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ValidationStation

by skwerl-hub
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Python
Remote

Self-Healing JSON Validator — MCP Server

Production-grade JSON repair and validation for agent pipelines. Automatically fixes malformed LLM output using Gemini, then validates against your JSON Schema. Built for agents that need data integrity without human intervention.

$0.025 per successful call. Fully automated. No humans involved.

Why This Exists

LLMs generate broken JSON constantly — trailing commas, unquoted keys, truncated strings, wrong types. Passing that output raw to an API or database causes hard crashes and silent data corruption. This tool is the safety net between your generator and your consumers.

Related MCP server: json-validator

How It Works

Every call runs through three stages:

raw_input
    │
    ▼
Stage 1: Strict JSON parse      → PASS → Stage 3
    │ FAIL
    ▼
Stage 2: LLM repair (Gemini)    → re-parse → PASS → Stage 3
    │ FAIL
    ▼
REPAIR_PARSE_FAILURE error with remediation instructions
    
Stage 3: JSON Schema validation → PASS → ✅ validated_data returned
    │ FAIL
    ▼
SCHEMA_VALIDATION_FAILURE error with per-field error list

Getting Started

1. Register for an API key

curl -X POST https://mcp-json-validator-production.up.railway.app/register \
  -H "Content-Type: application/json" \
  -d '{"email": "you@example.com"}'

Returns:

{
  "api_key": "mcpjv_...",
  "checkout_url": "https://checkout.stripe.com/...",
  "billing": "Metered — $0.025 per successful call, billed monthly via Stripe."
}

Visit the checkout_url to add your payment method. Your key works immediately.

2. Connect to the MCP server

https://mcp-json-validator-production.up.railway.app/sse

3. Call the tool

{
  "tool": "sanitize_and_validate_json",
  "arguments": {
    "api_key": "mcpjv_your_key_here",
    "raw_input": "{'name': 'Alice', 'age': '30', scores: [95, 87,]}",
    "target_schema": {
      "type": "object",
      "required": ["name", "age", "scores"],
      "properties": {
        "name":   { "type": "string" },
        "age":    { "type": "integer" },
        "scores": { "type": "array", "items": { "type": "number" } }
      }
    }
  }
}

Response:

{
  "status": "valid",
  "repair_applied": true,
  "validated_data": { "name": "Alice", "age": 30, "scores": [95, 87] },
  "message": "JSON is valid and satisfies the target schema. Syntax was automatically repaired."
}

Error Codes

Code

Meaning

What to do

FORBIDDEN

Invalid or missing api_key

Register at /register

EMPTY_INPUT

raw_input was empty

Check upstream step produced output

INVALID_SCHEMA

target_schema missing or not an object

Fix schema definition

MALFORMED_SCHEMA

target_schema fails JSON Schema meta-validation

Check for typos in schema keywords

REPAIR_PARSE_FAILURE

LLM repair failed to produce valid JSON

Regenerate raw_input from scratch

REPAIR_UNAVAILABLE

Repair stage unavailable

Check server status

SCHEMA_VALIDATION_FAILURE

JSON valid but structure wrong

Read validation_errors, fix and retry

Self-Healing Loop Pattern

When you receive SCHEMA_VALIDATION_FAILURE, feed the errors back to your generator:

Your previous output had these schema violations:
<validation_errors from tool response>

Regenerate the JSON correcting every violation listed above.

Then call the tool again. Limit retries to 3 before escalating.

Endpoints

Endpoint

Method

Purpose

/sse

GET

MCP connection point

/register

POST

Get an API key

/health

GET

Server health check

/.well-known/mcp/server-card.json

GET

Smithery discovery

Pricing

$0.025 per successful call, billed monthly via Stripe. You are only charged when the tool returns status: valid. Failed calls (auth errors, schema errors) are free.

License

MIT

This server cannot be deployed

Shareable, User-Owned Context BackendPeople, applications, and agents read, write, and coordinate together in one context lake. Reach it over MCP, a CLI, a Python SDK, or REST.fulcradynamics.comAd

Maintenance

ActivityInactive
ResponsivenessNo issues

Resources

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