Foremerge is an open-source coordination protocol for coding agents, built above Git. It lets agents keep isolated worktrees while sharing intent, semantic claims, dependencies, provisional Change Sets, decisions, validation, and provenance. Install by pasting one line into Claude Code, Codex, or Cursor. Every agent sees what others are about to change, even in separate worktrees.

Foremerge is a local "git like" coordination layer that sits above git. Before editing, each agent publishes an intent and the scopes it will change. The publish by the 2nd agent returns a HIGH destructive_vs_additive finding before writing any code. Agents keep their own worktrees and the shared state is one SQLite file in git's common directory. No hooks, no merge drivers, nothing rewrites your history.

It ships as one Rust binary with a CLI and MCP server with 18 tools. Because the protocol has nothing provider specific, a Claude agent and a Codex agent coordinate through the same store. Before any work is accepted, Foremerge runs a named check that you configured against the exact git state of the change.

Detection is deterministic, no judge model reading your code. HIGH conflicts are only asserted for declared operations. Claims are advisory leases, not locks. The open source version is single matching and not distributed consensus. Tested up to 98 parallel agents on the same repo with zero conflicts. Apache-2.0.