diff --git a/README.md b/README.md
index d012e11..3f1ddd4 100644
--- a/README.md
+++ b/README.md
@@ -1,39 +1,38 @@
 # Catalyst
 
-A self-hosted infrastructure registry. Track every VM, container, and service across your homelab — their state, stack, and which internal services are running on them.
+A self-hosted infrastructure registry for homelab Proxmox environments. Track virtual machines across stacks, monitor service health, and maintain a full audit log of every configuration change.
 
 ---
 
 ## Features
 
 - **Dashboard** — filterable, searchable instance list with state and stack badges
-- **Detail pages** — per-instance view with service flags, Tailscale IP, and timestamps
+- **Detail pages** — per-instance view with service flags, Tailscale IP, and a full change timeline
+- **Audit log** — every field change is recorded with before/after values and a timestamp
 - **Full CRUD** — add, edit, and delete instances via a clean modal interface
 - **Production safeguard** — only development instances can be deleted; production instances must be demoted first
-- **REST API** — every operation is a plain HTTP call; no magic, no framework lock-in
-- **Persistent storage** — SQLite database on a Docker named volume; survives restarts and upgrades
-- **Zero native dependencies** — SQLite via Node's built-in `node:sqlite`. No compilation, no binaries.
+- **Export / import** — JSON backup and restore via the settings modal
+- **REST API** — every operation is a plain HTTP call
+- **Persistent storage** — SQLite on a Docker named volume; survives restarts and upgrades
+- **Zero native dependencies** — SQLite via Node's built-in `node:sqlite`; no compilation, no binaries
 
 ---
 
 ## Quick start
 
-```bash
-docker run -d \
-  --name catalyst \
-  -p 3000:3000 \
-  -v catalyst-data:/app/data \
-  gitea.thewrightserver.net/josh/catalyst:latest
-```
-
-Or with the included Compose file:
-
 ```bash
 docker compose up -d
 ```
 
 Open [http://localhost:3000](http://localhost:3000).
 
+### Environment variables
+
+| Variable | Default | Description |
+|---|---|---|
+| `PORT` | `3000` | HTTP port the server binds to |
+| `DB_PATH` | `data/catalyst.db` | Path to the SQLite database file |
+
 ---
 
 ## REST API
@@ -44,13 +43,13 @@ All endpoints are under `/api`. Request and response bodies are JSON.
 
 #### `GET /api/instances`
 
-Returns all instances, sorted by name. All query parameters are optional.
+Returns all instances sorted by name. All query parameters are optional.
 
-| Parameter | Type   | Description                             |
-|-----------|--------|-----------------------------------------|
-| `search`  | string | Partial match on `name` or `vmid`       |
-| `state`   | string | Exact match: `deployed`, `testing`, `degraded` |
-| `stack`   | string | Exact match: `production`, `development` |
+| Parameter | Type | Description |
+|---|---|---|
+| `search` | string | Partial match on `name`, `vmid`, or `stack` |
+| `state` | string | Exact match: `deployed`, `testing`, `degraded` |
+| `stack` | string | Exact match: `production`, `development` |
 
 ```
 GET /api/instances?search=plex&state=deployed
@@ -64,11 +63,11 @@ GET /api/instances?search=plex&state=deployed
     "state": "deployed",
     "stack": "production",
     "tailscale_ip": "100.64.0.1",
-    "atlas": 1, "argus": 0, "semaphore": 0,
+    "atlas": 1, "argus": 1, "semaphore": 0,
     "patchmon": 1, "tailscale": 1, "andromeda": 0,
     "hardware_acceleration": 1,
-    "created_at": "2024-01-15T10:30:00.000Z",
-    "updated_at": "2024-03-10T14:22:00.000Z"
+    "created_at": "2024-01-15T10:30:00",
+    "updated_at": "2024-03-10T14:22:00"
   }
 ]
 ```
@@ -91,10 +90,43 @@ GET /api/instances/stacks
 Returns a single instance by VMID.
 
