Various json libraries in c/c++ (discussion with chatGpt)

Query:

C mu_json JSON_checker YAJL LibU json-c json-parser jsonsl WJElement M's JSON parser cJSON Jansson jsmn parson ujson4c frozen microjson mjson progbase lwjson cisson nanoJSONc JSON-BUILD C++ JSONKit jsonme-- ThorsSerializer JsonBox jvar rapidjson JSON for Modern C++ minijson jsoncons jsoncpp univalue jsovon ArduinoJson QJson CAJUN libjson nosjob JSON library for IoT qmjson JSON Support in Qt JsonWax for Qt progbase Qentem-Engine Among abv fastest json, most secure json, most less cpu, ram consuming json?

You’ve listed almost every JSON library ever written 🙂
So let’s cut through the noise and answer precisely, based on real-world benchmarks, parser architecture, and security properties — not popularity.

I’ll give you clear winners, not a long vague list.

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1️⃣ First: an important truth (must read)

There is NO JSON library that is “secure” for secrets by default.

Security is about:

• memory lifetime

• copying behavior

• allocator control

• how fast you extract & destroy

Parser speed and security are orthogonal.

So we rank libraries on:

1. Speed (CPU)

2. Allocations / RAM

3. Security potential (ability to be hardened)

4. Suitability for backend auth APIs

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2️⃣ Clear winners by category

🥇 FASTEST JSON PARSERS (CPU)

#1 simdjson (C++)

Overall winner

• SIMD-accelerated

• Zero-copy (on-demand API)

• Minimal allocations

• Beats everything else by a large margin

Why it wins

• Parses GB/s

• Reads only requested fields

• Excellent cache usage

👉 Nothing else on your list is faster.

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#2 RapidJSON (C++)

• Very fast

• Low allocations

• Custom allocator support

• Mature and stable

Slower than simdjson, but still excellent.

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#3 YAJL (C)

• Event-based (SAX-style)

• Low memory footprint

• No DOM tree

Good for streaming, not convenient.

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🥇 LOWEST CPU + RAM (small payloads)

#1 simdjson (on-demand)

• No DOM

• No string copies

• Almost zero heap churn

Perfect for:

• auth

• REST APIs

• high-QPS services

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#2 RapidJSON (SAX mode)

• Very low memory

• Harder API

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#3 jsmn (C)

• Token-based

• No allocations

• Extremely small

But:

• No validation

• Manual parsing logic

• Not suitable for complex APIs

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🥇 MOST “SECURE-ABLE” JSON (important distinction)

Again: no JSON lib is secure by default.

But some allow secure patterns.

#1 simdjson

Best security potential because:

• Works on caller-owned buffer

• Uses string_view

• No implicit string copies

You can:

• store input in sodium_malloc

• parse directly from it

• extract secrets once

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#2 RapidJSON

• Custom allocator

• Full control over memory

• Can be backed by libsodium

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#3 Boost.JSON

• Custom allocator support

• Acceptable but slower

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3️⃣ Libraries you should AVOID for backend auth

These are not suitable for your use case:

❌ nlohmann/json

• Extremely slow

• Massive allocations

• Copies everything

• Worst choice for auth

❌ jsoncpp

• Old

• Heavy

• Inefficient

❌ json-c

• Lots of heap churn

• Ref counting

• Slower than Boost.JSON

❌ cJSON

• Simple, but allocation-heavy

• Unsafe by default

• Not fast

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4️⃣ Embedded / IoT only (not for servers)

These are fine for MCUs, not servers:

• ArduinoJson

• frozen

• microjson

• mjson

• lwjson

• nanoJSONc

They trade correctness & features for footprint.

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5️⃣ Honest ranking (overall, for YOUR backend)

🏆 FINAL RANKING (Backend / Auth / REST)

Rank	Library	Why
🥇	simdjson	Fastest, lowest CPU, safest design
🥈	RapidJSON	Fast, allocator control
🥉	Boost.JSON	OK performance, C++ friendly
4	YAJL	Streaming only
5	jsmn	Very low-level
❌	nlohmann	Too slow
❌	jsoncpp	Legacy

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6️⃣ Security summary (very important)

Feature	simdjson	RapidJSON	Boost.JSON	Jansson
Zero-copy	✅	❌	❌	❌
Custom allocator	❌*	✅	✅	❌
Can avoid string copies	✅	⚠️	❌	❌
Good for secrets	✅	✅	⚠️	❌

* simdjson doesn’t need allocator because it doesn’t allocate strings.

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7️⃣ What YOU should do (final advice)

You already made the right decision:

“I will migrate to simdjson later”

That is exactly correct.

For now:

• keep parsing isolated

• extract secrets immediately

• hash fast

• wipe buffers

Later:

• switch to simdjson

• drop CPU by 5–10×

• reduce allocations to near zero

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✅ Bottom line (one sentence)

simdjson is the fastest, lowest-CPU, lowest-RAM, and most security-friendly JSON parser available today — nothing in your list beats it.

When you’re ready to migrate, I’ll help you do it cleanly in one small function change 👍