As part of our work on Endings, Martin Holmes and Joey Takeda have created two collections of software which are open-source on GitHub.
This codebase provides a pure-JSON search engine for your HTML5 website, including boolean and phrasal searches, various types of search filter, keyword-in-context results, and bookmarkable search results. It uses no back-end code at all, so it complies with Endings principles. Take a look at the Mapping Keats’s Progress site search for a working example.
This codebase is a toolkit for checking the coherence, consistency and completeness of your TEI XML project from inside the Oxygen XML Editor (although you can also use it at the command line). It performs a number of generic checks through the collection, but it is also easily extensible to check other features that may be particular to your project.
A similar toolkit is available to check your HTML.