 | Status | Condition |
-|--------|-----------|
-| `200`  | Instance found |
-| `404`  | No instance with that VMID |
-| `400`  | VMID is not a valid integer |
+|---|---|
+| `200` | Instance found |
+| `400` | VMID is not a valid integer |
+| `404` | No instance with that VMID |
+
+---
+
+#### `GET /api/instances/:vmid/history`
+
+Returns the audit log for an instance — newest events first.
+
+| Status | Condition |
+|---|---|
+| `200` | History returned (may be empty array) |
+| `400` | VMID is not a valid integer |
+| `404` | No instance with that VMID |
+
+```json
+[
+  {
+    "id": 3,
+    "vmid": 117,
+    "field": "state",
+    "old_value": "testing",
+    "new_value": "deployed",
+    "changed_at": "2024-03-10T14:22:00"
+  },
+  {
+    "id": 1,
+    "vmid": 117,
+    "field": "created",
+    "old_value": null,
+    "new_value": null,
+    "changed_at": "2024-01-15T10:30:00"
+  }
+]
+```
 
 ---
 
@@ -103,21 +135,21 @@ Returns a single instance by VMID.
 Creates a new instance. Returns the created record.
 
 | Status | Condition |
-|--------|-----------|
-| `201`  | Created successfully |
-| `400`  | Validation error (see `errors` array in response) |
-| `409`  | VMID already exists |
+|---|---|
+| `201` | Created successfully |
+| `400` | Validation error — see `errors` array in response |
+| `409` | VMID already exists |
 
 **Request body:**
 
 | Field | Type | Required | Notes |
-|-------|------|----------|-------|
+|---|---|---|---|
 | `name` | string | yes | |
-| `vmid` | integer | yes | Must be > 0, unique |
+| `vmid` | integer | yes | Must be > 0 and unique |
 | `state` | string | yes | `deployed`, `testing`, or `degraded` |
 | `stack` | string | yes | `production` or `development` |
-| `tailscale_ip` | string | no | Defaults to `""` |
-| `atlas` | 0\|1 | no | Defaults to `0` |
+| `tailscale_ip` | string | no | Valid IPv4 or empty string |
+| `atlas` | 0\|1 | no | |
 | `argus` | 0\|1 | no | |
 | `semaphore` | 0\|1 | no | |
 | `patchmon` | 0\|1 | no | |
@@ -132,11 +164,11 @@ Creates a new instance. Returns the created record.
 Replaces all fields on an existing instance. Accepts the same body shape as `POST`. The `vmid` in the body may differ from the URL — this is how you change a VMID.
 
 | Status | Condition |
-|--------|-----------|
-| `200`  | Updated successfully |
-| `400`  | Validation error |
-| `404`  | No instance with that VMID |
-| `409`  | New VMID conflicts with an existing instance |
+|---|---|
+| `200` | Updated successfully |
+| `400` | Validation error |
+| `404` | No instance with that VMID |
+| `409` | New VMID conflicts with an existing instance |
 
 ---
 
@@ -145,11 +177,36 @@ Replaces all fields on an existing instance. Accepts the same body shape as `POS
 Deletes an instance. Only instances on the `development` stack may be deleted.
 
 | Status | Condition |
-|--------|-----------|
-| `204`  | Deleted successfully |
-| `404`  | No instance with that VMID |
-| `422`  | Instance is on the `production` stack |
-| `400`  | VMID is not a valid integer |
+|---|---|
+| `204` | Deleted successfully |
+| `400` | VMID is not a valid integer |
+| `404` | No instance with that VMID |
+| `422` | Instance is on the `production` stack |
+
+---
+
+### Backup
+
+#### `GET /api/export`
+
+Downloads a JSON backup of all instances as a file attachment.
+
+```json
+{
+  "version": 1,
+  "exported_at": "2024-03-10T14:22:00.000Z",
+  "instances": [ ... ]
+}
+```
+
+#### `POST /api/import`
+
+Replaces all instances from a JSON backup. Validates every row before committing — if any row is invalid the entire import is rejected.
+
+| Status | Condition |
+|---|---|
+| `200` | Import successful — returns `{ "imported": N }` |
+| `400` | Body missing `instances` array, or validation errors |
 
