Korea Ground-Truth MCP

Headless, AI-native SaaS whose customer is an AI agent. Exposes Korean fact-verification tools over MCP (Streamable HTTP) and REST, metered with prepaid credits.

Live: https://kr-groundtruth-mcp.vercel.app — /llms.txt, /openapi.json, /pricing.json. MCP endpoint: /api/mcp.

claude mcp add --transport http kgt https://kr-groundtruth-mcp.vercel.app/api/mcp --header "Authorization: Bearer kgt_live_..."

Stack

Next.js 16 (App Router) · mcp-handler 2 (MCP SDK v2, stateless) · Supabase Postgres · Toss Payments · Vercel.

Related MCP server: MadTaco MCP Server

Infra

• Supabase project kr-groundtruth-mcp (ref kzjzjahokqduktphxpsj, ap-northeast-2)

• Vercel project chloepark85s-projects/kr-groundtruth-mcp; env vars set for production (vercel env ls)

• Listings: Official MCP Registry io.github.ChloePark85/kr-groundtruth (server.json + mcp-publisher), Smithery hapark85/kr-groundtruth (smithery mcp publish … --config-schema), Glama (auto-indexed; claimed via /.well-known/glama.json), mcp.so (issue chatmcp/mcpso#3776)

• MCP auth: discovery (initialize/tools/list) is public; tools/call needs a key via Authorization: Bearer, x-api-key, or ?apiKey=

Setup

1. Supabase project → run supabase/migrations/0001_core.sql in the SQL editor (or supabase db push).

2. Copy .env.example → .env.local, fill keys:

   • DATA_GO_KR_KEY: data.go.kr에서 「국세청_사업자등록정보 진위확인 및 상태조회」, 「국토교통부_아파트 매매 실거래가」 활용신청 (자동승인)

   • JUSO_KEY: business.juso.go.kr 승인키 신청

   • DART_KEY: opendart.fss.or.kr 인증키

   • LAW_OC: law.go.kr OPEN API 신청 (관리자 승인 1~2일)

   • TOSS_CLIENT_KEY / TOSS_SECRET_KEY: 토스페이먼츠 테스트 키

3. npm run dev

4. DART name search needs the corp code list: npx tsx scripts/sync-dart-corp-codes.ts (re-run monthly).

Flow

POST /v1/accounts {email}            → api_key (once) + free signup credits (SIGNUP_BONUS_CREDITS, 200 during launch)
claude mcp add --transport http kgt $URL/api/mcp --header "Authorization: Bearer kgt_live_..."
tools/call → debit_credits (row-locked) → cache → upstream → {ok, data, meta:{cost, balance_remaining}}
402 INSUFFICIENT_CREDITS → POST /v1/topups {credits} → checkout_url → human pays (Toss) → credit_credits (idempotent)

Design notes

• src/lib/tools/registry.ts is the single source for MCP tools, REST routes, OpenAPI, pricing and llms.txt. Prices are also seeded into tool_prices; the DB row is what debit_credits charges.

• Debit before upstream call; upstream failure → automatic refund (credit_ledger.reason='refund').

• credit_ledger is append-only (trigger) with unique(reason, ref_id), so Toss success-redirect and webhook can both run safely.

• All tables have RLS enabled with no policies; only the service-role key (server) can access them.

Metrics

• npm run metrics [-- --days 7 --include-test] — weekly report (north star = Weekly Active API Keys; funnel created → first call → 2nd-day call → 402 → top-up; time-to-first-call; calls by tool; revenue). Test accounts (@example.com) excluded unless --include-test.

• GET /v1/admin/metrics?days=7 with header x-admin-token: $ADMIN_TOKEN returns the same JSON (metrics_report() in supabase/migrations/0002_metrics.sql).

Verification checklist

H=http://localhost:3000
curl -X POST $H/v1/accounts -H 'content-type: application/json' -d '{"email":"a@b.com"}'
K=kgt_live_...
curl -X POST $H/api/mcp -H "Authorization: Bearer $K" -H 'accept: application/json, text/event-stream' -H 'content-type: application/json' \
  -d '{"jsonrpc":"2.0","id":1,"method":"tools/list"}'
curl -X POST $H/v1/tools/search_address -H "Authorization: Bearer $K" -H 'content-type: application/json' -d '{"keyword":"세종대로 209"}'
# race test: 50 concurrent calls on a low balance → ledger sum == balance
seq 50 | xargs -P 50 -I{} curl -s -o /dev/null -w '%{http_code}\n' -X POST $H/v1/tools/search_address -H "Authorization: Bearer $K" -H 'content-type: application/json' -d '{"keyword":"테스트 {}"}' | sort | uniq -c