JSON validator: is this valid JSON

$0.01 per call · failed calls are never charged · no account or subscription: pay per call with a card key or USDC

JSON validator: check whether a text is valid JSON and get the error position and message when it is not, plus the parsed type. Use before parsing an LLM's JSON output, saving a config or sending a request body.

Run it free (25 free calls) Buy credits by card (from $1) Example result (JSON)

Try it with your own inputs

The JSON text to check (up to 20,000 characters)

Uses one of your 25 free calls. Nothing is charged, and a call that fails is not counted.

Inputs

NameTypeDescription
text (required)stringThe JSON text to check (up to 20,000 characters)

Request

Over HTTP, with a card key from /credits:

curl -H "Authorization: Bearer adt_…" "https://tools.funwords.eu/json/validator?text=%7B%22a%22%3A1%7D"

Or one of your 25 free calls, no key:

curl "https://tools.funwords.eu/json/validator?text=%7B%22a%22%3A1%7D&trial=1"

Without a key, the same URL answers 402 Payment Required with x402 and MPP terms, so an agent with a wallet pays per call in USDC (Base, Polygon, Arbitrum or Solana over x402; Base or Tempo over MPP) and retries.

Example result

{
  "valid": true,
  "type": "object",
  "keys": 1
}

From an AI agent (MCP)

Add the MCP server to Claude, Cursor or any MCP client. This tool is json_validator, and the first 25 successful calls are free:

https://tools.funwords.eu/mcp

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