 ---
 
@@ -157,42 +214,30 @@ Deletes an instance. Only instances on the `development` stack may be deleted.
 
 ```bash
 npm install
-npm test          # run all tests once
+npm test            # run all tests once
 npm run test:watch  # watch mode
-npm start         # start the server on :3000
+npm start           # start the server on :3000
 ```
 
 Tests are split across three files:
 
 | File | What it covers |
-|------|----------------|
-| `tests/db.test.js` | SQLite data layer — all CRUD operations, constraints, filters |
+|---|---|
+| `tests/db.test.js` | SQLite data layer — CRUD, constraints, filters, history logging |
 | `tests/api.test.js` | HTTP API — all endpoints, status codes, error cases |
-| `tests/helpers.test.js` | UI helper functions — `esc()` XSS contract, `fmtDate()` |
+| `tests/helpers.test.js` | UI helpers — `esc()` XSS contract, date formatting, history formatters |
 
 ---
 
 ## Versioning
 
-Catalyst uses [semantic versioning](https://semver.org). `package.json` is the single source of truth for the version number.
+Catalyst uses [semantic versioning](https://semver.org). `package.json` is the single source of truth.
 
-| Change | Bump | Example |
-|--------|------|---------|
-| Bug fix | patch | `1.0.0` → `1.0.1` |
-| New feature, backward compatible | minor | `1.0.0` → `1.1.0` |
-| Breaking change | major | `1.0.0` → `2.0.0` |
+| Change | Bump |
+|---|---|
+| Bug fix | patch |
+| New feature, backward compatible | minor |
+| Breaking change | major |
 
-### Cutting a release
-
-```bash
-# 1. Bump version in package.json, then:
-git add package.json
-git commit -m "chore: release v1.1.0"
-git tag v1.1.0
-git push && git push --tags
-```
-
-Pushing a tag triggers the full CI pipeline: **test → build → release**.
-
-- Docker image tagged `:1.1.0`, `:1.1`, and `:latest` in the Gitea registry
-- A Gitea release is created at `v1.1.0`
+Pushing a tag triggers the CI pipeline: **test → build → release**.
+Docker images are tagged `:x.y.z`, `:x.y`, and `:latest`.
diff --git a/server/routes.js b/server/routes.js
index a2132d4..c48ef93 100644
--- a/server/routes.js
+++ b/server/routes.js
@@ -28,9 +28,16 @@ function validate(body) {
   return errors;
 }
 
+function handleDbError(context, e, res) {
+  if (e.message.includes('UNIQUE')) return res.status(409).json({ error: 'vmid already exists' });
+  if (e.message.includes('CHECK'))  return res.status(400).json({ error: 'invalid field value' });
+  console.error(context, e);
+  res.status(500).json({ error: 'internal server error' });
+}
+
 function normalise(body) {
   const row = {
-    name:                  body.name.trim(),
+    name:                  (body.name ?? '').trim(),
     state:                 body.state,
     stack:                 body.stack,
     vmid:                  body.vmid,
@@ -84,10 +91,7 @@ router.post('/instances', (req, res) => {
     const created = getInstance(data.vmid);
     res.status(201).json(created);
   } catch (e) {
-    if (e.message.includes('UNIQUE')) return res.status(409).json({ error: 'vmid already exists' });
-    if (e.message.includes('CHECK'))  return res.status(400).json({ error: 'invalid field value' });
-    console.error('POST /api/instances', e);
-    res.status(500).json({ error: 'internal server error' });
+    handleDbError('POST /api/instances', e, res);
   }
 });
 
@@ -105,10 +109,7 @@ router.put('/instances/:vmid', (req, res) => {
     updateInstance(vmid, data);
     res.json(getInstance(data.vmid));
   } catch (e) {
-    if (e.message.includes('UNIQUE')) return res.status(409).json({ error: 'vmid already exists' });
-    if (e.message.includes('CHECK'))  return res.status(400).json({ error: 'invalid field value' });
-    console.error('PUT /api/instances/:vmid', e);
-    res.status(500).json({ error: 'internal server error' });
+    handleDbError('PUT /api/instances/:vmid', e, res);
   }
 });
 
