As long as your users are reasonably tech-saavy this is ok. But long URLs can be problematic when sent in email for many possible reasons, such as the email cl

As long as your users are reasonably tech-saavy this is ok. But long URLs can be problematic when sent in email for many possible reasons, such as the email client wrapping the URL and then creating a link out of just part of the original URL. The user sometimes doesn't realize this and gets unpredictable results when trying to use the URL they "saved" in the email. Perhaps instead, assuming the user is online, hash the json state data, then send the json+hash to the server and update the URL to URL?hash. Then the user has a much shorter URL, and the server can lookup the json state from the provided hash to resume the app at that state. As a bonus you then have versions of the data over time (either posted automatically in the background or on-demand when the user clicks Save).