Jsonaut MCP Server

Jsonaut

JSON repair & validation built for AI agents as the customer. Send possibly-malformed JSON (LLM tool-call output, another agent's message, a flaky upstream), get back parsed, schema-valid JSON.

• Free tier: deterministic repair — trailing commas, single quotes, truncation, markdown code fences, comments, Python literals — plus JSON Schema validation with type coercion (string→number, defaults, stripping hallucinated fields). Rate-limited per IP.
• Paid tier: LLM-fallback repair for inputs the deterministic pass can't fix. $0.01/call, charged only on success, paid autonomously per-call via x402 (USDC on Base) — no accounts, no signup.

Business context, market research, and the full 3-day plan live in IDEA.md and PLAN.md.

Quickstart

npm install
npm test          # 27 tests: repair battery, schema coercion, HTTP API, MCP protocol
npm run dev       # http://localhost:8787 — demo page + API + MCP endpoint

Try it:

curl -s -X POST http://localhost:8787/v1/repair \
  -H "content-type: application/json" \
  -d "{\"input\": \"{'name': 'alice', 'count': '42',}\", \"schema\": {\"type\":\"object\",\"properties\":{\"count\":{\"type\":\"number\"}}}}"

{
  "valid": true,
  "repaired": { "name": "alice", "count": 42 },
  "method": "deterministic-repair",
  "changes": ["repaired JSON syntax (jsonrepair)", "$.count: coerced string \"42\" to number"]
}

API

Response method values: direct (was already valid), deterministic-repair (free fix), llm-repair (paid fix), failed. changes[] lists every modification so callers can audit what was done to their data.

Using it from an agent (MCP)

claude mcp add --transport http jsonaut https://YOUR-DEPLOYMENT/mcp

Or in any MCP client config:

{ "mcpServers": { "jsonaut": { "type": "http", "url": "https://YOUR-DEPLOYMENT/mcp" } } }

For the paid tier, clients pay via x402 and retry with the X-PAYMENT header (the payment receipt). No accounts or API keys — agents pay per call.

Payment flow (x402)

1. Agent calls /v1/repair with allow_llm_fallback: true; deterministic repair fails.
2. Server responds 402 with an x402 accepts array (USDC on Base, amount = PRICE_USD).
3. Agent pays and retries with the X-PAYMENT header; server verifies via the facilitator, runs the LLM repair, and settles only if the repair succeeds.

Configuration

Local dev secrets go in a .dev.vars file (git-ignored) or your shell env.

Deployment (Cloudflare Workers)

npx wrangler login
npx wrangler kv namespace create KV      # then paste the id into wrangler.toml
npx wrangler secret put OPENROUTER_API_KEY
npx wrangler deploy

The same codebase runs on Node for local dev (npm run dev) and on Workers in production — storage falls back to in-memory when no KV binding exists.

Project structure

src/core/      pipeline.ts (repair engine) · coerce.ts (schema coercion) · llm.ts (paid tier)
src/http/      app.ts (routes) · payment.ts (x402 rail) · ratelimit.ts · demo.ts · billing.ts (parked, unused)
src/mcp/       server.ts (stateless Streamable HTTP MCP server)
src/worker.ts  Cloudflare Workers entry
src/dev.ts     Node dev entry
test/          full battery: broken-JSON cases, coercion, HTTP, MCP protocol

Known limitations (MVP)

• Schema coercion does not resolve $ref or oneOf/anyOf branches.
• x402 verification requires an external facilitator (FACILITATOR_URL); there is no on-chain verification built in.
• Free-tier rate limiting is approximate under high concurrency (KV read-modify-write).