JSON Size Calculator | Payload Size Checker

JSON size calculator that shows exact payload bytes minified, pretty, gzipped and base64, finds the heaviest keys and checks SQS, Lambda and DynamoDB limits.

Also known as: json size calculator · json payload size calculator · json size checker · json size analyzer · calculate json size in bytes · json file size in kb · api payload size calculator · json gzip size · json byte size online

json tools

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JSON Input

Size Breakdown

Exact byte sizes, gzip size, the biggest keys and paths, and a check against common payload limits will appear here.

About JSON Size Calculator

A JSON size calculator tells you how many bytes a payload really takes before it hits a limit you cannot raise, like a 256 KiB Step Functions state or a 400 KB DynamoDB item. Paste a document and it reports the exact UTF-8 size as pasted, minified, pretty-printed, gzipped and base64-encoded, then shows which keys and paths are spending those bytes.

Key Features

Exact UTF-8 byte counts for the input, minified and 2-space pretty-printed forms
Real gzip size measured with the browser's built-in CompressionStream
Largest paths ranked by bytes, with array items merged as [*] so repeated records add up
Bytes spent on key names, the number that shrinks when you shorten keys in big arrays
Checks against 12 published limits including SQS, SNS, Lambda, DynamoDB, Kafka and Vercel
Line and column for syntax errors, plus a warning for duplicate keys

Use Cases

Check that a webhook or API response stays under the 6 MB synchronous AWS Lambda limit
Find out why an SQS message or SNS notification is being rejected as too large
See whether a DynamoDB item is creeping toward 400 KB before writes start failing
Measure how much gzip saves on a REST response before turning on compression at the CDN
Find the one nested array that makes a mobile app's JSON payload heavy
Estimate the size of a Kafka message or Firestore document before you ship the schema

Supported Formats

JSON

API responses

.json files

UTF-8

Related Keywords

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Why is my JSON bigger than its character count?

Because limits are measured in bytes of UTF-8, not characters. Plain ASCII takes 1 byte per character, but an accented letter like é takes 2, most CJK characters take 3, and an emoji takes 4, so a payload full of names, addresses or emoji can be noticeably larger than its length in a text editor. Whitespace counts too: pretty-printing with two spaces often adds 20 to 40 percent to a nested document. Services such as SQS, SNS and DynamoDB measure the raw bytes they receive, so compare your minified size against their limits. Gzip helps on the wire to browsers and CDNs, but it does not raise a queue or database limit.

Privacy & Security

All processing happens locally in your browser. Your data never leaves your computer, ensuring complete privacy and security.

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Frequently asked questions

What is JSON Size Calculator used for?

JSON size calculator that shows exact payload bytes minified, pretty, gzipped and base64, finds the heaviest keys and checks SQS, Lambda and DynamoDB limits.

Is JSON Size Calculator free to use?

Yes. JSON Size Calculator is completely free with no usage limits, and there is no paid tier required to use it.

Do I need an account to use JSON Size Calculator?

No. JSON Size Calculator works immediately in your browser with no signup, login, or email address required.

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