Swap Approve

KyberSwap Approve Skill

Manage ERC-20 token approvals for the KyberSwap router. Check current allowance, approve exact amounts, approve unlimited, or revoke approvals using Foundry's cast.

Prerequisites

• Foundry installed: cast must be available in PATH
• Wallet configured: One of the methods below (only needed for setting/revoking approvals, not for checking allowance)
• Native token for gas: Approval transactions cost gas (~46k gas for standard ERC-20)

Wallet Setup (One-Time)

⚠️ USE YOUR EXISTING WALLET MANAGEMENT FIRST ⚠️

If you or your agent already have wallet management (key management service, vault, HSM, custodial API, MPC signer, or any secure signing infrastructure), use that. Skip the examples below entirely.

The wallet options below are example setups for development and testing only. They have known security issues: plaintext password files on disk, private keys in shell environments, no access control, no audit trail, no key rotation. Do not use them with real funds in production.

Option A: Encrypted Keystore (Recommended)

cast wallet import mykey --interactive
# Enter private key, then set encryption password

# Create password file securely (prompts without echoing to terminal)
printf "Password: " && read -s pw && printf '\n' && echo "$pw" > ~/.foundry/.password && chmod 600 ~/.foundry/.password

Option B: Environment Variable Set the key in your current shell session only (do not persist to shell profiles):

printf "Enter private key: " && read -s PRIVATE_KEY && printf '\n' && export PRIVATE_KEY

Option C: Ledger Hardware Wallet

• Connect Ledger, open Ethereum app
• No setup needed, will prompt for physical confirmation

See ${CLAUDE_PLUGIN_ROOT}/skills/swap-execute/references/wallet-setup.md for detailed instructions.

NEVER echo, print, log, or display any private key value, even in error messages or debug output.

Input Parsing

The user will provide input like:

• check USDC allowance on ethereum for 0xAbc123...
• approve 100 USDC on arbitrum from 0xAbc123...
• approve unlimited LINK on base from 0xAbc123...
• revoke USDT approval on ethereum from 0xAbc123...

Extract these fields:

• token — the token symbol (e.g., USDC, LINK)
• chain — the chain slug (default: ethereum)
• sender — the wallet address (required)
• amount — the amount to approve (optional):
  • Omitted or "check" = check current allowance only
  • A number (e.g., 100, 0.5) = approve that exact amount
  • "unlimited" or "max" = approve type(uint256).max
  • "0" or "revoke" = revoke approval (set allowance to 0)

If the sender address is not provided, ask the user for it before proceeding. Do not guess or use a placeholder address.

Sender address validation — reject or warn before proceeding:

• Must not be the zero address (0x0000000000000000000000000000000000000000) — invalid sender.
• Must not be the native token sentinel (0xEeeeeEeeeEeEeeEeEeEeeEEEeeeeEeeeeeeeEEeE) — this is a placeholder, not a real account.
• Must match format ^0x[a-fA-F0-9]{40}$ — reject malformed addresses.

Router Address

The KyberSwap router address is the same on all supported chains:

0x6131B5fae19EA4f9D964eAc0408E4408b66337b5

Workflow

Step 1: Validate Input

1. Verify the sender address is provided and valid.
2. Reject native tokens — if the user asks to approve ETH, BNB, MATIC/POL, AVAX, MNT, S, BERA, RON, XTZ, or MON, explain:

Native tokens (ETH, BNB, MATIC, etc.) do not use the ERC-20 approval mechanism. They are sent directly as msg.value in the transaction. No approval is needed to swap native tokens through the KyberSwap router.

If the user intended the wrapped version (WETH, WBNB, WMATIC, etc.), suggest they specify the wrapped token symbol instead.

Step 2: Resolve Token Address

Read the token registry at ${CLAUDE_PLUGIN_ROOT}/references/token-registry.md.

Look up the token for the specified chain. Match case-insensitively. Note the decimals for the token.

