JSON test files from 10 KB to 10 MB are available free. They hold array data containing Japanese text, so they exercise a structure close to a real API response.

Because JSON validity cannot be determined without parsing the entire document, the cost of "read it all just to validate" grows with file size. These files help you decide when to switch to a streaming parser.

Typical uses

Testing how a REST API handles a large response
Benchmarking JSON parsers and serialisers
Observing front-end behaviour when rendering a large dataset
Checking that nesting depth and large-integer precision survive intact

📖 Where people get stuck

JSON files from 10 KB to 100 MB, for checking API request-size limits and parser behaviour. The structure is deliberately simple. To try deep nesting or huge arrays, build those yourself with the caveats below in mind.

Case	What happens	What to do
Large integers lose their low digits	A JavaScript `Number` is a double, so integers are exact only up to 2⁵³−1. A 19-digit identifier is rounded silently.	Send identifier-like values as strings. Where the API cannot change, pull them out before numeric conversion using `BigInt` or a parser option.
A 100 MB JSON blows the memory limit	`json_decode()` and `JSON.parse()` materialise the whole document at once, and the resulting object is several times the size of the text.	Process large input element by element with a streaming parser. Often simpler operationally: cap the request size at the API and return `413` so the client splits it.
A duplicated key goes unnoticed	The JSON spec does not forbid duplicate keys, and most parsers silently keep the last one. A bug in the producer passes straight through.	Validate against a JSON Schema when the shape is known. To simply inspect the structure, formatting it with the JSON formatter and diffing is quicker.

You can put a charset on Content-Type: application/json, but the JSON spec makes UTF-8 the default. Some parsers reject UTF-16 or a leading BOM, so stripping the BOM before handing the text over avoids a class of incident.

📋 JSON files

About JSON files

Typical uses

Related reference and articles

📖 Where people get stuck