/base-mcp

KyberSwap Plugin

[!IMPORTANT] Complete the short Base MCP onboarding flow defined in SKILL.md before calling any KyberSwap endpoint. The user's wallet address is fetched lazily when needed.

Overview

KyberSwap is a DEX aggregator that routes trades across 50+ liquidity sources (Uniswap V2/V3/V4, Curve, Balancer, and others) to find the best execution price across 7 chains. The plugin calls the KyberSwap Aggregator HTTP API to fetch a route quote and build unsigned calldata, then submits the result to Base MCP's send_calls. Use KyberSwap when the user wants the best rate across all available liquidity — not just a single protocol's pools.

Surface Routing

On chat-only surfaces where the allowlist is not configured: inform the user that the swap cannot proceed and direct them to the KyberSwap web UI at kyberswap.com. Do not improvise a workaround. For the full decision tree, see ../references/custom-plugins.md.

Endpoints

Base URL: https://aggregator-api.kyberswap.com/{chain}

Chain slugs: base · ethereum · arbitrum · optimism · polygon · bsc · avalanche

GET /api/v1/routes

Fetches the best route and returns a routeSummary required verbatim in the build step.

GET https://aggregator-api.kyberswap.com/{chain}/api/v1/routes
  ?tokenIn={address}
  &tokenOut={address}
  &amountIn={amountInWei}
  &to={walletAddress}
  &slippageTolerance={bps}
  &source=base-mcp

Response shape:

{
  "data": {
    "routeSummary": {
      "amountIn": "100000000",
      "amountInUsd": "100.00",
      "amountOut": "38650000000000000",
      "amountOutUsd": "99.71",
      "gas": "300000",
      "gasUsd": "0.29",
      "...": "other fields — pass verbatim to build step"
    },
    "routerAddress": "0x6131B5fae19EA4f9D964eAc0408E4408b66337b5"
  }
}

Keep the complete routeSummary object exactly as returned — it is required verbatim in the build step.

POST /api/v1/route/build

Builds encoded swap calldata from a previously fetched route.

{
  "url": "https://aggregator-api.kyberswap.com/{chain}/api/v1/route/build",
  "method": "POST",
  "headers": { "content-type": "application/json", "x-client-id": "base-mcp" },
  "body": {
    "routeSummary": { "...": "complete object from GET response" },
    "sender": "<walletAddress>",
    "recipient": "<walletAddress>",
    "slippageTolerance": 50,
    "deadline": "<current unix timestamp + 1200>",
    "source": "base-mcp"
  }
}

Do not modify or truncate routeSummary. Routes expire in ~30 seconds — if this step fails with "return amount is not enough", re-fetch the route and retry.

Response shape:

{
  "data": {
    "amountIn": "100000000",
    "amountOut": "38650000000000000",
    "gas": "300000",
    "transactionValue": "0",
    "routerAddress": "0x6131B5fae19EA4f9D964eAc0408E4408b66337b5",
    "data": "0x..."
  }
}

transactionValue is a decimal wei string (e.g. "0" for ERC-20 input, "10000000000000000" for 0.01 ETH). Hex-encode it before passing as value in send_calls: "0x" + BigInt(transactionValue).toString(16). Non-zero only for native token input.

GET /api/v1/public/tokens (token resolution)

Resolve a token symbol to its contract address when not in the known-addresses table in ## Notes.

GET https://token-api.kyberswap.com/api/v1/public/tokens
  ?chainIds={chainId}
  &name={symbol}
  &isWhitelisted=true

Pick the result with exact symbol match and highest marketCap. If no whitelisted match, retry without isWhitelisted.

Chain IDs: base=8453, ethereum=1, arbitrum=42161, optimism=10, polygon=137, bsc=56, avalanche=43114

Orchestration

Swap

1. get_wallets → walletAddress.
2. Resolve token symbols to addresses — use the ## Notes table first, then the token-api endpoint.
3. Compute amountIn in base units: multiply human amount by 10^decimals (ETH=18, USDC=6, WBTC=8).
4. Determine slippage: default 50 bps for common pairs, 100 bps for long-tail tokens. Apply thresholds in ## Risks & Warnings before proceeding.
5. GET /api/v1/routes → routeSummary, amountOut, amountOutUsd, gasUsd. Show the quoted output and gas cost to the user; confirm before proceeding.
6. POST /api/v1/route/build → data (swap calldata), transactionValue, routerAddress. Verify routerAddress equals 0x6131B5fae19EA4f9D964eAc0408E4408b66337b5 — abort and warn the user if it differs.
7. Build calls array:
   • Native tokenIn → [swap_call]
   • ERC-20 tokenIn → [approval_call, swap_call] — always include approval, no allowance check needed.
   • USDT on Ethereum — if existing allowance is non-zero, prepend a zero-approval call before the real approval.
8. send_calls(chain, calls) → approvalUrl, requestId.
9. Present approvalUrl to the user. Do not auto-approve. Call get_request_status(requestId) only after the user acts.

