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. $0.01/call, charged only on success, paid autonomously per-call via x402 (USDC on Base) — no accounts, no signup.
Business context, market research, and the full 3-day plan live in IDEA.md and PLAN.md.
Quickstart
npm install
npm test
npm run dev
Try it:
curl -s -X POST http://localhost:8787/v1/repair \
-H "content-type: application/json" \
-d "{\"input\": \"{'name': 'alice', 'count': '42',}\", \"schema\": {\"type\":\"object\",\"properties\":{\"count\":{\"type\":\"number\"}}}}"
{
"valid": true,
"repaired": { "name": "alice", "count": 42 },
"method": "deterministic-repair",
"changes": ["repaired JSON syntax (jsonrepair)", "$.count: coerced string \"42\" to number"]
}
API
| Route | What it does |
|---|
POST /v1/repair | Repair + optional schema validation/coercion. Body: {input, schema?, allow_llm_fallback?} |
POST /v1/validate | Validate only, no repair. Body: {input, schema} |
POST /mcp | MCP server (Streamable HTTP, stateless). Tools: repair_json, validate_json |
GET / | Interactive demo page |
GET /llms.txt | Agent-readable capability + pricing description |
GET /openapi.yaml | OpenAPI 3.1 spec |
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)
- Agent calls
/v1/repair with allow_llm_fallback: true; deterministic repair fails.
- Server responds
402 with an x402 accepts array (USDC on Base, amount = PRICE_USD).
- 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
| Env var | Purpose | Required for |
|---|
OPENROUTER_API_KEY | Enables the paid LLM-fallback tier (via OpenRouter; free model by default) | Paid tier |
OPENROUTER_MODEL | Override the model (default meta-llama/llama-3.3-70b-instruct:free) | — |
X402_PAY_TO | Wallet address on Base receiving USDC | x402 rail |
X402_NETWORK | base or base-sepolia (default base) | x402 rail |
FACILITATOR_URL | x402 facilitator for verify/settle | x402 rail |
FREE_DAILY_LIMIT | Free calls per IP per day (default 100) | — |
PRICE_USD | Paid-tier price (default 0.01) | — |
DEV_ALLOW_FREE_LLM | true opens the paid tier for local dev only | — |
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
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).