Hermes PayGuard

Hermes PayGuard is a standalone Hermes plugin for safe-by-design USDC and x402 payments.

It does not patch Hermes core. It installs as an add-on and gives Hermes payment tools with an explicit operator boundary:

• Hermes can prepare payment intents.
• Hermes can inspect payment status.
• Hermes can execute only if policy allows it.
• Larger transfers require a separate human approval stamp via payguard approve <intent-id>.
• Tiny x402 micropayments can auto-run below a configured threshold.
• Mainnet is the default profile; testnet is an explicit override.

Documentation

• Install: docs/installation.md
• Operator flow: docs/operator-guide.md
• CCTP executor boundary: docs/cctp-executor.md
• Architecture: docs/architecture.md

What it supports

• Circle developer-controlled USDC transfers
• Circle user-controlled transfer challenges
• Circle CCTP cross-chain USDC route quoting and attestation-aware execution flow
• x402 paid HTTP fetches, including micropayments and nanopayments
• Local audit ledger and replayable intent state

Security model

PayGuard follows the same trust-boundary philosophy as CaMeL Guard, but adapted to payments.

• Trusted control: operator-approved payment intent, local policy, explicit approval stamps
• Untrusted data: webpages, invoices, PDFs, chat text, scraped addresses, model proposals
• Gated execution: payment tools re-check policy and approval state before moving money

The key implementation detail is that approval is external to the model loop. Hermes can stage payment intents, but a separate operator command creates the approval stamp:

payguard approve <intent-id>

That avoids the weakest version of “agent-approved its own payment.”

Install

Repo plugin mode

Clone the repo and symlink it into Hermes' plugin directory:

git clone https://github.com/nativ3ai/hermes-payguard.git
mkdir -p ~/.hermes/plugins
ln -sfn /path/to/hermes-payguard ~/.hermes/plugins/hermes-payguard
pip install -e /path/to/hermes-payguard

Pip plugin mode

pip install hermes-payguard

Quick path:

git clone https://github.com/nativ3ai/hermes-payguard.git
cd hermes-payguard
pip install -e .
payguard install-plugin
payguard init-policy
payguard doctor

Configure

Create ~/.hermes/payguard/policy.yaml:

mode: enforce
network_profile: mainnet
asset: USDC
default_chain: BASE
per_payment_limit_usdc: 100
micro_auto_approve_limit_usdc: 0.05
allowed_circle_recipients:
  - "0x1111111111111111111111111111111111111111"
allowed_cctp_destination_chains: []
allowed_x402_hosts:
  - 127.0.0.1
  - localhost
allow_unlisted_cctp_destinations: true

Then set the relevant env vars.

Profile selection

Mainnet is the default. To force testnet defaults instead:

export PAYGUARD_ENV="testnet"

That switches the default Circle and x402 profiles to:

• default_chain=BASE-SEPOLIA
• CIRCLE_API_BASE_URL=https://api-sandbox.circle.com
• CIRCLE_CCTP_API_BASE_URL=https://iris-api-sandbox.circle.com
• PAYGUARD_X402_NETWORK=eip155:84532

Circle developer-controlled

export CIRCLE_API_KEY="..."
export CIRCLE_ENTITY_SECRET_CIPHERTEXT="..."
export CIRCLE_WALLET_ID="..."
export CIRCLE_TOKEN_ID="..."

Circle user-controlled

export CIRCLE_API_KEY="..."
export CIRCLE_X_USER_TOKEN="..."

Circle CCTP

export CCTP_EXECUTOR_URL="https://your-burn-executor.internal/execute-cctp"

CCTP_EXECUTOR_URL is the boundary between PayGuard and the actual source-chain burn signer. PayGuard handles:

• route fee lookup
• source/destination domain resolution
• intent staging
• approval gating
• message/attestation tracking

The executor is responsible for submitting the actual burn transaction and returning a transactionHash.

x402 buyer

export PAYGUARD_EVM_PRIVATE_KEY="0x..."
export PAYGUARD_X402_NETWORK="eip155:8453"

Operator flow

1. Hermes prepares a transfer with payguard_prepare_usdc_transfer.
2. The tool writes a pending intent into the local ledger.
3. If approval is required, Hermes tells you to run:

payguard approve <intent-id>

4. Hermes then calls payguard_execute_payment_intent.

For tiny x402 payments below the configured threshold, payguard_fetch_paid_url can auto-pay without a separate approval stamp.

Hermes examples

Natural prompts Hermes can handle once the plugin is installed:

Prepare a 12.5 USDC transfer to 0xabc... on Circle developer-controlled wallets for vendor invoice March-20.

Prepare a 50 USDC CCTP transfer from BASE to ARBITRUM for 0xabc..., use standard finality, and stage it for approval.

Fetch the paid x402 URL https://example.com/premium if the micropayment is below policy limits.

Test coverage

Verified locally:

• mainnet profile defaults
• Circle developer-controlled transfer intent -> CLI approval -> execution
• Circle user-controlled transfer intent -> CLI approval -> challenge creation
• CCTP transfer intent -> CLI approval -> executor call -> Circle message/attestation tracking
• x402 micropayment auto-pay flow
• x402 over-limit intent -> CLI approval -> paid fetch
• Hermes plugin discovery and tool registration

Detailed notes:

• docs/architecture.md
• docs/installation.md
• docs/operator-guide.md
• docs/cctp-executor.md

Tool summary

• payguard_prepare_usdc_transfer
• payguard_prepare_cctp_transfer
• payguard_execute_payment_intent
• payguard_get_payment_intent
• payguard_list_payment_intents
• payguard_fetch_paid_url

Tests

pip install -e .[test]
pytest -q

The test suite includes:

• mainnet profile default selection
• Circle developer-controlled mock transfer flow
• Circle user-controlled challenge flow
• CCTP route/attestation flow with local executor and Circle API mocks
• x402 paid fetch flow with auto-approved micropayments
• x402 over-limit flow with explicit operator approval
• Hermes plugin discovery and tool registration