API Documentation

Base URL: https://api.jsonfmt.dev

Introduction

The jsonfmt.dev API provides endpoints for formatting, minifying, validating, repairing, diffing, and converting JSON. All endpoints accept and return JSON over HTTPS.

Make your first call in 30 seconds -- no API key required:

curl -X POST https://api.jsonfmt.dev/format \
  -H "Content-Type: application/json" \
  -d '{"name":"Alice","age":30}'

const res = await fetch('https://api.jsonfmt.dev/format', {
  method: 'POST',
  headers: { 'Content-Type': 'application/json' },
  body: '{"name":"Alice","age":30}'
});
console.log(await res.text());

import requests

r = requests.post('https://api.jsonfmt.dev/format',
    headers={'Content-Type': 'application/json'},
    json={"name": "Alice", "age": 30})
print(r.text)

Response:

{
  "name": "Alice",
  "age": 30
}

Authentication

The API works without authentication at 10 requests/minute. For higher limits, get a free API key and pass it as a Bearer token:

curl -X POST https://api.jsonfmt.dev/format \
  -H "Authorization: Bearer jfmt_your_key_here" \
  -H "Content-Type: application/json" \
  -d '{"a":1}'

Every response includes rate-limit headers:

X-RateLimit-Limit: 10
X-RateLimit-Remaining: 7
X-RateLimit-Reset: 1710500060

POST /format

POST/format

Pretty-print JSON with 2-space indentation. Send any valid JSON as the request body.

curl -X POST https://api.jsonfmt.dev/format \
  -H "Content-Type: application/json" \
  -d '{"name":"Alice","age":30,"active":true}'

const res = await fetch('https://api.jsonfmt.dev/format', {
  method: 'POST',
  headers: { 'Content-Type': 'application/json' },
  body: '{"name":"Alice","age":30,"active":true}'
});
console.log(await res.text());

import requests
r = requests.post('https://api.jsonfmt.dev/format',
    json={"name": "Alice", "age": 30, "active": True})
print(r.text)

Try It

POST /minify

POST/minify

Remove all whitespace from JSON. Returns the most compact representation.

curl -X POST https://api.jsonfmt.dev/minify \
  -H "Content-Type: application/json" \
  -d '{  "a" : 1 ,  "b" : 2  }'

const res = await fetch('https://api.jsonfmt.dev/minify', {
  method: 'POST',
  headers: { 'Content-Type': 'application/json' },
  body: '{  "a" : 1 ,  "b" : 2  }'
});
console.log(await res.text());

import requests
r = requests.post('https://api.jsonfmt.dev/minify',
    data='{  "a" : 1 ,  "b" : 2  }',
    headers={'Content-Type': 'application/json'})
print(r.text)

Try It

POST /validate

POST/validate

Check if input is valid JSON. Returns validity status and byte count, or the parse error message.

curl -X POST https://api.jsonfmt.dev/validate \
  -H "Content-Type: application/json" \
  -d '{"valid": true}'

const res = await fetch('https://api.jsonfmt.dev/validate', {
  method: 'POST',
  headers: { 'Content-Type': 'application/json' },
  body: '{"valid": true}'
});
console.log(await res.json());

import requests
r = requests.post('https://api.jsonfmt.dev/validate',
    json={"valid": True})
print(r.json())

Try It

POST /repair

POST/repair

Fix broken JSON. Handles comments, trailing commas, single quotes, unquoted keys, Python literals (True/False/None), and undefined.

curl -X POST https://api.jsonfmt.dev/repair \
  -H "Content-Type: application/json" \
  -d "{name: 'Alice', active: True, tags: [1,2,],}"

const res = await fetch('https://api.jsonfmt.dev/repair', {
  method: 'POST',
  headers: { 'Content-Type': 'application/json' },
  body: "{name: 'Alice', active: True}"
});
console.log(await res.json());

import requests
r = requests.post('https://api.jsonfmt.dev/repair',
    data="{name: 'Alice', active: True}",
    headers={'Content-Type': 'application/json'})
print(r.json())

