🐴 gulltoppr

A real session: an unverified MEV bot that traded seconds earlier (no source, no ABI anywhere) resolved to a full interface in two MCP tool calls.

The REST engine for abi.ninja-for-agents: the resolution ladder + verb surface that lets an AI agent go from (chain, address) to a correct, simulated, safe contract interaction. This is "the engine" of the four faces (REST → MCP → SDK → Skill); see ../SPEC.md for the full contract and ../IDEATION.md for the strategy.

TypeScript + viem + Hono. The heimdall decompile rung is delegated over HTTP to gulltoppr (kept out-of-process by design).

Run

npm install
npm run dev            # REST engine: tsx watch on http://localhost:8787
npm run mcp            # MCP server: stdio, 7 tools (for agent clients)
npm run mcp:http       # MCP server: Streamable HTTP (remote agents)
npm run typecheck      # tsc --noEmit
npm test               # vitest unit tests (cache, chains, ladder helpers, args, errors)
npm run test:live      # opt-in live contract smoke tests (RPC/decompiler/network)

Env

var	default	notes
PORT	8787
HEIMDALL_API_URL	https://heimdall-api.fly.dev	heimdall decompile service (ladder rung 4)
ETHERSCAN_API_KEY	(empty)	one multichain v2 key; empty disables rung 1
SIGNING_BASE_URL	https://abi.ninja	base for prepare_tx hand-off deeplinks
RATE_LIMIT	120	per-IP requests per window (fixed window); 0 disables
RATE_LIMIT_WINDOW_SEC	60	rate-limit window length
RATE_LIMIT_ALLOW	(empty)	comma-separated IP allowlist (exempt); private 6PN IPs are always exempt
ANTHROPIC_API_KEY	(empty)	enables the registry's LLM propose-and-verify pass on decompiles; empty disables
REGISTRY_LLM_MODEL	claude-opus-4-8	model for propose-and-verify

Endpoints (SPEC §4)

verb	route
resolve_abi	GET /v1/{chain}/{address}/abi
read_contract	POST /v1/{chain}/{address}/read · body {function, args}
encode_call	POST /v1/{chain}/{address}/encode · body {function, args, value?}
simulate	POST /v1/{chain}/simulate · body {from,to,data,value?} or {from,address,function,args,value?}
prepare_tx	POST /v1/{chain}/{address}/prepare · body {function, args, from, value?}
decode_tx	GET /v1/{chain}/tx/{hash}
resolve_name	GET /v1/{chain}/name/{name} · GET /v1/{chain}/name/by-address/{address}
chain catalog	GET /v1/chains · viem-backed aliases/default RPCs for UI clients
registry lookup	GET /v1/lookup/{selector} · 4-byte (function/error) or 32-byte (event topic0), chain-independent
registry stats	GET /v1/registry/stats

The registry (selector commons)

The engine seeds an open selector→signature registry as a byproduct of resolution:

• Every verified resolution (Etherscan/Sourcify) harvests ground-truth selector → signature pairs for functions, events (full 32-byte topic0, collision-free), and errors. Proof grade: verified-source.
• Resolutions are also indexed by skeleton hash (runtime bytecode with the solc metadata trailer stripped), so byte-identical clones resolve via a new bytecode-match rung without re-running the ladder. Verified claims are capped to partial for clones (this address's source was never verified).
• Decompiled ABIs get Unresolved_<selector> names replaced from proven registry entries, and (when ANTHROPIC_API_KEY is set) a fire-and-forget propose-and-verify pass asks Claude for candidate signatures and accepts only those where keccak256(sig)[:4] reproduces the selector: proof grade keccak-proven (signature proven; semantics still inferred).

Only the engine's own pipeline writes to the registry; no open submissions (that's how 4byte got collision-poisoned).

The accumulated data is published as a CC0 dataset: evm-abi-commons (regenerate any time from GET /v1/registry/export).

{chain} is any alias from GET /v1/chains (backed by viem/chains) or a numeric id. Pass ?rpc_url= to override the RPC (required for chains with no default, e.g. local/31337; this is how any EVM chain works before it has a built-in alias).

curl localhost:8787/v1/ethereum/0xC02aaA39b223FE8D0A0e5C4F27eAD9083C756Cc2/abi
curl -X POST localhost:8787/v1/ethereum/0xC02aaA39b223FE8D0A0e5C4F27eAD9083C756Cc2/prepare \
  -H 'content-type: application/json' \
  -d '{"function":"approve","args":["0x1111111254EEB25477B68fb85Ed929f73A960582","1000000000000000000"],"from":"0xd8dA6BF26964aF9D7eEd9e03E53415D37aA96045"}'

MCP server (SPEC §5)

npm run mcp starts a stdio MCP server exposing the same seven verbs as tools. The tools are a thin adapter over the deployed REST engine via gulltoppr (ENGINE_URL), so the MCP shares the engine's persistent cache and Etherscan key; no duplicated resolution or secrets. Tool descriptions bake in the non-custodial hand-off model (prepare_tx never signs) and lead with provenance warnings when an ABI is decompiled.

