uniswap-tx-builder-mcp

A keyless MCP server that builds unsigned Uniswap v3 liquidity-position transactions and optionally simulates them via eth_call. It never holds keys and never signs — you take the returned calldata and sign + broadcast it with your own wallet (viem, a CDP wallet MCP, any signer).

Because it's keyless, the only limits that apply to a built tx are your wallet's — the server's threat surface is just "it returns calldata and reads public RPCs."

Ecosystem

Part of Yummybait:

• cdp-wallet-agent-example — a reference agent that drives this MCP with a Coinbase CDP wallet as the signer.

• yummybait.finance — the product these tools power.

Related MCP server: MCP Wallet Signer

Tools

Every build tool returns tx = { to, data, value, chainId } plus rlp — the unsigned EIP-1559 (type-2) serialization of tx with nonce/fees/gas zeroed (signing services like the CDP API populate them; serialize tx yourself if you manage nonces) — and a human description. value is "0" except the payable Universal Router wrap/swap builds. Addresses are 0x…40; positionId and amounts are decimal strings (they exceed JS safe integers).

Encoding itself is offline: build_mint, build_increase, build_wrap, build_swap, and build_collect (with simulate: false) produce calldata without any network access. Only chain reads need a reachable RPC endpoint — and public defaults are baked in per chain, so nothing has to be configured either way (see Configuration to override them).

simulate runs an opt-in eth_call dry-run: on by default for collect/close, off for mint/increase (those need approvals + balances, so the dry-run usually reverts); wrap/swap/approve simulate when you pass sender (the signing wallet). A reverted simulation comes back as an error — don't sign a tx that failed to simulate. When a dry-run succeeds, the response also includes simulationResult — the actual decoded return value of the call (e.g. {amount0, amount1} for build_collect/build_close, {tokenId, liquidity, amount0, amount1} for build_mint, {approved} for build_approve) rather than just the simulated: true flag. build_wrap/build_swap go through the Universal Router's execute, which has no return value, so they only report simulated. See the companion skill for the full argument reference and position lifecycle.

Install & run

From npm (no clone, stdio transport — what MCP clients spawn):

npx -y @yummybait/uniswap-tx-builder-mcp

From source:

npm install
npm run dev                 # stdio MCP from source via tsx
npm run build && npm start  # compile to dist/, then run the built server
npm test                    # vitest

Set MCP_HTTP_PORT to serve the streamable-HTTP transport instead of stdio (endpoint: http://<host>:<port>/mcp). HTTP runs stateless — every POST gets a fresh server/transport pair, so any number of clients can connect and reconnect freely with no session bookkeeping:

MCP_HTTP_PORT=8102 npm run dev

Docker — build locally, or pull a released image from GHCR:

docker build -t uniswap-tx-builder-mcp:local .                        # local build
docker pull ghcr.io/yummybait-fin/uniswap-tx-builder-mcp:latest       # released image

docker run -i --rm uniswap-tx-builder-mcp:local                       # stdio
docker run --rm -p 8102:8102 -e MCP_HTTP_PORT=8102 uniswap-tx-builder-mcp:local  # HTTP

Connect to an MCP client

Claude Code (stdio via npm):

claude mcp add uniswap-tx-builder -- npx -y @yummybait/uniswap-tx-builder-mcp

Generic client config (Claude Desktop, etc.) — add to the client's mcpServers:

{
  "mcpServers": {
    "uniswap-tx-builder": {
      "command": "npx",
      "args": ["-y", "@yummybait/uniswap-tx-builder-mcp"],
      "env": { "RPC_ETH": "https://your-eth-rpc" }
    }
  }
}

(For a local build, swap the command for node /abs/path/to/uniswap-tx-builder-mcp/dist/mcp.js.)

For HTTP, run the server with MCP_HTTP_PORT and point the client at http://<host>:<port>/mcp.

