The EntitySchema extension, as deployed on https://wikidata-shex.wmflabs.org/, currently links to the shex-simple tool, or “ShEx2 – Simple Online Validator”, where users can check a set of Wikidata entities against the specified schema.
Despite its name, this tool is not simple. It’s grown into a highly powerful tool to check data from diverse sources, against schemas from diverse other sources, with multiple ways to specify the focus nodes, manifest support, multiple user interface styles, drag’n’drop support, and more. This is great for power-users, but overwhelming for Wikidata editors new to the ShEx world; we’ve tried to mitigate this to some extent (T218886 and subtasks), but we’re starting to hit the limits of how much the tool can be adapted for a rather different target audience without inconveniencing its original users.
Instead, we could try to build a separate tool, providing a straightforward path for the common Wikidata workflow: given a schema, provided via URL (Special:EntitySchemaText/ID), and a SPARQL query selecting focus nodes, entered by the user, check those nodes against the schema. One input field, one button, one output area, and that’s it.
The checking would still be done in-browser via the shex.js library, so on the server side this just needs to serve some static files (HTML, CSS, JS).