<p>Well:</p>

<pre><code>stringdist::stringdist("rjson", "jsonlite")
## [1] 5
</code></pre>

<p>That's a modest difference to begin with.</p>

<p>However, your assertion seems to be amiss:</p>

<pre><code>library(magrittr)

rjson::fromJSON('{"name": "Sanjay",
"unit_price": 130848,
"amount": 11,
"up_to_data_sales": 45725}') %&gt;% str()
## List of 4
##  $ name            : chr "Sanjay"
##  $ unit_price      : num 130848
##  $ amount          : num 11
##  $ up_to_data_sales: num 45725

jsonlite::fromJSON('{"name": "Sanjay",
"unit_price": 130848,
"amount": 11,
"up_to_data_sales": 45725}') %&gt;% str()
## List of 4
##  $ name            : chr "Sanjay"
##  $ unit_price      : int 130848
##  $ amount          : int 11
##  $ up_to_data_sales: int 45725
</code></pre>

<p>Apart from <code>jsonlite</code> using a more diminutive data type for the numbers, they both parse the JSON fine.</p>

<p>So there's an issue with your file that you failed to disclose in the question.</p>

<p>A further incorrect assertion </p>

<pre><code>-rw-rw-r--  1 bob  staff      2690 Jul 30  2007 rjson_0.1.0.tar.gz
-rw-rw-r--  1 bob  staff    400196 Dec  3  2013 jsonlite_0.9.0.tar.gz
</code></pre>

<p>not to mention:</p>

<pre><code>-rw-rw-r--  1 bob   staff   873843 Oct  4  2010 RJSONIO_0.3-1.tar.gz
</code></pre>

<p><code>rjson</code> came first. (dir listings came from the CRAN mirror sitting next to me).</p>

<p>You can <em>actually read</em> about the rationale and impetus behind <code>jsonlite</code> here: <a href="https://arxiv.org/abs/1403.2805" rel="nofollow noreferrer">https://arxiv.org/abs/1403.2805</a> (which I got off the CRAN page for <code>jsonlite</code>.</p>
what is the fundamental difference between jsonlite and rjson packages?
<p>The rjson::fromJSON() reads a file incorrectly while jsonlite::fromJSON() reads it fine. Here's a sample example.</p>

<p>file test.json contents:</p>

<pre><code>{"name": "Sanjay",
"unit_price": 130848,
"amount": 11,
"up_to_data_sales": 45725}
</code></pre>

<p>the <code>jsonlite</code> <code>fromJSON</code> outputs:</p>

<pre><code>jsonlite::fromJSON("test.json")
$name
[1] "Sanjay"

$unit_price
[1] 130848

$amount
[1] 11

$up_to_data_sales
[1] 45725
</code></pre>

<p>But the same throws an error in <code>rjson</code> package.</p>

<pre><code>rjson::fromJSON("test.json") 

Error in rjson::fromJSON("test.json") :   parseTrue: expected to see 'true' - likely an unquoted string starting with 't'.
</code></pre>

<ol>
<li>Why is this error coming?</li>
<li>What is the reason <code>rjson</code> package was launched when <code>jsonlite</code> existed?</li>
</ol>