Frontend Frameworks

UltraJSON

A fast JSON decoder and encoder written in C with Python bindings.

Status
Generally available
Last checked
Checked · Oct 13, 2026
License
Open source
Pricing
Free tier · from $0
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What it is

UltraJSON is a high-performance library for encoding and decoding JSON data. It's designed to be faster than the standard Python json module, making it ideal for applications where speed is critical.

UltraJSON stands out for its speed and efficiency in JSON processing, making it a go-to choice for developers who need to optimize their application's performance without sacrificing Python's ease of integration.

When it fits — and when it doesn’t

A good fit for

  • Developers working on high-performance Python applications that require fast JSON parsing and generation.

  • Projects where the standard json module's speed is a bottleneck.

Look elsewhere if

  • Applications where ease of use is prioritized over performance, as UltraJSON requires more setup than the built-in json module.

  • Scenarios where compatibility with non-Python environments is necessary.

Known weaknesses

Each one links to the public issue, changelog or docs page it came from, where we have one.

  1. 01

    Limited language support

    UltraJSON is primarily a Python library with bindings in C, limiting its use outside the Python ecosystem.

  2. 02

    Does not handle complex JSON data structures well

    UltraJSON may struggle with deeply nested or large JSON objects, leading to potential performance degradation or errors.

  3. 03

    Lack of advanced features compared to other libraries

    UltraJSON focuses on speed and does not include additional features like pretty-printing, schema validation, or object hook functions available in more comprehensive JSON libraries.

What it does well

  • High performance JSON encoding and decoding

  • Written in C for speed

  • Python bindings for easy integration

Pricing

Free tier
YesOpen source — free to use
Paid from
$0
Model
Flat rate
Enterprise plan
No

Pricing not independently confirmed — check the vendor’s page.

Performance benchmarks

How Fast Is It?

Set up UltraJSON

Setup steps, common gotchas and what to check after 30 days.

Open the setup guide →
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