@@ -155,7 +156,6 @@ router.delete('/instances/:vmid', (req, res) => {
     deleteInstance(vmid);
     res.status(204).end();
   } catch (e) {
-    console.error('DELETE /api/instances/:vmid', e);
-    res.status(500).json({ error: 'internal server error' });
+    handleDbError('DELETE /api/instances/:vmid', e, res);
   }
 });
diff --git a/tests/api.test.js b/tests/api.test.js
index 1209ec9..66852ce 100644
--- a/tests/api.test.js
+++ b/tests/api.test.js
@@ -303,6 +303,12 @@ describe('POST /api/import', () => {
   it('returns 400 if body has no instances key', async () => {
     expect((await request(app).post('/api/import').send({})).status).toBe(400)
   })
+
+  it('returns 400 (not 500) when a row is missing name', async () => {
+    const res = await request(app).post('/api/import')
+      .send({ instances: [{ ...base, name: undefined, vmid: 1 }] })
+    expect(res.status).toBe(400)
+  })
 })
 
 // ── Static assets & SPA routing ───────────────────────────────────────────────
diff --git a/tests/helpers.test.js b/tests/helpers.test.js
index d6c1a4a..587aa14 100644
--- a/tests/helpers.test.js
+++ b/tests/helpers.test.js
@@ -145,6 +145,64 @@ describe('version label formatting', () => {
   })
 })
 
+// ── fmtHistVal() ─────────────────────────────────────────────────────────────
+// Mirrors the logic in ui.js — formats history field values for display.
+
+const BOOL_FIELDS = ['atlas','argus','semaphore','patchmon','tailscale','andromeda','hardware_acceleration']
+
+function fmtHistVal(field, val) {
+  if (val == null || val === '') return '—'
+  if (BOOL_FIELDS.includes(field)) return val === '1' ? 'on' : 'off'
+  return val
+}
+
+describe('fmtHistVal', () => {
+  it('returns — for null', () => {
+    expect(fmtHistVal('state', null)).toBe('—')
+  })
+
+  it('returns — for empty string', () => {
+    expect(fmtHistVal('state', '')).toBe('—')
+  })
+
+  it('returns on/off for boolean service fields', () => {
+    expect(fmtHistVal('atlas', '1')).toBe('on')
+    expect(fmtHistVal('atlas', '0')).toBe('off')
+    expect(fmtHistVal('hardware_acceleration', '1')).toBe('on')
+  })
+
+  it('returns the value as-is for non-boolean fields', () => {
+    expect(fmtHistVal('state', 'deployed')).toBe('deployed')
+    expect(fmtHistVal('name', 'plex')).toBe('plex')
+    expect(fmtHistVal('tailscale_ip', '100.64.0.1')).toBe('100.64.0.1')
+  })
+})
+
+// ── stateClass() ─────────────────────────────────────────────────────────────
+// Mirrors the logic in ui.js — maps state values to timeline CSS classes.
+
+function stateClass(field, val) {
+  if (field !== 'state') return ''
+  return { deployed: 'tl-deployed', testing: 'tl-testing', degraded: 'tl-degraded' }[val] ?? ''
+}
+
+describe('stateClass', () => {
+  it('returns empty string for non-state fields', () => {
+    expect(stateClass('name', 'plex')).toBe('')
+    expect(stateClass('stack', 'production')).toBe('')
+  })
+
+  it('returns the correct colour class for each state value', () => {
+    expect(stateClass('state', 'deployed')).toBe('tl-deployed')
+    expect(stateClass('state', 'testing')).toBe('tl-testing')
+    expect(stateClass('state', 'degraded')).toBe('tl-degraded')
+  })
+
+  it('returns empty string for unknown state values', () => {
+    expect(stateClass('state', 'unknown')).toBe('')
+  })
+})
+
 // ── CSS regressions ───────────────────────────────────────────────────────────
 
 const css = readFileSync(join(__dirname, '../css/app.css'), 'utf8')