Install the companion skill

skills/uniswap-tx-builder/ is a generic agent skill (no app- or wallet-specific knowledge) that teaches an agent how to drive these tools: the argument reference, simulate-first, the close→mint rebalance sequence, and the "your wallet signs" handoff. It pairs with the MCP — install both. Pick whichever install path suits you.

A. Claude Code plugin (/plugin) — the repo doubles as a plugin marketplace:

/plugin marketplace add Yummybait-fin/uniswap-tx-builder-mcp
/plugin install uniswap-tx-builder@yummybait

B. npx — copies the skill into a skills dir (no clone needed):

# personal (~/.claude/skills, every project)
npx -p @yummybait/uniswap-tx-builder-mcp uniswap-tx-builder-skill

# or project-scoped (./.claude/skills, checked in with a repo)
npx -p @yummybait/uniswap-tx-builder-mcp uniswap-tx-builder-skill --project

C. Manual copy — straight from a checkout:

cp -r skills/uniswap-tx-builder ~/.claude/skills/                       # personal
mkdir -p .claude/skills && cp -r skills/uniswap-tx-builder .claude/skills/  # project

The agent picks it up by its SKILL.md frontmatter — no restart needed for project skills.

Configuration

Per-chain RPCs default to public endpoints; override with env vars (see src/config.ts):

Public RPCs are rate-limited and best-effort — set your own for anything beyond casual use.

Architecture

One code path, transport kept separate so it stays testable and ready for a future v4 tool set:

builder.ts     calldata + unsigned-RLP encoding (viem), position/pool reads
ticks.ts       pure tick / sqrt-price / liquidity math (no I/O)
operations.ts  build + optional eth_call simulate + response shaping
server.ts      the MCP tool surface (schemas, registration, logging)
mcp.ts         transport bootstrap (stdio / stateless streamable HTTP)

CI / releases

GitHub Actions (.github/workflows/):

• CI — typecheck + tests + npm-tarball allowlist check on every push to main and on PRs.

• Release — pushing a v* tag re-runs the tests, bumps the version on main to match the tag (package.json + .claude-plugin/plugin.json), publishes the npm package (@yummybait/uniswap-tx-builder-mcp) with provenance, and builds + publishes the Docker image to GHCR (ghcr.io/yummybait-fin/uniswap-tx-builder-mcp), tagged with the version (and latest). The tag is the single version source for both artifacts; the bump lands on main after the tag, so the tagged commit keeps its old version.

git tag v0.3.0 && git push origin v0.3.0   # cut a release

npm supply-chain posture

The npm publish job is locked down; keep these properties when touching it:

• Trusted publishing (OIDC) — no long-lived npm token in CI. Configured on npmjs.com under package → Settings → Trusted publisher (GitHub Actions, this repo, release.yml). The NPM_TOKEN secret path in the workflow exists only to bootstrap the first release (trusted publishers can't be configured before the package exists) — delete the secret afterwards and set the package's publishing access to "Require two-factor authentication and disallow tokens".

• Provenance — publishConfig.provenance: true attaches a Sigstore attestation linking every published tarball to the exact workflow run and commit. It also makes an accidental local npm publish fail (no OIDC outside CI). Consumers verify with npm audit signatures.

• Gates before publish — npm audit signatures (registry attestations of the dep tree), npm audit --omit=dev --audit-level=high (no known high/critical vulns in shipped deps), typecheck + full test suite (prepublishOnly), and scripts/verify-tarball.mjs (the tarball must contain exactly the allowlisted files — no secrets, no strays).

• Hardened job — npm ci --ignore-scripts (no dependency postinstall runs where publish credentials live), minimal per-job permissions, actions pinned to commit SHAs, Dependabot keeping pins and deps fresh.

Scope

Uniswap v3 NonfungiblePositionManager on the chains above. Calling an unconfigured chain returns an "Unsupported chain" error. Roadmap: Uniswap v4 as a separate set of tools alongside these.