JSON Size Calculator: Measure Payload Size Online
Overview
Large JSON payloads slow down API responses and mobile apps. Before optimizing, you need to know which fields are taking up the most space. This tool calculates total byte size, shows the top 10 largest keys by value size, and reports nesting depth and array lengths.
How to Use This Tool
Paste your JSON and click Analyze. The summary shows total size in bytes and KB, the deepest nesting level, the largest string values, and the count of keys and array items at each level.
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PDF Tool →Frequently Asked Questions
Why is my JSON payload so large?
The most common causes are embedded base64-encoded images or files, deeply nested objects with many repeated keys, and large arrays of objects with redundant fields per item.
How can I reduce JSON payload size?
Remove unused fields, shorten verbose key names, paginate large arrays instead of returning everything at once, and avoid embedding binary data as base64 in JSON.
Does this tool measure compressed or uncompressed size?
The size shown is the uncompressed byte count of the JSON text. HTTP gzip compression typically reduces JSON size by 60-80%, but you should measure uncompressed size when checking against API limits.