<p>You're likely missing the PHP <a href="https://php.net/manual/en/book.json.php" rel="nofollow">JSON extension</a>, which is a <a href="http://buildwithcraft.com/docs/requirements#required-php-extensions" rel="nofollow">requirement</a> to run Craft.</p>

CC BY-SA 3.0
2015-04-26T20:18:57.723Z
2015-04-26T20:18:57.723Z
Brad Bell
<p>I'm running PHP 5.3.3, which the docs say is supported, but if I try to go to the main admin page or go to add a field, I'm getting an error: 
    Use of undefined constant JSON_HEX_TAG - assumed 'JSON_HEX_TAG'</p>

<p>Everything I'm finding online points to this being an outdated PHP issue, but thought I would check since I am running a supported version of PHP. </p>

<p>Thanks!</p>

<error-message><php><json>
Use of undefined constant JSON_HEX_TAG
# Use of undefined constant JSON_HEX_TAG

(Asked by: username_0 on 2015-04-26)

I'm running PHP 5.3.3, which the docs say is supported, but if I try to go to the main admin page or go to add a field, I'm getting an error:
Use of undefined constant JSON\_HEX\_TAG - assumed 'JSON\_HEX\_TAG'

Everything I'm finding online points to this being an outdated PHP issue, but thought I would check since I am running a supported version of PHP.

Thanks!

**Tags:** error-message, php, json


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## 1 answers

### Answer by username_1 on 2015-04-26. Score: 4 | Accepted answer

You're likely missing the PHP [JSON extension](https://php.net/manual/en/book.json.php), which is a [requirement](http://buildwithcraft.com/docs/requirements#required-php-extensions) to run Craft.


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