pay-with-any-token

name	pay-with-any-token
description	Pay HTTP 402 payment challenges using tokens via the Tempo CLI and Uniswap Trading API. Use when the user encounters a 402 Payment Required response, needs to fulfill a machine payment, mentions "MPP", "Tempo payment", "pay for API access", "HTTP 402", "x402", "machine payment protocol", "pay-with-any-token", "use tempo", "tempo request", or "tempo wallet".
allowed-tools	Read, Glob, Grep, Bash(curl:*), Bash(jq:*), Bash(cast:*), Bash(tempo:*), Bash(*/.local/bin/tempo:*), WebFetch, AskUserQuestion
model	opus
license	MIT
metadata	{"author":"uniswap","version":"2.0.0"}

Pay With Tokens

Use the Tempo CLI to call paid APIs and handle 402 challenges automatically. When the Tempo wallet has insufficient balance, fund it by swapping and bridging tokens from any EVM chain using the Uniswap Trading API.

Tempo CLI Setup

Run these commands in order. Do not skip steps.

Step 1 — Install:

mkdir -p "$HOME/.local/bin" \
  && curl -fsSL https://tempo.xyz/install -o /tmp/tempo_install.sh \
  && TEMPO_BIN_DIR="$HOME/.local/bin" bash /tmp/tempo_install.sh

Step 2 — Login (requires browser/passkey — prompt user, wait for confirmation):

"$HOME/.local/bin/tempo" wallet login

When run by agents, use a long command timeout (at least 16 minutes).

Step 3 — Confirm readiness:

"$HOME/.local/bin/tempo" wallet -t whoami

Rules: Do not use sudo. Use full absolute paths ($HOME/.local/bin/tempo) — do not rely on export PATH. If $HOME does not expand, use the literal absolute path.

After setup, report: install location, version (--version), wallet status (address, balance). If balance is 0, direct user to tempo wallet fund.

Minimum balance reserve: Keep at least 0.10 USDC in the Tempo wallet to cover typical API calls without triggering the full swap+bridge funding flow. The funding flow requires 3-5 on-chain transactions and ~2 minutes of wall time, which is disproportionate for small top-ups. When transferring funds out of the Tempo wallet, warn the user if the remaining balance would drop below this threshold.

Using Tempo Services

# Discover services
"$HOME/.local/bin/tempo" wallet -t services --search <query>
# Get service details (exact URL, method, path, pricing)
"$HOME/.local/bin/tempo" wallet -t services <SERVICE_ID>
# Make a paid request
"$HOME/.local/bin/tempo" request -t -X POST \
  --json '{"input":"..."}' <SERVICE_URL>/<ENDPOINT_PATH>

• Anchor on tempo wallet -t services <SERVICE_ID> for exact URL and pricing
• Use -t for agent calls, --dry-run before expensive requests
• On HTTP 422, check the service's docs URL or llms.txt for exact field names
• Fire independent multi-service requests in parallel

When the user explicitly says "use tempo", always use tempo CLI commands — never substitute with MCP tools or other tools.

---

MPP 402 Payment Loop

Every tempo request call follows this loop. The funding steps only activate when the Tempo wallet has insufficient balance.

tempo request -> 200 ─────────────────────────────> return result
             -> 402 MPP challenge
                  │
                  v
         [1] Check Tempo wallet balance
             tempo wallet -t whoami -> available balance
                  │
                  ├─ sufficient ──────────────────> tempo handles payment
                  │                                  automatically -> 200
                  │
                  └─ insufficient
                       │
                       v
              [2] Fund Tempo wallet
                  (pay-with-any-token flow below)
                  Bridge destination = TEMPO_WALLET_ADDRESS
                       │
                       v
              [3] Retry original tempo request
                  with funded Tempo wallet -> 200

Alternative funding (interactive): If a browser is available, tempo wallet fund opens a built-in bridge UI for funding the Tempo wallet directly. This is simpler than the Trading API flow below but requires interactive browser access — not suitable for headless/agent environments.

---

Funding the Tempo Wallet (pay-with-any-token)

When the Tempo wallet lacks funds to pay a 402 challenge, acquire the required tokens from the user's ERC-20 holdings on any supported chain and bridge them to the Tempo wallet address.