Submission

Target tool: send_calls

Map POST /route/build output into send_calls as follows:

ERC-20 tokenIn — approval + swap batch:

{
  "chain": "<chain string>",
  "calls": [
    {
      "to": "<tokenIn address>",
      "value": "0x0",
      "data": "<ERC-20 approve calldata>"
    },
    {
      "to": "0x6131B5fae19EA4f9D964eAc0408E4408b66337b5",
      "value": "<hex(transactionValue)>",
      "data": "<data from /route/build response>"
    }
  ]
}

Native tokenIn — swap only:

{
  "chain": "<chain string>",
  "calls": [
    {
      "to": "0x6131B5fae19EA4f9D964eAc0408E4408b66337b5",
      "value": "<hex(transactionValue)>",
      "data": "<data from /route/build response>"
    }
  ]
}

hex(transactionValue): "0x" + BigInt(transactionValue).toString(16) — transactionValue is a decimal wei string from the API.

ERC-20 approval calldata encoding:

Function: approve(address spender, uint256 amount)
Selector: 0x095ea7b3
spender:  000000000000000000000000{router without 0x}
amount:   {amountIn as 32-byte hex, left-padded with zeros}

Example — approve 100 USDC (amountIn = 100000000 = 0x5F5E100):
0x095ea7b3
  0000000000000000000000006131b5fae19ea4f9d964eac0408e4408b66337b5
  0000000000000000000000000000000000000000000000000000000005f5e100

Use chain name strings (base, ethereum, arbitrum, optimism, polygon, bsc, avalanche) — not numeric chain IDs. After send_calls returns an approval URL, follow the flow in ../references/approval-mode.md.

Example Prompts

"Swap 100 USDC to ETH on Base"

1. get_wallets → address.
2. GET /api/v1/routes on base — tokenIn=0x833589fCD6eDb6E08f4c7C32D4f71b54bdA02913 (USDC, 6 dec), tokenOut=0xEeee...eEEE, amountIn=100000000.
3. Show quoted output and gas to user; confirm.
4. POST /api/v1/route/build → data (swap calldata), transactionValue="0" → hex-encode to "0x0".
5. Encode approve calldata: router spends 100000000 USDC.
6. send_calls("base", [approval_call, swap_call]).

"Swap 0.1 ETH to USDC on Arbitrum"

1. get_wallets → address.
2. GET /api/v1/routes on arbitrum — tokenIn=0xEeee...eEEE, tokenOut=0xaf88d065e77c8cC2239327C5EDb3A432268e5831 (USDC), amountIn=100000000000000000.
3. Show quoted output and gas to user; confirm.
4. POST /api/v1/route/build → data (swap calldata), transactionValue="10000000000000000" → hex-encode to "0xde0b6b3a7640000" (non-zero, native input).
5. No approval needed — native ETH.
6. send_calls("arbitrum", [swap_call]) with value=transactionValue.

"What's the best rate to swap 500 MATIC to USDC on Polygon?" (read-only)

1. get_wallets → address.
2. GET /api/v1/routes on polygon — tokenIn=0xEeee...eEEE, tokenOut=0x3c499c542cEF5E3811e1192ce70d8cC03d5c3359 (USDC), amountIn=500000000000000000000.
3. Return amountOutUsd and gasUsd to the user — no transaction submitted.

Risks & Warnings

• Slippage — Swaps can fill materially worse than the quoted price if market conditions shift between quote and execution. Apply the following thresholds:

  Tolerance	Level	Action
  ≤ 100 bps (1%)	Normal	Proceed.
  > 100 and ≤ 500 bps (5%)	Elevated	Mention the value and ask the user to confirm.
  > 500 and ≤ 2000 bps (20%)	High	Warn that the trade can fill significantly below quote and is a likely sandwich target. Require explicit confirmation.
  > 2000 bps	Very high	Strongly warn; do not submit without the user re-confirming the exact number.

  If the user does not specify slippage, default to 50 bps for common pairs (ETH/USDC, WBTC/ETH) and 100 bps for long-tail or volatile tokens. Always pass an explicit value — the API defaults to 0 bps if slippageTolerance is omitted, causing most trades to fail.

Notes

Router address (same on all supported chains): 0x6131B5fae19EA4f9D964eAc0408E4408b66337b5

Native token sentinel (ETH/BNB/MATIC/AVAX/etc.): 0xEeeeeEeeeEeEeeEeEeEeeEEEeeeeEeeeeeeeEEeE

Common token addresses:

KyberSwap splits trades across multiple pools when beneficial — routeSummary may describe a multi-hop or split route. Pass it as-is; do not modify it.

USDT on Ethereum: if existing allowance is non-zero, the approve call will revert — send a zero-approval first (amount = 0x0...0), then the real approval.