If the token is not found in the registry: Use the fallback sequence described at the bottom of ${CLAUDE_PLUGIN_ROOT}/references/token-registry.md:

1. KyberSwap Token API (preferred) — search whitelisted tokens first: https://token-api.kyberswap.com/api/v1/public/tokens?chainIds={chainId}&name={symbol}&isWhitelisted=true via WebFetch. Pick the result whose symbol matches exactly with the highest marketCap. If no whitelisted match, retry without isWhitelisted.
2. CoinGecko API (secondary fallback) — search CoinGecko for verified contract addresses.
3. Ask user manually (final fallback) — ask the user for the contract address and decimals. Never guess or fabricate addresses.

Step 3: Check Current Allowance

Determine the RPC URL for the chain:

Or the user can specify a custom RPC with --rpc-url.

Run the allowance check:

cast call \
  --rpc-url {RPC_URL} \
  {tokenAddress} \
  "allowance(address,address)(uint256)" \
  {sender} \
  0x6131B5fae19EA4f9D964eAc0408E4408b66337b5

Convert the result from wei to human-readable using the token's decimals:

humanAllowance = allowanceWei / 10^(token decimals)

Display the current allowance:

## Current Allowance

| Detail | Value |
|--------|-------|
| Token | {symbol} (`{tokenAddress}`) |
| Chain | {chain} |
| Owner | `{sender}` |
| Spender (Router) | `0x6131B5fae19EA4f9D964eAc0408E4408b66337b5` |
| Current allowance | {humanAllowance} {symbol} |

If the allowance equals 115792089237316195423570985008687907853269984665640564039457584007913129639935 (type(uint256).max), display it as "Unlimited" instead of the raw number.

Step 4: Determine Action

• Check only (no amount specified): Display allowance from Step 3 and stop.
• Approval needed (amount specified): Compare current allowance to requested amount.
  • If current allowance >= requested amount: Inform the user the approval is already sufficient. Ask if they still want to set a new approval.
  • If current allowance < requested amount: Proceed to Step 5.
• Revoke (amount = 0): Proceed to Step 5 regardless of current allowance (unless already 0).
• Unlimited: Proceed to Step 5 (unless already unlimited).

Step 5: Confirm Approval

CRITICAL: Always confirm before executing. Approval transactions are on-chain and cost gas.

Present the approval details:

## Token Approval -- Confirmation Required

| Detail | Value |
|--------|-------|
| Token | {symbol} ({tokenAddress}) |
| Chain | {chain} |
| Spender (Router) | 0x6131B5fae19EA4f9D964eAc0408E4408b66337b5 |
| Current allowance | {currentAllowance} {symbol} |
| New allowance | {requestedAmount} {symbol} |
| Sender | {sender} |

{WARNING}

Do you want to proceed? (yes/no)

Warnings by type:

• Exact amount: "This approves the router to spend exactly {amount} {symbol} from your wallet."
• Unlimited: "SECURITY WARNING: Unlimited approvals allow the router to spend ALL your {symbol} tokens. If the router contract is ever compromised, an attacker could drain your entire {symbol} balance. Only use with wallets holding limited funds. For large holdings, prefer exact-amount approvals."
• Revoke (amount=0): "This removes the router's permission to spend your {symbol}. Existing pending swaps using this token will fail."

Wait for explicit "yes" confirmation before proceeding.

Step 6: Execute Approval

After user confirms, ask for wallet method (if not already specified):

How do you want to sign this transaction?

1. Keystore (encrypted key at ~/.foundry/keystores/)
2. Environment variable ($PRIVATE_KEY)
3. Ledger hardware wallet
4. Trezor hardware wallet

Wallet flags summary:

Determine the approval amount in wei:

Build and execute the cast send command:

Option 1: Keystore + Password File (Recommended)

cast send \
  --rpc-url {RPC_URL} \
  --account {keystore_name} \
  --password-file ~/.foundry/.password \
  {tokenAddress} \
  "approve(address,uint256)" \
  0x6131B5fae19EA4f9D964eAc0408E4408b66337b5 \
  {amountInWei}

