https://docsearch.algolia.com/
It's free!!!
Many softwares and websites are using Algolia as a search engine (paid service).
However, a service called DocSearch provides free service for tech blogs and documentation.
Regular algolia requires the author to upload data for indexing. DocSearch uses a web crawler to periodically scrape your site just like a real search engine.
There are requirements to meet in order to use DocSearch, [see details](https://docsearch.algolia.com/docs/who-can-apply#the-checklist)
1. Your website must be publicly available (no auth or private network).
2. Your website must be a technical documentation of an **open source** project or a **technical blog**.
3. Your website must be production ready (no empty websites nor placeholder).
To apply, you will need to provide the following information, [application](https://docsearch.algolia.com/apply/)
1. Website URL
2. Contact Email (code snippet will be sent)
3. Repository URL (to verify if your project is open-source)