How to Find Every Unused Field in a Tableau Workbook (AI Extension Build)

Eric wanted X-Ray to analyze the workbook it is embedded in automatically. It can't. The dashboard extension API has no information about the workbook's file location or the system it runs on, so the first step is always selecting the workbook.

Once it has the file, the analysis is fast. The finished version shows an overview with warnings for developers, a calculated fields tab (42 calcs in his example), unused fields, lineage, orphan sheets, and a little data source detail, here a hyper extract.

Every extension Eric built used to walk through the same progression of errors from a fresh start. He wrote a skill specific to Tableau extensions to handle those common issues, and Michael, who has been testing it, reports the same.

It still doesn't catch everything. Prompt 0 looked for a starter folder that wasn't in the project, and loading the first .trex threw an error Eric doesn't usually see. His response is to tell Claude to add the fix to the skill so the next build doesn't hit it.

To load a dashboard extension, drag the Extension object onto a dashboard and choose Access Local Extensions. What Claude outputs is a .trex file, sometimes called the manifest. It is a small XML file with author, description and version details, plus the URL where the extension's web files are served.

Eric usually keeps two .trex files per extension, one pointing at the public host and one at localhost. The .trex points to index.html, and index.html loads the JavaScript and styles that do the work. In this case you could open that index file in a browser and get the same page.

A .twbx is a .twb and a hyper file zipped together. Prompt 1 has the extension unzip it, keep the .twb and drop the hyper. Eric notes this also helps when you keep workbook versions in a repository, because you avoid saving the data again with every iteration.

All of the opening and parsing happens in the extension's web files, then shows up as a web page inside the workbook. Tableau itself is not opening the workbook for it.

Prompt 3 flags a field as unused when no worksheet uses it and no calculated field depends on it. In the example that is 371 fields, which would bring the workbook under 100 used fields. Four of the 42 calculated fields are also unused.

Eric's understanding is that hiding a field removes it from the query sent to a live source or a hyper, so unused fields cost you until they are hidden. Better still is rewriting the source SQL to include only the fields you use. He also points out that fields on orphan sheets still count as used, so deleting those sheets can free more fields.

Prompt 4 adds a lineage tab that includes sheets as well as fields. Pick LOS days and it shows that LOS P12 and LOS T12 reference it and that it sits on four worksheets, so changing it would hit all of those.

Eric is honest about the rough edges. The tree reads in the opposite direction from what he wants (he'd put the base field at the top), it needs a tree navigator to climb back up, and he'd add an impact score for how many downstream objects a field touches.

Eric started a new chat for the live prompt on purpose. Anthropic's usage page now breaks out more detail, and it showed that 60 to 65 percent of his usage came from high context prompts, because he tended to run one chat forever.

Now he starts a new chat for each new idea, and he says that brought the number down. He adds that a recent VS Code update coordinates Claude chats within a session, which makes shorter chats easier.

The live prompt added a cleanup section on the unused tab. The extension explains it cannot edit the workbook you have open because the Extensions API is read-only, so the buttons rewrite the workbook XML and download a clean copy. You can pick which fields to hide and which sheets to drop. Eric ran both: 373 fields hidden and five sheets deleted.

Verifying it showed what still needs work. The orphan sheets were gone. The fields were tagged as hidden but still listed as unused, so the tool needs to explain unused versus hidden more clearly. Eric's advice on XML edits: keep a lot of backups, because the XML is touchy.