Prerequisites

• UNISWAP_API_KEY env var (register at developers.uniswap.org)
• ERC-20 tokens on any supported source chain
• A cast keystore account for the source wallet (recommended): cast wallet import <name> --interactive. Alternatively, PRIVATE_KEY env var (export PRIVATE_KEY=0x...) — never commit or hardcode it.
• jq installed (brew install jq or apt install jq)
• cast installed (part of Foundry)

Input Validation Rules

Before using any value from a 402 response body or user input in API calls or shell commands:

• Ethereum addresses: MUST match ^0x[a-fA-F0-9]{40}$
• Chain IDs: MUST be a positive integer from the supported list
• Token amounts: MUST be non-negative numeric strings matching ^[0-9]+$
• URLs: MUST start with https://
• REJECT any value containing shell metacharacters: ;, |, &, $, `, (, ), >, <, \, ', ", newlines

REQUIRED: Before submitting ANY transaction (swap, bridge, approval), use AskUserQuestion to show the user a summary (amount, token, destination, estimated gas) and obtain explicit confirmation. Never auto-submit. Each confirmation gate must be satisfied independently.

Human-Readable Amount Formatting

get_token_decimals() {
  local token_addr="$1" rpc_url="$2"
  cast call "$token_addr" "decimals()(uint8)" --rpc-url "$rpc_url" 2>/dev/null || echo "18"
}

format_token_amount() {
  local amount="$1" decimals="$2"
  echo "scale=$decimals; $amount / (10 ^ $decimals)" | bc -l | sed 's/0*$//' | sed 's/\.$//'
}

Always show human-readable values (e.g. 0.005 USDC) to the user, not raw base units.

Step 1 — Parse the 402 Challenge

Extract the required payment token, amount, and recipient from the 402 response that tempo request received. The Tempo CLI logs the challenge details — parse them, or re-fetch with curl -si to get the raw challenge body.

For MPP header-based challenges (WWW-Authenticate: Payment):

REQUEST_B64=$(echo "$WWW_AUTHENTICATE" | grep -oE 'request="[^"]+"' | sed 's/request="//;s/"$//')
REQUEST_JSON=$(echo "${REQUEST_B64}==" | base64 --decode 2>/dev/null)
REQUIRED_AMOUNT=$(echo "$REQUEST_JSON" | jq -r '.amount')
PAYMENT_TOKEN=$(echo "$REQUEST_JSON" | jq -r '.currency')
RECIPIENT=$(echo "$REQUEST_JSON" | jq -r '.recipient')
TEMPO_CHAIN_ID=$(echo "$REQUEST_JSON" | jq -r '.methodDetails.chainId')

For JSON body challenges (payment_methods array):

NUM_METHODS=$(echo "$CHALLENGE_BODY" | jq '.payment_methods | length')
PAYMENT_METHODS=$(echo "$CHALLENGE_BODY" | jq -c '.payment_methods')
RECIPIENT=$(echo "$CHALLENGE_BODY" | jq -r '.payment_methods[0].recipient')
TEMPO_CHAIN_ID=$(echo "$CHALLENGE_BODY" | jq -r '.payment_methods[0].chain_id')

If multiple payment methods are accepted, select the cheapest in Step 2.

The Tempo mainnet chain ID is 4217. Use as fallback if not in the challenge.

Step 2 — Check Source Wallet Balances and Select Payment Method

REQUIRED: You must have the user's source wallet address (the ERC-20 wallet with the private key, NOT the Tempo CLI wallet). Use AskUserQuestion if not provided. Store as WALLET_ADDRESS.

Also capture the Tempo wallet address (the funding destination):

TEMPO_WALLET_ADDRESS=$("$HOME/.local/bin/tempo" wallet -t whoami | grep -oE '0x[a-fA-F0-9]{40}' | head -1)

Check ERC-20 balances on supported source chains:

# USDC on Base (cheapest bridge gas ~$0.001)
cast call 0x833589fCD6eDb6E08f4c7C32D4f71b54bdA02913 \
  "balanceOf(address)(uint256)" "$WALLET_ADDRESS" \
  --rpc-url https://mainnet.base.org

