Dummy JSON File Generator
Every dummy JSON file is valid JSON with a records array, filled to the exact byte size you set.
Sample JSON files, ready to download:
One click, exact size (1 KB = 1,024 bytes), default options, built in your browser.
A dummy JSON file is valid, pretty-printed JSON made for testing: a meta object and an array of user-like records. Download one free at the exact size you need, from 256 Bytes to 50 MB. Use it to test API request limits, JSON parsers, import scripts and message queues without pasting production data into a test. If your data is flat rows rather than objects, a dummy CSV file is the better fit.
How we check it: every generated file must be exactly the size you set and pass JSON.parse; the last run on 21 October 2026 passed 155 of 155 runs across 17 formats (how the files are made and checked).
What is inside a dummy JSON file
The structure is fixed, so you know what your parser will see (how we build and check these files):
- A top-level object with two keys: meta (generator, title, targetSizeBytes and generatedAt) and records.
- records is an array of objects with id, name, email, active and role. The first three are Alice Smith, Bob Jones and Carol White; after that come User 4, User 5 and so on, with emails like user4@example.com. Ids count up from 1.
- Two-space indentation, UTF-8 without a byte order mark, LF line endings.
- A bigger size means more records. The few bytes that do not fit a whole record (about 150 at most) are spaces before the closing bracket, which JSON allows.
What a dummy JSON file is used for
API payload limits
Post the file as a request body and find the exact size where your API, proxy or framework starts answering 413.
Parser and memory tests
Load 1 MB and 50 MB versions and watch memory. Parsers that read everything at once grow with the file; streaming parsers do not.
Import and seed scripts
Feed predictable records with sequential ids to import jobs and check counts, duplicates and error handling.
Queues and logs
Send large JSON messages through queues, webhooks and log shippers that have their own size caps.
Testing a JSON request size limit
APIs usually limit the request body, not a file. Send the dummy JSON as the body with Content-Type: application/json at one byte under, at and over the limit. Express is a good example: its JSON body parser defaults to a 100 KB limit and answers 413 above it, which surprises a lot of people the first time a real payload crosses that line.
If the JSON travels inside something else, count the wrapper too. Base64 makes data about a third bigger, so a 75 KB file becomes roughly 100 KB on the wire.
| Limit | Size | Notes |
|---|---|---|
| nginx client_max_body_size (default) | 1 MB 1,048,576 B | Requests with a larger body get HTTP 413. |
| PHP upload_max_filesize (default) | 2 MB 2,097,152 B | Also capped by post_max_size, so raise both. |
| AWS Lambda synchronous invocation payload | 6 MB 6,291,456 B | Applies to request and response. |
| Amazon API Gateway REST API payload | 10 MB 10,485,760 B | Hard quota for REST APIs. |
| Outlook default attachment limit (Exchange accounts) | 10 MB 10,485,760 B | Administrators can change it. |
| Outlook attachment limit (internet accounts) | 20 MB 20,971,520 B | Per Microsoft Outlook guidance. |
| Gmail message size limit | 25 MB 26,214,400 B | Attachments grow about a third when encoded, so a 20 MB file can already be too big. |
Posting the file with curl
curl -X POST -H "Content-Type: application/json" --data-binary @dummy-records.json https://your-api.example/endpoint
Use --data-binary, not -d. With -d and a file, curl strips the line breaks, so the body you send is smaller than the file you made.
JSON file details
- Extension
- JSON .json
- MIME type
- application/json
- Smallest size
- 256 Bytes
- Largest size
- 50 MB
- Contents
- Valid JSON with a meta block and a records array; extra size adds records, the last few bytes are spaces
Dummy JSON file FAQ
Is the dummy JSON file valid?
Yes. It parses with JSON.parse, has no byte order mark and is valid UTF-8. Our checks also confirm the meta object, the records array and the sequential ids.
What does the JSON contain?
A meta object (generator, title, target size, creation time) and a records array of objects with id, name, email, active and role.
Can I choose the number of records?
Not directly. The number of records follows from the size: a bigger file holds more of them. Pick the size and the records fill it.
How is the exact file size reached?
Whole records fill most of the file, and the last few bytes are spaces before the closing bracket. Whitespace is allowed there, so the file stays valid JSON.
Are the names and emails real?
No. They are made up, and every email uses example.com, a domain reserved for documentation and tests.
Is my data sent anywhere?
No. The JSON is created in your browser and never uploaded.