I downloaded vue-loader-example and installed Vue Devtools extension for Chrome. I can get the example working by running npm run dev. The problem is that I don't see the Vue Devtools tab on my Chrome devtools.
I'm running Chrome version 46.0.2490.86 on my Macbook Pro.

Happened to me, although it was working yesterday. Reinstalled the extension and restarted chrome seems to have brought the tab back.
This is because you are opening the wrapped page served by webpack-dev-server, which in turn loads the actual app in an iframe.
Just go to localhost:8080 directly without the /webpack-dev-server path.
i have an same question,does it means vue-devtools cannot work with iframe?
you need use development (non-minified) versions of Vue. use vue.js, not vue.min.js.
https://github.com/vuejs/vue-devtools#notes
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Happened to me, although it was working yesterday. Reinstalled the extension and restarted chrome seems to have brought the tab back.