Diff MCP App (Next.js + Firestore)

This is an MVP Diff App + MCP "diff service" with local document storage.

• Humans resolve diffs in the UI.
• Codex (or any client) creates sessions and pulls resolutions via MCP.
• Session state is stored in local JSON files.

Features (v1)

• Batch + session creation from a manifest (src/target strings included)
• Monaco-based diff view
• Resolutions stored as resolvedText with status transitions:
  • PENDING -> RESOLVED -> APPLIED
• MCP API tools:
  • diff.create_sessions
  • diff.get_batch_status
  • diff.list_sessions
  • diff.get_resolved
  • diff.mark_applied

Environment variables

Create a .env.local (for local dev) or set these in Vercel:

Required:

• DIFF_DATA_DIR (optional) : service account JSON string (minimally contains project_id, client_email, private_key)
• DIFF_MCP_TOKEN : bearer token used to protect /api/mcp

Optional:

• APP_BASE_URL : public base URL (e.g. https://your-app.vercel.app). If not set, it is derived from request headers.
• DIFF_UI_TOKEN : if set, UI API endpoints require x-ui-token: <DIFF_UI_TOKEN>
• NEXT_PUBLIC_APP_BASE_URL : if set, UI pages use it when server-side fetching (handy for some deployments). Usually can be omitted.

See .env.example.

Local development

npm install
npm run dev

MCP endpoint

POST /api/mcp

Headers:

• Authorization: Bearer <DIFF_MCP_TOKEN>

Body:

{ "tool": "diff.create_sessions", "args": { "source": { "commit": "..." }, "items": [ ... ] } }

Local storage

• .data/batches.json
• .data/sessions.json

Notes

• The app stores src_description, target_description, and resolvedText in local JSON. If you want to reduce breach impact, the next step is application-level encryption of these text fields.