How to Host a Tableau Viz Extension, from Local to Cloud

The .trex is XML. The top tags identify the extension (a reverse-domain id, version, name, description, author), but none of that runs anything. The one element Tableau really depends on is the source location URL, which tells Desktop where the actual web files are.

For a viz extension, the manifest also defines the Marks card. The encodings you declare replace the usual Color, Size, Detail and Tooltip slots, and the web code uses those ids to read what the user drops on them. In the demo Sankey, that means Source, Target and Value.

The local .trex points at localhost on port 9999, with index.html as the root file. Once the extension is allowed, Eric's build shows a custom splash screen asking for a dimension on Source, a dimension on Target and a measure on Value. Without one, he expects you just get a blank canvas.

The splash logic watches the encodings, so the message can change as fields arrive, for example telling the user they still need Target and Value. The chart itself is drawn by the HTML and JavaScript, rendered by Tableau in something like an iframe, with the Tableau Extensions API library packaged alongside as a requirement.

Eric runs his local server with Python: open a terminal in the root folder where index.html sits and run python -m http.server followed by the port. The port has to match the one in the .trex. He stops any other server first so they do not compete.

To take Tableau out of the equation, go to localhost and the port in a browser. You should not see errors there. Many extensions are not built to run outside Tableau and will say they cannot find Tableau, which is expected. If the files sit in a subfolder, you have to start the server from that folder instead, and relative paths like the library reference have to still resolve.

If you change only the web files, re-selecting the already loaded extension from the dropdown refreshes it with your changes. If the local server is stopped, you get an error message, unless the build happens to be self-contained, which is why Eric's demo kept rendering after he shut the server down.

Changes to the .trex itself are different. The manifest is cached in the workbook, so after Eric comments out the Source encoding nothing changes until he adds the extension again as a new one. Repointing a .trex works the same way.

A workbook using a localhost .trex publishes fine and then fails to render. On Server, if you have access to the VM, you can run the same small local server on the machine running Tableau Server. On Cloud, or without that access, the web files have to be hosted somewhere Cloud can reach.

That can be wide open, like a public S3 bucket or Cloudflare, or locked down to the Tableau Cloud IP addresses. The Tableau Exchange is the third option: those extensions are hosted files running on a server somewhere. In Q&A, Eric adds that hosting extensions adds no new Bridge requirement.

Eric keeps a second .trex with hosted in the name. The only difference is the URL. He uploads the root folder to ext.tableauops.com, his own hosting platform, which checks for the files an extension requires and shows a preview. It gives back the URL of the folder holding index.html, and he pastes that into the hosted .trex.

Because each .trex acts as its own extension, he then adds it as a new extension in the workbook, clears a cached version, confirms the extension URL now shows the hosted address, and republishes so the workbook picks up the change. He built in a label showing whether the local or hosted version is connected, which makes this easy to check.

Even with the files hosted and the workbook republished, Cloud still errors until the host is safelisted. An admin goes to Settings, then the Extensions tab, and adds the same URL that is in the .trex. A wildcard works too, with a slightly unusual syntax: a period then a star.

The same settings page controls the prompt asking users to allow the extension. By default it appears every time the workbook loads, even for users who already accepted. Setting it to hide removes it, and on reload the extension renders with no prompt.

Granting an extension access to the data does not mean the data goes anywhere. But with a bad actor behind it, JavaScript could siphon data off the data source. Eric says the Exchange helps because Tableau certifies some partners, such as LA Data Viz, though not every Exchange extension has that certification.

That risk is part of why he wanted local and self-hosted options: if you host the files yourself, you are not depending on an outside third-party developer you do not know.