PHP compatibility checker online, or on your own server? What to know first
Short answer
An online checker needs your code: you paste it, upload it, or let it read your site from outside. That sends plugin and theme code, which may include licence checks, settings or a client’s custom work, to someone else’s server, and it only checks what you gave it. A checker that runs on your own server, inside WordPress, sees every plugin and theme as installed, sends nothing anywhere, and can tell you which files it couldn’t check. For client sites, that’s usually the safer choice.
What an online checker needs from you
An online PHP compatibility checker can only check code it has. So you paste a file, upload a plugin as a zip, or connect your site. Each way, your code leaves your server. That raises three questions worth answering before you click:
- Whose code is it? Premium plugins and themes are usually licensed for your use. Custom code may belong to your client.
- What’s in it? Plugin files can contain licence checks, connection settings or business logic.
- What does the service keep, and for how long? Read its terms.
A site checked from the outside, by address only, is a different thing: from outside, a checker sees the pages your site sends to visitors, not the PHP code of your plugins.
What it can’t see
An uploaded file is checked on its own. It doesn’t know which PHP version your site runs today, which plugins are active, or whether a problem is in code that never runs on your site. You end up checking plugins one by one and adding up the results yourself.
On your own server instead
A checker that runs inside WordPress has none of these problems: it reads every plugin and theme where they are installed, knows the PHP version the site runs, and sees which ones are active. Nothing needs to leave the server.
That is how the free CompatNav plugin works:
- Runs entirely on your own server. No code, file names or results are sent anywhere; it makes no external requests.
- Read-only. It never runs or changes the code it checks.
- Stores only scan results (file paths, line numbers, check IDs), never personal data.
- Sees the whole site: every plugin and theme, active or not, compared with the PHP version the site runs today. What a good checker does lists the rest.
When you do want to share the result, with a client or a developer, you download the report yourself: a self-contained HTML file that opens in any browser and prints to PDF, or a CSV. You decide who gets it.
For agencies
Client sites make the question sharper: their code, their data, your responsibility. A check that runs on each site’s own server keeps you out of that discussion. How to fit it into your routine: the maintenance checklist.
Key takeaways
- An online checker only sees the code you send it, and that code leaves your server.
- Plugin and theme files can contain things you shouldn’t share: licence logic, settings, a client’s custom work.
- A check inside WordPress sees every plugin and theme exactly as installed, including the inactive ones.
- Ask any checker: what does it send, where, and what does it store?
- The free CompatNav plugin runs entirely on your server: no code, file names or results are sent anywhere.
Frequently asked questions
Is it safe to upload plugin code to an online PHP checker?
It depends on the code and the service. Premium plugins are usually licensed to you, not to share; custom code may belong to your client. Read the service’s privacy terms, or check on your own server instead.
Can an online checker scan my live site?
From outside, it can only see what the site sends to visitors: pages, not the PHP code of your plugins. Checking plugin code needs access to the files.
Does CompatNav send anything to its makers?
No. The free plugin makes no external requests: no code, file names or results leave your site. It stores only scan results (file paths, line numbers, check IDs), never personal data.
Check your own site before you upgrade
CompatNav is a free WordPress plugin. It reads the code of your plugins and themes on your own server and tells you, in plain words, what will break and what will only show notices on the PHP version you choose. It never changes your code. It can’t see problems that only appear while code runs with real data, so a quick check of your site after the upgrade still matters.
Sources
About the code examples: each output is the real output of the code shown, run with the official PHP builds, without a php.ini, with all errors reported and displayed. Only the file path was replaced by a neutral server path.