Try It

POST /diff

POST/diff

Compare two JSON documents. Send an object with "a" and "b" keys. Returns a list of changes (add, remove, replace).

curl -X POST https://api.jsonfmt.dev/diff \
  -H "Content-Type: application/json" \
  -d '{"a":{"name":"Alice","age":28},"b":{"name":"Alice","age":29,"role":"admin"}}'

const res = await fetch('https://api.jsonfmt.dev/diff', {
  method: 'POST',
  headers: { 'Content-Type': 'application/json' },
  body: JSON.stringify({
    a: { name: "Alice", age: 28 },
    b: { name: "Alice", age: 29, role: "admin" }
  })
});
console.log(await res.json());

import requests
r = requests.post('https://api.jsonfmt.dev/diff',
    json={"a": {"name": "Alice", "age": 28},
          "b": {"name": "Alice", "age": 29, "role": "admin"}})
print(r.json())

Try It

POST /convert/:format

POST/convert/:format

Convert JSON to 32 different output formats. Replace :format in the URL with any format from the table below.

Available Formats

Format	Path	Output	Status
Data Formats
YAML	`/convert/yaml`	YAML config	Live
CSV	`/convert/csv`	Comma-separated values	Live
XML	`/convert/xml`	XML document	Live
TOML	`/convert/toml`	TOML config	Live
Markdown	`/convert/markdown`	Markdown table	Live
.env	`/convert/dotenv`	Dotenv format	Live
Base64 Encode	`/convert/base64`	Base64 string	Live
Base64 Decode	`/convert/base64decode`	Decoded JSON	Live
Code Generators
TypeScript	`/convert/typescript`	TS interface	Live
Python	`/convert/python`	Python dataclass	Live
Go	`/convert/go`	Go struct	Live
Rust	`/convert/rust`	Rust struct (serde)	Live
Java	`/convert/java`	Java POJO	Live
C#	`/convert/csharp`	C# class	Live
Kotlin	`/convert/kotlin`	Kotlin data class	Live
Swift	`/convert/swift`	Swift Codable struct	Live
Dart	`/convert/dart`	Dart class	Live
PHP	`/convert/php`	PHP array	Live
Ruby	`/convert/ruby`	Ruby hash	Live
Schema & Validation
Zod	`/convert/zod`	Zod schema	Live
PropTypes	`/convert/proptypes`	React PropTypes	Live
Mongoose	`/convert/mongoose`	Mongoose schema	Live
GraphQL	`/convert/graphql`	GraphQL SDL	Live
OpenAPI	`/convert/openapi`	OpenAPI 3.0 schema	Live
Protobuf	`/convert/protobuf`	Protobuf schema	Live
JSON Schema	`/convert/jsonschema`	Draft-07 schema	Live
Mermaid	`/convert/mermaid`	Mermaid diagram	Live
Database
SQL Insert	`/convert/sql`	SQL INSERT statements	Live
SQL DDL	`/convert/sqlddl`	CREATE TABLE	Live
MongoDB	`/convert/mongodb`	MongoDB insert	Live
Transform
Flatten	`/convert/flatten`	Dot-notation keys	Live
Unflatten	`/convert/unflatten`	Nested JSON	Live
CSV → JSON	`/convert/csv2json`	JSON array	Live

Example Request

curl -X POST https://api.jsonfmt.dev/convert/yaml \
  -H "Content-Type: application/json" \
  -d '{"name":"Alice","skills":["go","rust","python"]}'

const res = await fetch('https://api.jsonfmt.dev/convert/yaml', {
  method: 'POST',
  headers: { 'Content-Type': 'application/json' },
  body: '{"name":"Alice","skills":["go","rust","python"]}'
});
console.log(await res.text());

import requests
r = requests.post('https://api.jsonfmt.dev/convert/yaml',
    json={"name": "Alice", "skills": ["go", "rust", "python"]})
print(r.text)

Try It

Format:

GET /health

GET/health

Health check endpoint. Returns current status and ISO timestamp. No authentication required.

curl https://api.jsonfmt.dev/health

Response:

{ "status": "ok", "timestamp": "2026-03-15T12:00:00.000Z" }

Tools

JSON transformation and analysis endpoints. All accept POST with JSON body.