Option 2: Environment Variable

cast send \
  --rpc-url {RPC_URL} \
  --private-key $PRIVATE_KEY \
  {tokenAddress} \
  "approve(address,uint256)" \
  0x6131B5fae19EA4f9D964eAc0408E4408b66337b5 \
  {amountInWei}

Option 3: Ledger

cast send \
  --rpc-url {RPC_URL} \
  --ledger \
  {tokenAddress} \
  "approve(address,uint256)" \
  0x6131B5fae19EA4f9D964eAc0408E4408b66337b5 \
  {amountInWei}

Option 4: Trezor

cast send \
  --rpc-url {RPC_URL} \
  --trezor \
  {tokenAddress} \
  "approve(address,uint256)" \
  0x6131B5fae19EA4f9D964eAc0408E4408b66337b5 \
  {amountInWei}

Step 7: Verify Approval

After the approval transaction confirms, re-check the allowance to verify it was set correctly:

cast call \
  --rpc-url {RPC_URL} \
  {tokenAddress} \
  "allowance(address,address)(uint256)" \
  {sender} \
  0x6131B5fae19EA4f9D964eAc0408E4408b66337b5

Present the result:

On success:

## Approval Confirmed

| Field | Value |
|-------|-------|
| Transaction Hash | `{txHash}` |
| Block Number | {blockNumber} |
| Gas Used | {gasUsed} |
| New allowance | {verifiedAllowance} {symbol} |

**Explorer Link:** {explorerUrl}/tx/{txHash}

The KyberSwap router can now spend up to {verifiedAllowance} {symbol} from your wallet.

On failure:

## Approval Failed

**Error:** {error message}

See Common Errors below for troubleshooting.

Explorer URLs by chain:

ethers.js Alternative

For agents or environments without Foundry, use ethers.js:

const { ethers } = require("ethers");

const RPC_URL = "https://ethereum-rpc.publicnode.com";
const ROUTER = "0x6131B5fae19EA4f9D964eAc0408E4408b66337b5";

const provider = new ethers.JsonRpcProvider(RPC_URL);
const signer = new ethers.Wallet(privateKey, provider);
const token = new ethers.Contract(tokenAddress, [
  "function allowance(address,address) view returns (uint256)",
  "function approve(address,uint256) returns (bool)",
  "function decimals() view returns (uint8)"
], signer);

// Check allowance
const allowance = await token.allowance(sender, ROUTER);
console.log("Current allowance:", ethers.formatUnits(allowance, decimals));

// Approve exact amount
const amountWei = ethers.parseUnits(amount, decimals);
const tx = await token.approve(ROUTER, amountWei);
await tx.wait();

// Approve unlimited
const unlimited = ethers.MaxUint256;
const tx2 = await token.approve(ROUTER, unlimited);
await tx2.wait();

// Revoke
const tx3 = await token.approve(ROUTER, 0n);
await tx3.wait();

Important Notes

• Native tokens do not need approval — ETH, BNB, MATIC, AVAX, etc. are sent directly as transaction value.
• Approvals are per-token-per-spender — approving USDC for the router does not approve USDT. Each token requires its own approval.
• Approval transactions cost gas — approximately 46k gas for a standard ERC-20 approve call.
• USDT on Ethereum mainnet requires setting allowance to 0 before changing to a new non-zero value. If an approval fails, suggest: "Try revoking first (set allowance to 0), then approve the desired amount."
• Never expose private keys in command output or logs.
• Verify router address matches expected: 0x6131B5fae19EA4f9D964eAc0408E4408b66337b5

Common Errors

Additional Resources

Reference Files

• ${CLAUDE_PLUGIN_ROOT}/references/api-reference.md — Full API specification, error codes, rate limiting
• ${CLAUDE_PLUGIN_ROOT}/references/token-registry.md — Token addresses and decimals by chain

Troubleshooting

For errors not covered above (API errors, PMM/RFQ failures, full error code catalog), refer to ${CLAUDE_PLUGIN_ROOT}/skills/error-handling/SKILL.md.