internal search engine

What sort of search terms are you looking at? Do your users need to search for certain parts or articles or something else?

I ask this because it is useless searching your site for some irrelevant term, it is not worth the effort.

To illustrate, here I search for a home with at least 4 bedrooms, priced below $450K.

In this case the content is stored in a JSON file. But this could be any relational database to your liking.

What I am trying to say with this, do not have a search box just for the sake of having a search box. It helps no one, least of all you as the developer.

Screaming Frog is a leading SEO/ Site auditing tool, try this here:

Is Screaming Frog a good choice? I have been using freefind...

By @default0vaokg78cv42

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Screaming Frog is not a search engine. 

It appears to be some kind of SEO auditing tool for developers. 

Now for a dose of reality.  Nothing worth having is free unless you want to manually build a custom site search with PHP & MySQL data. Of course, this requires your content be stored in an online database that can be queried.

https://riyoalo.medium.com/building-a-custom-search-engine-using-php-and-mysql-b9265a1693b2

Freefind.com is one I've used several times. The free version is OK but the paid version works very well -- much better than the free one.

Google custom search API is another option.  Pricing varies based on usage. Free for up to 100 searches per day,  (bots can easily chew that up if you're not careful).  After that you pay a nominal fee for 1,000 searches or more per day.  To use Google custom search API, first obtain a unique ID and API key from Google.  IMPORTANT: Keep your ID and key hidden from prying eye bots & harvesters.  They will exploit your account if given an opportunty.