Endpoint	Description	Body Format
`/compact`	Smart compact formatting	Raw JSON
`/sort-keys`	Sort object keys alphabetically	Raw JSON
`/escape`	JSON-escape a string	Raw string
`/unescape`	Unescape a JSON string	JSON string
`/redact`	Redact sensitive values (passwords, tokens, keys)	Raw JSON
`/pick`	Keep only specified keys	`{"input":{...}, "keys":["a","b"]}`
`/omit`	Remove specified keys	`{"input":{...}, "keys":["a","b"]}`
`/merge`	Deep merge two objects	`{"a":{...}, "b":{...}}`
`/groupby`	Group array by field	`{"input":[...], "key":"field"}`
`/sortby`	Sort array by field (prefix - for desc)	`{"input":[...], "key":"-age"}`
`/size`	Size report with top keys breakdown	Raw JSON
`/security`	Scan for secrets, tokens, keys, IPs	Raw JSON
`/stats`	Count objects, arrays, keys, types, depth	Raw JSON
`/profile`	Data profiling (types, ranges, nulls per path)	Raw JSON
`/mock`	Generate realistic mock data from template	Raw JSON

Example

curl -X POST https://api.jsonfmt.dev/redact \
  -H "Content-Type: application/json" \
  -d '{"user":"Alice","password":"s3cret","api_key":"abc123"}'

Response:

{
  "user": "Alice",
  "password": "[REDACTED]",
  "api_key": "[REDACTED]"
}

Advanced Endpoints

Endpoint	Description	Body Format
`/jwt/decode`	Decode JWT token (header + payload)	Raw JWT string
`/schema/validate`	Validate JSON against Draft-07 schema	`{"data":{...}, "schema":{...}}`
`/schema/generate`	Generate JSON Schema from sample	Raw JSON
`/jsonpath`	JSONPath query (wildcards, filters, slices)	`{"input":{...}, "path":"$.x"}`
`/jsonl/validate`	Validate JSONL (one JSON per line)	Raw JSONL text
`/jsonl/to-array`	Convert JSONL to JSON array	Raw JSONL text
`/jsonl/from-array`	Convert JSON array to JSONL	Raw JSON array
`/patch`	Generate RFC 6902 JSON Patch	`{"a":{...}, "b":{...}}`

Example — JSONPath Query

curl -X POST https://api.jsonfmt.dev/jsonpath \
  -H "Content-Type: application/json" \
  -d '{"input":{"store":{"books":[{"title":"A"},{"title":"B"}]}},"path":"$.store.books[*].title"}'

Response:

{ "count": 2, "results": ["A", "B"] }

Error Codes

All errors return JSON with an "error" field.

{ "error": "description of what went wrong" }

Code	Meaning	How to Fix
`400`	Bad Request	Check your JSON syntax or request body
`401`	Unauthorized	Verify your API key is valid
`405`	Method Not Allowed	Use POST for processing endpoints, GET for /health
`429`	Rate Limited	Wait 60s or get an API key for higher limits
`500`	Server Error	Retry or contact support

Rate Limits

Rate limits are enforced per IP (anonymous) or per key (authenticated). Every response includes rate limit headers.

Tier	Rate Limit	Monthly Quota	Cost
Anonymous	10 req/min	Unlimited	Free
Free (with key)	100 req/min	1,000 requests	Free
Pro (with key)	1,000 req/min	50,000 requests	$9/mo

Pricing

Anonymous

No sign-up required

10 requests / minute
All endpoints
No monthly limit
Community support

Free

With API key

100 requests / minute
All endpoints
1,000 requests / month
Email support

Pro

$9 lifetime

Pay once, Pro forever

1,000 requests / minute
All endpoints
50,000 requests / month
Priority support

Get Your API Key

Get a free API key in 3 steps. We will send a 6-digit verification code to your email.

1Enter email

2Verify code

3Your key

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Test Your API Key

Paste your API key to check your tier, rate limits, and make a test request.

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jsonfmt.dev · support@jsonfmt.dev · GitHub