions
from payments_py.x402 import X402TokenOptions, DelegationConfig, CreateDelegationPayload
from payments_py.x402.strands import extract_payment_required
from agent import agent, payments

# Step 1: Call agent without token — triggers PaymentRequired
result = agent("Analyze the latest sales trends")

# Step 2: Extract PaymentRequired from conversation history
payment_required = extract_payment_required(agent.messages)

if payment_required:
    # Step 3: Choose a plan and acquire token
    chosen_plan = payment_required["accepts"][0]
    plan_id = chosen_plan["planId"]
    agent_id = (chosen_plan.get("extra") or {}).get("agentId")

    # Create a delegation once, then reuse its id to mint tokens.
    delegation = payments.delegation.create_delegation(
        CreateDelegationPayload(
            provider="erc4337",  # "stripe" | "braintree" | "visa" for fiat plans
            spending_limit_cents=10000,  # $100 budget
            duration_secs=604800,  # 7 days
            currency="usdc",  # "usd" for fiat plans
        )
    )
    token_response = payments.x402.get_x402_access_token(
        plan_id=plan_id,
        agent_id=agent_id,
        token_options=X402TokenOptions(
            scheme="nvm:erc4337",  # "nvm:card-delegation" for fiat plans
            delegation_config=DelegationConfig(delegation_id=delegation.delegation_id)
        ),
    )
    access_token = token_response["accessToken"]

    # Step 4: Call agent with payment token
    state = {"payment_token": access_token}
    result = agent("Analyze the latest sales trends", invocation_state=state)
    print(f"Result: {result}")

    # Step 5: Check settlement (stored in invocation_state after successful execution)
    settlement = state.get("payment_settlement")
    if settlement:
        print(f"Credits redeemed: {settlement.credits_redeemed}")

Decorator Configuration

The decorator automatically detects the payment scheme from plan metadata. Plans with fiat pricing (isCrypto: false) use nvm:card-delegation (Stripe). No code changes are needed on the agent side. You can explicitly override with the scheme parameter.

Single Plan

@tool(context=True)
@requires_payment(payments=payments, plan_id="plan-123", credits=1)
def my_tool(query: str, tool_context=None) -> dict:
    ...

Multiple Plans

Accept multiple payment plans (e.g., basic and premium tiers):

@tool(context=True)
@requires_payment(
    payments=payments,
    plan_ids=["plan-basic", "plan-premium"],
    credits=1,
)
def my_tool(query: str, tool_context=None) -> dict:
    ...

Dynamic Credits

Calculate credits based on tool arguments:

def calc_credits(kwargs):
    """Charge based on complexity."""
    return kwargs.get("complexity", 1) * 2

@tool(context=True)
@requires_payment(payments=payments, plan_id=PLAN_ID, credits=calc_credits)
def my_tool(query: str, complexity: int = 1, tool_context=None) -> dict:
    ...

With Agent ID

@tool(context=True)
@requires_payment(
    payments=payments,
    plan_id=PLAN_ID,
    credits=1,
    agent_id=os.environ.get("NVM_AGENT_ID"),  # Required for plans with multiple agents
)
def my_tool(query: str, tool_context=None) -> dict:
    ...

Scheme and Network

# Custom network for crypto payments
@tool(context=True)
@requires_payment(
    payments=payments,
    plan_id=PLAN_ID,
    credits=1,
    network="eip155:1",  # Ethereum mainnet (default: eip155:84532 Base Sepolia)
)
def my_crypto_tool(query: str, tool_context=None) -> dict:
    ...

# Explicit card-delegation scheme for fiat payments
@tool(context=True)
@requires_payment(
    payments=payments,
    plan_id=PLAN_ID,
    credits=1,
    scheme="nvm:card-delegation",  # Fiat/Stripe (network auto-set to "stripe")
)
def my_fiat_tool(query: str, tool_context=None) -> dict:
    ...

Lifecycle Hooks

def on_before_verify(payment_required):
    print(f"Verifying payment for {len(payment_required.accepts)} plans")

def on_after_verify(verification):
    print(f"Verified! Request ID: {verification.agent_request_id}")

def on_after_settle(credits_used, settlement):
    print(f"Settled {credits_used} credits")

def on_payment_error(error):
    # Return custom error dict or None for default x402 error
    return None

@tool(context=True)
@requires_payment(
    payments=payments,
    plan_id=PLAN_ID,
    credits=1,
    on_before_verify=on_before_verify,
    on_after_verify=on_after_verify,
    on_after_settle=on_after_settle,
    on_payment_error=on_payment_error,
)
def my_tool(query: str, tool_context=None) -> dict:
    ...

Accessing Payment Context

After verification, the PaymentContext is available in tool_context.invocation_state["payment_context"]:

from payments_py.x402.strands import PaymentContext

@tool(context=True)
@requires_payment(payments=payments, plan_id=PLAN_ID, credits=1)
def my_tool(query: str, tool_context=None) -> dict:
    """Tool with payment context access."""
    ctx = tool_context.invocation_state.get("payment_context")
    if ctx and isinstance(ctx, PaymentContext):
        print(f"Token: {ctx.token}")
        print(f"Credits: {ctx.credits_to_settle}")
        print(f"Request ID: {ctx.agent_request_id}")
        print(f"Verified: {ctx.verified}")

    return {"status": "success", "content": [{"text": "Done"}]}

Complete Example

See the complete working example in the strands-simple-agent directory on GitHub. It includes:

agent.py — Agent with payment-protected tools
demo.py — Full payment discovery and token acquisition flow

Environment Variables

# Nevermined (required)
NVM_API_KEY=sandbox:your-api-key
NVM_ENVIRONMENT=sandbox
NVM_PLAN_ID=your-plan-id
NVM_AGENT_ID=your-agent-id          # Optional

# LLM Provider
OPENAI_API_KEY=sk-your-openai-key   # Or configure your preferred model provider

Next Steps

Payment Patterns

Advanced credit charging patterns

x402 Protocol

Deep dive into x402 payment flows

Payment Models

Configure credits, subscriptions, and dynamic pricing

strands-simple-agent

Complete working example on GitHub

Learn

Build

Payments

Solutions

Integrations

Payment Patterns

Components

Specs

x402 Payment Flow

How Payment Errors Flow

Installation

Quick Start: Protecting a Tool

Client-Side: Payment Discovery

Decorator Configuration

Single Plan

Multiple Plans

Dynamic Credits

With Agent ID

Scheme and Network

Lifecycle Hooks

Accessing Payment Context

Complete Example

Environment Variables

Next Steps

Payment Patterns

x402 Protocol

Payment Models

strands-simple-agent

​x402 Payment Flow

​How Payment Errors Flow

​Installation

​Quick Start: Protecting a Tool

​Client-Side: Payment Discovery

​Decorator Configuration

​Single Plan

​Multiple Plans

​Dynamic Credits

​With Agent ID

​Scheme and Network

​Lifecycle Hooks

​Accessing Payment Context

​Complete Example

​Environment Variables

​Next Steps

Payment Patterns

x402 Protocol

Payment Models

strands-simple-agent

x402 Payment Flow

How Payment Errors Flow

Installation

Quick Start: Protecting a Tool

Client-Side: Payment Discovery

Decorator Configuration

Single Plan

Multiple Plans

Dynamic Credits

With Agent ID

Scheme and Network

Lifecycle Hooks

Accessing Payment Context

Complete Example

Environment Variables

Next Steps