Your content model belongs in a pull request.

{ "collections": [  { "slug": "posts", "fields": [-   { "name": "title",+   { "name": "headline",      "type": "text", "required": true },    { "name": "published", "type": "checkbox" }  ] }] }

$ tachyon schema diff schema.json~ change posts: remove title, deleting its data; add headline (text)  2 of 2 documents won't validate against the new fields  users isn't in the file; left as it is $ tachyon schema diff schema.json --rename posts:title=headline~ change posts: rename title to headline  users isn't in the file; left as it is $ tachyon schema apply schema.json --rename posts:title=headline~ change posts: rename title to headline  users isn't in the file; left as it is Applied.

Three commands

tachyon schema export -o schema.json
tachyon schema diff schema.json
tachyon schema apply schema.json

Export writes every content type to one file. Edit it, commit it, and the review happens where the rest of your code gets reviewed. diff tells you what applying it would do to the server in front of you, and apply does it. Collections the file doesn’t mention are left exactly as they are.

A rename isn’t a delete and an add

Rename title to headline and a naive tool sees one field leave and another arrive, and your titles leave with the old one. Here, diff tells you plainly that it would delete data. Add --rename posts:title=headline and every document keeps its title under the new name. Nested fields work the same way: posts:seo.title=headline.

Destructive changes ask first

The same safety holds over the API. Send a changed schema to PUT /api/admin/collections/posts, with any renames beside it, and anything that would delete or retype data comes back first as a preview: what changes, how many documents it touches and which ones won’t validate. It only goes through when you send it again with "confirm": true. POST /api/admin/collections/posts/preview shows the same report and changes nothing.

Rules travel with it

Access rules are part of the schema, so they export, diff and apply with everything else. A file that would break a rule somewhere else, say by removing a profile field that another collection’s rule reads as $user.team, is refused before anything changes.