Wire it into an MCP client (Claude Desktop / Claude Code mcp config):

{
  "mcpServers": {
    "gulltoppr": {
      "command": "npm",
      "args": ["run", "--silent", "mcp"],
      "cwd": "/home/ubuntu/repos/abi-agent",
      "env": { "ETHERSCAN_API_KEY": "" }
    }
  }
}

Tools: resolve_abi, read_contract, encode_call, simulate, prepare_tx, decode_tx, resolve_name. All are read-only-annotated except prepare_tx (non-destructive: returns an unsigned hand-off, signs nothing).

Remote (Streamable HTTP)

For agents that can't run a local stdio server, the same MCP is hosted over HTTP at https://mcp.gulltoppr.dev/mcp (npm run mcp:http locally; stateless). Point an HTTP-capable MCP client at that URL:

{ "mcpServers": { "gulltoppr": { "url": "https://mcp.gulltoppr.dev/mcp" } } }

Tool registration is shared (src/mcp-server.ts) between the stdio entry (mcp.ts) and the HTTP entry (mcp-http.ts), deployed via Dockerfile.mcp / fly.mcp.toml.

npm SDK

A typed client over this REST surface lives in sdk/ (gulltoppr): new AbiNinja({ baseUrl }).resolveAbi(...) / .read(...) / .prepareTx(...), plus a contract() helper. It's the third face (after REST and MCP) and the basis for refactoring abi.ninja's frontend onto a shared client. See sdk/README.md.

Deploy

Live at https://api.gulltoppr.dev (Fly.io app gulltoppr, region cdg, co-located with gulltoppr to minimize ladder rung-4 latency). Containerized via the Dockerfile (Node 22, run with tsx; ~82 MB image), configured by fly.toml.

flyctl deploy --remote-only --ha=false
# optional: set an Etherscan v2 key to enable ladder rung 1
flyctl secrets set ETHERSCAN_API_KEY=... -a gulltoppr

HEIMDALL_API_URL / SIGNING_BASE_URL / PORT are set in fly.toml [env]. Machines auto-stop when idle and auto-start on request.

Claude Skill

The fourth face: a Claude Skill (skill/gulltoppr/) that teaches an agent the workflow (resolve → check provenance → read or prepare → simulate → hand off) and the non-custodial safety rules. Install with cp -r skill/gulltoppr ~/.claude/skills/gulltoppr. See skill/README.md.

Layout

src/
  server.ts        REST routes (Hono), BigInt-safe JSON, error mapping
  index.ts         REST entry / boot
  mcp.ts           MCP server (stdio): 7 tools over the same verbs
  config.ts        env + defaults
  chains.ts        alias/id → {id, viem chain, rpc}  (SPEC §6)
  clients.ts       cached viem PublicClients
  types.ts         the SPEC §2 data types
  errors.ts        typed ApiError → HTTP status  (SPEC §7)
  resolve/
    index.ts       resolve_abi: the ladder orchestrator (the spine)
    etherscan.ts   rung 1  · sourcify.ts rung 2 · proxy.ts rung 3
    heimdall.ts    rung 4 (gulltoppr) · fourbyte.ts rung 5
    interface.ts   capability manifest builder ("the buttons", SPEC §2.4a)
    selectFunction.ts  name/signature → AbiFunction
  verbs/
    read.ts encode.ts simulate.ts prepare.ts decodeTx.ts resolveName.ts
    args.ts        JSON-arg → viem-typed coercion

Status

Working end-to-end (verified against live mainnet): the full ladder, the capability manifest, read_contract, encode_call, prepare_tx (with eth_call simulation + deeplink + provenance warnings), decode_tx (via gulltoppr), and ENS resolve_name, all exposed over both the REST surface and the MCP server (stdio handshake + all 7 tools + a live tool call verified).

Stubbed / TODO (clearly marked in-code):

• 4byte rung 5: returns null; ladder ends in ABI_NOT_FOUND instead of a selector-only ABI. Needs bytecode selector scan + 4byte.directory lookup.
• simulate state_diff: empty; needs prestateTracer. asset_changes/logs come from debug_traceCall (callTracer) when the RPC supports it, else empty.
• basenames (*.base.eth): resolve_name only does mainnet ENS today.
• diamonds (EIP-2535): proxy detection covers 1967/UUPS/transparent/beacon/1167.
• decode_tx: doesn't yet layer a verified ABI over the heimdall decode for real event/param names.
• caching: no result cache yet; every resolve_abi re-runs the ladder (gulltoppr caches its own decompiles).