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seampact

Diff a contract change

Use seampact diff to see what a contract edit breaks before you ship it. A change is additive if existing clients still work, and breaking if one can fail. Run the commands in the app folder. Without Node, run it with the compiler binary: see commands per stack. The lines below use npx for Node.

Save the current contract as a baseline, then edit the contract.

Terminal window
npx seampact compile --out baseline

The baseline folder is regenerated by compile: add it to .gitignore. In CI, take the baseline from your main branch: see Sharing a contract.

Add author to CreateNote: required: [title, author] and author: { type: string } under properties. Then compare.

Terminal window
npx seampact diff --against baseline

You see breaking clients createNote input ...: property.added required (author). Existing clients do not send author.

By default diff reports. With compat: { policy: additive-only } under api: it fails (exit 1) on a breaking change. By default only breaking changes for clients fail; change this with diff.gate. Breaking changes on experimental routes do not fail (diff.exempt).

Undo the demo edit (remove author) so the next page’s check starts clean.

Next

Section titled “Next”

check in CI.