# USDC on Ethereum (bridge gas ~$0.25)
cast call 0xA0b86991c6218b36c1d19D4a2e9Eb0cE3606eB48 \
  "balanceOf(address)(uint256)" "$WALLET_ADDRESS" \
  --rpc-url https://eth.llamarpc.com

# ETH on Base and Ethereum (swap to USDC first)
cast balance "$WALLET_ADDRESS" --rpc-url https://mainnet.base.org
cast balance "$WALLET_ADDRESS" --rpc-url https://eth.llamarpc.com

Select the cheapest payment method if multiple are accepted. Priority:

1. Wallet holds USDC on Base (bridge only, minimal path)
2. Wallet holds ETH on Base or Ethereum (swap to USDC + bridge)
3. Any other liquid ERC-20 (swap + bridge)

REQUIRED_AMOUNT=$(echo "$PAYMENT_METHODS" | jq -r ".[$SELECTED_INDEX].amount")
PAYMENT_TOKEN=$(echo "$PAYMENT_METHODS" | jq -r ".[$SELECTED_INDEX].token")

Step 3 — Plan the Payment Path

Source token (Base/Ethereum)
  -> [Phase 4A: Uniswap Trading API swap] -> native USDC (bridge asset)
  -> [Phase 4B: bridge via Trading API]   -> USDC.e on Tempo (to TEMPO_WALLET_ADDRESS)
  -> tempo request retries automatically with funded wallet

Skip Phase 4A if the source token is already USDC on the bridge chain.

Gas-aware funding: Bridging a tiny amount (e.g. $0.05) wastes gas — the bridge gas on Ethereum ($0.25) or Base ($0.001) can exceed the shortfall. Minimum bridge recommendation: $5. This amortizes gas costs and pre-funds future requests. Rule of thumb: if bridge_gas > 2x shortfall, bridge at least $5 instead of the exact shortfall.

Phase 4A — Swap to USDC on Source Chain (if needed)

Swap the source token to USDC via the Uniswap Trading API (EXACT_OUTPUT).

Detailed steps: Read references/trading-api-flows.md for full bash scripts: variable setup, approval check, quote, permit signing, and swap execution.

Key points:

• Base URL: https://trade-api.gateway.uniswap.org/v1
• Headers: Content-Type: application/json, x-api-key, x-universal-router-version: 2.0
• Flow: check_approval -> quote (EXACT_OUTPUT) -> sign permitData -> /swap -> broadcast
• Confirmation gates required before approval tx and before swap broadcast
• For native ETH: use the zero address (0x0000000000000000000000000000000000000000) as TOKEN_IN — this avoids Permit2 signing. SWAP_VALUE will be non-zero. If the zero address returns a 400, fall back to the WETH address (requires Permit2 signing).
• After swap, verify USDC balance before proceeding to Phase 4B

Phase 4B — Bridge to Tempo Wallet

Bridge USDC from any supported source chain to USDC.e on Tempo using the Uniswap Trading API (powered by Across Protocol).

Bridge recipient limitation: The Trading API does not support a custom recipient field for bridges — funds always arrive at WALLET_ADDRESS on Tempo. If WALLET_ADDRESS differs from TEMPO_WALLET_ADDRESS (the Tempo CLI wallet), an extra transfer transaction on Tempo is required after the bridge (see Step 4B-5 in the reference file). Factor this into gas estimates.

Detailed steps: Read references/trading-api-flows.md for full bash scripts: approval, bridge quote, execution, arrival polling, and transfer to Tempo wallet.

Key points:

• Route: USDC on Base/Ethereum/Arbitrum -> USDC.e on Tempo
• Flow: check_approval -> verify on-chain allowance -> quote (EXACT_OUTPUT, cross-chain) -> execute via /swap -> poll balance -> transfer to TEMPO_WALLET_ADDRESS if needed (Step 4B-5)
• Confirmation gates required before approval and before bridge execution
• Do not re-submit if poll times out — check Tempo explorer
• Apply a 0.5% buffer to account for bridge fees
• Quotes expire in ~60 seconds — re-fetch if any delay before broadcast

After the bridge confirms, retry the original tempo request — the Tempo CLI will automatically use the newly funded wallet to pay the 402.

