SmartContractExplainer MCP Server

PlainText — wallet approval translator

· Live status

Built on presign-guard: PlainText's verdicts now come from presign-guard (the same checks, sanctions list, wallet age and signed receipt); PlainText adds the explanation in plain language for people. POST /api/check-wallet ($0.04) uses presign-guard's approval audit, POST /api/explain ($0.03) its pre-sign check when the payload is a real approval, transaction or typed-data signature (anything else is explained by the model alone, source: "model"). Agents that only need the verdict and reason codes can call presign-guard directly ($0.01–$0.02). Needs FIZZL_INTERNAL_KEY (the same value on both services, Render only); without it the old path (GoPlus + Claude) runs.

A small Node.js app that looks up a wallet's token/NFT approvals via the GoPlus Security API and asks Claude to explain them in plain language.

▶ Watch the 1-minute explainer · Live: https://plaintext.fizzl.eu

Project structure

plaintext-wallet/
├── server.js          Express backend (GoPlus + Anthropic calls)
├── media.js           Serves the explainer video from the explainer-video branch
├── feedback.js        POST /feedback and the MCP tool feedback (same file in every Fizzl service)
├── media/explainer/   Script and pipeline for the explainer video
├── package.json
├── render.yaml         Render deploy config (optional, see below)
├── .env.example         Copy to .env for local dev
└── public/
    └── index.html      Frontend (wallet check + demo scenarios)

Feedback

Found a bug, or missing something? Send it with POST /feedback (free, no payment) or the MCP tool feedback:

curl -X POST https://plaintext.fizzl.eu/feedback \
  -H 'content-type: application/json' \
  -d '{"type": "feature", "message": "Support Solana wallets", "endpoint": "/api/check-wallet"}'

type is bug, feature or other; message is required (up to 2000 characters); endpoint and contact are optional. The answer is 202 with an id. At most 10 reports per hour per caller. Reports go to the usage log, and a person reads every one; nothing in a report is run or changed automatically. GET /feedback shows the schema.

1. Run it locally first

cd plaintext-wallet
npm install
cp .env.example .env
# edit .env and paste your ANTHROPIC_API_KEY
npm start

Open http://localhost:3000 — try the "Try a sample" tab first (no API keys needed besides Anthropic), then "Check a wallet" with a real address once you're happy it works.

2. Deploy to Render

Option A — one-click via render.yaml (Blueprint)

1. Push this folder to a new GitHub repo.
2. In the Render dashboard: New + → Blueprint → select your repo. Render reads render.yaml automatically and creates the web service.
3. When prompted, fill in the environment variables:
   • ANTHROPIC_API_KEY — required, from console.anthropic.com
   • GOPLUS_ACCESS_TOKEN — optional, only needed if you outgrow GoPlus's free 30 calls/minute limit (see console.gopluslabs.io)
4. Click Apply — Render builds and deploys automatically.

Option B — manual web service (no render.yaml needed)

1. Push this folder to a GitHub repo.
2. Render dashboard → New + → Web Service → connect your repo.
3. Settings:
   • Environment: Node
   • Build Command: npm install
   • Start Command: npm start
   • Instance Type: Free (fine for a prototype)
4. Under Environment Variables, add ANTHROPIC_API_KEY (and optionally GOPLUS_ACCESS_TOKEN).
5. Click Create Web Service. Render gives you a https://<name>.onrender.com URL once the build finishes.

Render's free tier spins the service down after inactivity — the first request after idling will take ~30-50 seconds to wake up. That's normal and fine for a prototype you're sharing for feedback.

Notes on the GoPlus integration

• The wallet check calls token_approval_security or nft721_approval_security under https://api.gopluslabs.io/api/v2/.... This is documented but the GoPlus docs site is JS-rendered, so before you rely on this in front of real users, do one manual test call (e.g. with curl) against a wallet you control, and compare the actual JSON shape to what server.js expects — field names occasionally shift between GoPlus API versions.
• The free GoPlus tier is capped at 30 calls/minute — plenty for early testing, but rate-limit errors will surface as a plain error message in the UI if you exceed it.
• No user data is stored anywhere in this app — every check is a stateless round trip. If you later add accounts, saved wallets, or history, update this note (and your own privacy policy) accordingly.

Costs to expect

• Render free tier: $0/month, with the cold-start behavior above. A paid tier ($7/month "Starter") removes the spin-down if this gets real usage.
• Anthropic API: pay-per-use, billed to whatever key you provide. A single explanation call is small (well under 1K tokens), so cost per check will be a fraction of a cent — but keep an eye on your usage dashboard if this gets shared widely, since there's no rate limiting built into this prototype yet.