There kind of is - there’s the extensions API. Extensions can add new tabs to the existing devtools (eg redux-devtools, react-devtools do this). Plus you could

There kind of is - there’s the extensions API. Extensions can add new tabs to the existing devtools (eg redux-devtools, react-devtools do this). Plus you could conceivably use content scripts and an extension page running in a popup window to make a whole alternative ‘devtools’ (which is roughly how Firebug worked). I imagine you wouldn’t be able to do anything like the Network tab though, as I don’t think extensions can monitor requests, and almost certainly can’t do things like throttling bandwidth etc. Thinking about it, I guess there’s quite a lot that modern devtools does you couldn’t do with an extension.