--- name: gitnexus-impact-analysis description: "Use when the user wants to know what will break if they change something, or needs safety analysis before editing code. Examples: \"Is it safe to change X?\", \"What depends on this?\", \"What will break?\"" metadata: internal: true --- # Impact Analysis with GitNexus ## When to Use - "Is it safe to change this function?" - "What will break if I modify X?" - "Show me the blast radius" - "Who uses this code?" - Before making non-trivial code changes - Before committing — to understand what your changes affect ## Bind the repository first Impact analysis is the gate that authorizes an edit, so it must answer for the repository you are about to edit. Call `list_repos {}` before the first tool call. With one indexed repository, use the examples below as written. With more than one, pass `repo` on every call: an omitted `repo` normally errors, but under an MCP policy with a configured default it resolves to that default silently. If you cannot tell which repository is meant, stop and ask — every result below an ambiguous identity inherits the ambiguity. `list_repos` is paginated, so page with `offset: pagination.nextOffset` until `hasMore` is false before concluding a repository is absent. `detect_changes` takes `worktree` when your changes are in a linked worktree the MCP server was not launched from. The server auto-detects a worktree only when it was launched from inside one; otherwise `git diff` runs in the wrong checkout and reports zero changed symbols — a false clean check that carries none of the degradation flags described below. In the CLI fallbacks, `--repo .` means the current checkout; pass the intended repository path instead when you are not standing in it. State the bound identity with your risk report: ``` Repository: () Worktree: Index: , behind HEAD ``` ## Workflow ``` 0. list_repos {} → Bind repo (and worktree) 1. impact({target: "X", direction: "upstream"}) or `node .gitnexus/run.cjs impact "X" --direction upstream --repo .` 2. READ gitnexus://repo/{name}/processes → Check affected execution flows 3. detect_changes({scope: "all"}) or `node .gitnexus/run.cjs detect-changes --scope all --repo .` 4. Assess risk and report to user, echoing repo/worktree/index identity ``` > If "Index is stale" → run `node .gitnexus/run.cjs analyze` in terminal. > If `.gitnexus/run.cjs` is missing, replace `node .gitnexus/run.cjs` with `npx gitnexus` in the fallback commands. ## Checklist ``` - [ ] list_repos {} — bind repo; explicit repo when >1 indexed, ask if ambiguous - [ ] impact({target, direction: "upstream"}) or CLI fallback to find dependents - [ ] Review d=1 items first (these WILL BREAK) - [ ] Check high-confidence (>0.8) dependencies - [ ] READ processes to check affected execution flows - [ ] detect_changes({scope: "all"}) or CLI fallback for pre-commit check - [ ] Confirm the checkout you edited is the checkout that was diffed - [ ] Assess risk level and report, stating repo/worktree/index identity ``` ## Understanding Output | Depth | Risk Level | Meaning | | ----- | ---------------- | ------------------------ | | d=1 | **WILL BREAK** | Direct callers/importers | | d=2 | LIKELY AFFECTED | Indirect dependencies | | d=3 | MAY NEED TESTING | Transitive effects | ## Risk Assessment | Affected | Risk | | ------------------------------ | -------- | | <5 symbols, few processes | LOW | | 5-15 symbols, 2-5 processes | MEDIUM | | >15 symbols or many processes | HIGH | | Critical path (auth, payments) | CRITICAL | | **Zero callers found** | **UNKNOWN** | `UNKNOWN` is not a low rung on this scale — it means the walk could not answer. An empty caller set is equally consistent with "genuinely unused" and "the callers are not resolvable by the index" (plain-object property access, dynamic dispatch, cross-language calls), so few-callers ⇒ LOW does **not** apply. The result carries a `riskNote` saying so. Confirm with a text search before treating the symbol as safe to change or delete. `risk` is the edit gate: warn on HIGH/CRITICAL and stop on UNKNOWN until the uncertainty is resolved. Within single-repo mode, compare File and symbol targets with local `riskSharedAxes` (direct/total only). Within group mode, compare only group results: their `riskSharedAxes` overlays resolved cross-repo crossings on that local value. Never use either field to waive the edit gate. Check `riskScale.unusedAxes` before comparing kinds: MCP File walks omit process/module axes, while web Graph-RAG expands File targets to in-file symbols before enrichment. ## Tools **impact** — the primary tool for symbol blast radius. If MCP is unavailable, use `node .gitnexus/run.cjs impact --direction upstream --repo .` instead: ``` impact({ target: "validateUser", repo: "my-app", // required once >1 repository is indexed direction: "upstream", minConfidence: 0.8, maxDepth: 3 }) → d=1 (WILL BREAK): - loginHandler (src/auth/login.ts:42) [CALLS, 100%] - apiMiddleware (src/api/middleware.ts:15) [CALLS, 100%] → d=2 (LIKELY AFFECTED): - authRouter (src/routes/auth.ts:22) [CALLS, 95%] ``` **detect_changes** — git-diff based impact analysis. If MCP is unavailable, use `node .gitnexus/run.cjs detect-changes --scope all --repo .` instead: ``` detect_changes({scope: "all"}) → Changed: 5 symbols in 3 files → Affected: LoginFlow, TokenRefresh, APIMiddlewarePipeline → Risk: MEDIUM ``` Add `repo` once more than one repository is indexed, and `worktree: ""` when your changes are in a linked worktree the server was not launched from. `partial: true` (a graph query failed) or `truncated: true` (the changed-symbol listing was capped) means the result is short of the truth, and reads like `UNKNOWN` above: a zero there means unseen, not unaffected. Re-run it rather than tick the pre-commit check. A wrong-worktree zero carries neither flag and is shape-identical to a genuine clean result, so confirm the checkout you edited is the one that was diffed before treating an empty change set as a passed check. ## Example: "What breaks if I change validateUser?" ``` 0. list_repos {} → total: 2 (my-app, billing-api) — both define validateUser, so bind explicitly 1. impact({target: "validateUser", repo: "my-app", direction: "upstream"}) or `node .gitnexus/run.cjs impact "validateUser" --direction upstream --repo .` → d=1: loginHandler, apiMiddleware (WILL BREAK) → d=2: authRouter, sessionManager (LIKELY AFFECTED) 2. READ gitnexus://repo/my-app/processes → LoginFlow and TokenRefresh touch validateUser 3. Risk: 2 direct callers, 2 processes = MEDIUM Repository: my-app (/abs/path/my-app) Worktree: same Index: current ``` With a single indexed repository, step 0 returns `total: 1` and the `repo` argument drops out of every call above.