Diffing with LLM Analysis

cmx diff shows how an installed artifact differs from its source — directionally, so you can see which copy holds which change and pick the right way to reconcile.

cmx agent diff python-craftsperson
cmx skill diff personal-finance

If every installed copy is byte-identical to the source, cmx reports "matches" without calling the LLM. (The diff command requires a build with the llm feature; a lean build doesn't include it.)

What you get

The output names both sides with their real names — the source (home, or the repo) and the platform whose copy is shown (e.g. codex) — and uses them consistently, so you never have to map "installed"/"source" onto an actual copy. It stays compact by default:

a header naming each side, its path and version, and flagging the installed copy as edited locally when its bytes no longer match the lock baseline;
a per-file change summary — M modified (with +added −removed counts), A added (only in the installed copy), D deleted (only in the source) — under a stated convention: − lines are the source, + lines are the installed copy;
an LLM summary of what changed and which direction it recommends;
a reconcile footer offering both directions and picking neither.

The full line-by-line unified diff prints only with --full (a one-line hint points there), so a large change reads in ~20 lines instead of hundreds:

cmx skill diff personal-finance --full

Example output

Comparing personal-finance (skill) vs home

  codex   ~/.agents/skills/personal-finance                       (1.3.0, edited locally)
  home    ~/.config/context-mixer/home/skills/personal-finance    (1.3.0)

− lines are home, + lines are codex:

Changed files:
  M  SKILL.md                                    +12  −3
  A  helpers/categorize.py                       only in codex

Summary:
The installed copy adds a categorisation helper and tightens the SKILL.md
trigger wording. Behavioural addition, not a fix — keep it if the edits are
yours.

Reconcile — pick a direction:
  keep codex's edits — copy codex into home          cmx skill promote personal-finance
  discard codex's edits — pull home over codex       cmx skill update personal-finance --force
      (overwrites your local edits)

(run with --full to see the line-by-line diff)

The two reconcile directions map to two commands: promote keeps the installed edits by copying them into the home (offered when the source is the home — see Promoting Local Edits), and update --force discards them by pulling the source over the installed copy. diff recommends a direction but commits to neither.

Multi-platform aware

diff agrees with cmx doctor: it surveys every installed copy of a skill across your managed platforms, not just the active one. When more than one copy exists it shows a per-platform matrix — which copies match the source, which differ — and focuses the detailed diff on a copy that actually differs, so it never reports "matches home" while another platform's copy has drifted:

  claude   ~/.claude/skills/personal-finance     matches home
  codex    ~/.agents/skills/personal-finance     differs from home (+12 −3)   ← detailed below

The reconcile commands are qualified with --platform for the focused copy (preferring a managed platform, e.g. --platform codex over opencode), and a fully-consistent skill reports "matches home on all N installed copies". Agents stay single-copy — they're reformatted per platform (e.g. Codex TOML), so a byte-level cross-platform comparison isn't meaningful.

Works with untracked artifacts

diff works on any installed artifact that has a matching source — even ones not tracked in the lock file. It finds the file on disk and compares directly.

LLM configuration