yarn add postgraphile-db-inspector-extension

Use as a server plugin; e.g.

postgraphile --plugins postgraphile-db-inspector-extensions -c my_db

or

const pgdbi = require('postgraphile-db-inspector-extension')
const {postgraphile, makePluginHook} = require("postgraphile");
const pluginHook = makePluginHook([pgdbi]);

app.use(postgraphile(connectionString, schemas, {
  pluginHook,
  enablePgdbi: true
}))

In library mode you must enable pgdbi in PostGraphile options:

enablePgdbi: true,

You can access pgdbi at the /pgdbi sub path, e.g. http://localhost:5000/pgdbi.