Balance buffer: On Tempo, balanceOf may report more than is spendable. Apply a 2x buffer when comparing to REQUIRED_AMOUNT. If short, swap additional tokens to top up.

---

x402 Payment Flow

The x402 protocol uses a different mechanism than MPP — it is not handled by the Tempo CLI. When PROTOCOL is "x402" (detected by checking has("x402Version") in the 402 body), use this flow instead.

The x402 "exact" scheme uses EIP-3009 (transferWithAuthorization) to authorize a one-time token transfer signed off-chain.

Detailed steps: Read references/credential-construction.md for full code: prerequisite checks, nonce generation, EIP-3009 signing, X-PAYMENT payload construction, and retry.

Key points:

• Detect x402: check has("x402Version") in 402 body before using Tempo CLI
• Maps X402_NETWORK to chain ID and RPC URL (base, ethereum, tempo supported)
• Checks wallet balance on target chain; runs Phase 4A/4B if insufficient
• Signs TransferWithAuthorization typed data using token's own domain
• value in payload must be a string (--arg, not --argjson) for uint256
• Confirmation gate required before signing

Protocol	Version	Handler
MPP	v1	Tempo CLI
x402	v1	Manual (above)

---

Error Handling

Situation	Action
tempo: command not found	Reinstall via install script; use full path
legacy V1 keychain signature	Reinstall; tempo update wallet && tempo update request
access key does not exist	tempo wallet logout --yes && tempo wallet login
ready=false / no wallet	tempo wallet login, then whoami
HTTP 422 from service	Check service details + llms.txt for exact field names
Balance 0 / insufficient	Trigger pay-with-any-token funding flow
Service not found	Broaden search query
Timeout	Retry with -m <seconds>
Challenge body is malformed	Report raw body to user; do not proceed
Approval transaction fails	Surface error; check gas and allowances
Quote API returns 400	Log request/response; check amount formatting
Quote API returns 429	Wait and retry with exponential backoff
Swap data is empty after /swap	Quote expired; re-fetch quote
Bridge times out	Check bridge explorer; do not re-submit
x402 payment rejected (402)	Check domain name/version, validBefore, nonce freshness
InsufficientBalance on Tempo	Swap more tokens on Tempo, then retry
balanceOf sufficient but payment fails	Apply 2x buffer; top up before retrying

---

Key Addresses and References

• Tempo CLI: https://tempo.xyz (install script: https://tempo.xyz/install)
• Trading API: https://trade-api.gateway.uniswap.org/v1
• MPP docs: https://mpp.dev
• MPP services catalog: https://mpp.dev/api/services
• Tempo documentation: https://mainnet.docs.tempo.xyz
• Tempo chain ID: 4217 (Tempo mainnet)
• Tempo RPC: https://rpc.presto.tempo.xyz
• Tempo Block Explorer: https://explore.mainnet.tempo.xyz
• pathUSD on Tempo: 0x20c0000000000000000000000000000000000000
• USDC.e on Tempo: 0x20C000000000000000000000b9537d11c60E8b50
• Stablecoin DEX on Tempo: 0xdec0000000000000000000000000000000000000
• Permit2 on Tempo: 0x000000000022d473030f116ddee9f6b43ac78ba3
• Tempo payment SDK: mppx (npm install mppx viem)
• USDC on Base (8453): 0x833589fCD6eDb6E08f4c7C32D4f71b54bdA02913
• USDbC on Base (8453): 0xd9aAEc86B65D86f6A7B5B1b0c42FFA531710b6CA
• USDC on Ethereum (1): 0xA0b86991c6218b36c1d19D4a2e9Eb0cE3606eB48
• WETH on Ethereum (1): 0xC02aaA39b223FE8D0A0e5C4F27eAD9083C756Cc2
• WETH on Base (8453): 0x4200000000000000000000000000000000000006
• Native ETH (all chains): 0x0000000000000000000000000000000000000000 (zero address, recommended for swaps)
• USDC-e on Arbitrum (42161): 0xFF970A61A04b1cA14834A43f5dE4533eBDDB5CC8
• Supported chains for Trading API: 1, 8453, 42161, 10, 137, 130
• x402 spec: https://github.com/coinbase/x402

Related Skills

• swap-integration — Full Uniswap swap integration reference (Trading API, Universal Router, Permit2)