diff --git a/docs/solo/README.md b/docs/solo/README.md
index fe4b9119..0973e098 100644
--- a/docs/solo/README.md
+++ b/docs/solo/README.md
@@ -59,7 +59,7 @@ history on the SD card and updates over WiFi.
 - [Screen lock](./lock.md): locking, auto-lock, PIN
 - [Hardware](./hardware.md): external keyboards and joysticks, e-ink, SD card, WiFi
 
-For developers: [UI Core](./developer/ui-core.md), [UI framework](./developer/ui-framework.md), [build flags](./developer/build-flags.md).
+For developers: [UI Core](./developer/ui-core.md), [UI framework](./developer/ui-framework.md), [build flags](./developer/build-flags.md), [feature matrix](./developer/feature-matrix.md).
 
 ## Contributors
 
diff --git a/docs/solo/developer/feature-matrix.md b/docs/solo/developer/feature-matrix.md
new file mode 100644
index 00000000..7c6dd0f3
--- /dev/null
+++ b/docs/solo/developer/feature-matrix.md
@@ -0,0 +1,121 @@
+## Feature matrix
+
+[Go back](../README.md)
+
+What each kind of screen gets. Solo has two UIs: **ui-new** (buttons, every
+board but the L2) and **ui-lvgl** (touch, the Wio Tracker L2). Within ui-new,
+some content depends on the screen's size and kind, the rest on the hardware
+(build flags).
+
+Keep this up to date: a change that adds a feature to only one UI, or only
+to some screens, adds or corrects its row here in the same commit.
+
+### Screen groups
+
+| Column | Boards | Logical size, font | Notes |
+| --- | --- | --- | --- |
+| **Small** | Wio Tracker L1 (OLED), Heltec V3/V4, GAT562 30S and Watch13, ProMicro, Cardputer ADV (TFT), T-Echo Lite (e-ink) | 128 × 64, 6 × 9 | The T-Echo Lite is e-ink, so it also gets what's marked *e-ink* |
+| **E-ink L** | Wio Tracker L1 e-ink, landscape | 250 × 122, 8 × 13 | Larger icons |
+| **E-ink P** | Wio Tracker L1 e-ink, portrait | 122 × 250, 6 × 9 | |
+| **E-ink 4.2"** | Wio Tracker L1 with the 4.2" panel (parked) | 400 × 300, 9 × 15 | Its own icon set |
+| **L2** | Wio Tracker L2 | 320 × 240 touch, ui-lvgl | |
+
+What decides it in ui-new (look for these when adding a screen):
+
+| Test | Where it's true |
+| --- | --- |
+| `Features::IS_EINK`, `display.isEink()` | E-ink L, E-ink P, E-ink 4.2", T-Echo Lite |
+| `expandHistory()`: 9 or more lines | E-ink L, E-ink P, E-ink 4.2" |
+| `height() >= 18 * lineHeight` | E-ink P, E-ink 4.2" |
+| `width() >= 40 * charWidth` ("wide") | E-ink 4.2" |
+| `isLandscape()` | Small, E-ink L, E-ink 4.2" |
+
+Cells: **yes**, **—** (not there), a short note where it differs, or the
+build flag it needs.
+
+### Messages
+
+| Feature | Small | E-ink L | E-ink P | E-ink 4.2" | L2 |
+| --- | --- | --- | --- | --- | --- |
+| Channels, direct, rooms | yes | yes | yes | yes | yes, one screen with sections |
+| Opens on the first unread, "New" line | yes | yes | yes | yes | yes |
+| Bubbles | 2-line boxes | whole text | whole text | whole text | whole text |
+| History kept | 48 ch / 32 DM | same | same | same | 256 / 128 in memory, all on SD (`HIST_ARCHIVE`) |
+| Path of a message | Path list | same | same | same | path diagram on the card |
+| Quick messages, placeholders | yes | yes | yes | yes | yes |
+| Bytes left while typing | yes | yes | yes | yes | yes |
+| Keyboard | letter grid or T9 | same | same, taller keys | same, taller keys | phone-style touch |
+| Cursor mode | yes | yes | yes | yes | — (touch places the cursor) |
+| Accents | Hold Enter on the letter | same | same | same | hold the key |
+| Message alert setting (banner / corner / off) | yes, no blink on e-ink | yes, no blink | yes, no blink | yes, no blink | banner on / off, tap to open |
+
+### Contacts and home
+
+| Feature | Small | E-ink L | E-ink P | E-ink 4.2" | L2 |
+| --- | --- | --- | --- | --- | --- |
+| Home | pages, Left / Right | same | same | same | swiped pages, apps six to a page |
+| Favourites | 6 slots, 3 columns | 3 columns | 2 columns | 3 columns | favourite chats page |
+| Quick panel | per-page quick rows | same | same | same | pull-down panel |
+| Nearby nodes | list | list, direction arrows | list, direction arrows | list + detail pane | Nodes app |
+| Map of nodes | yes (Nearby › Map) | yes | yes | yes | yes, on the tile map |
+| Contact details | yes | + compass rose, path hops | + compass rose, path hops | + compass rose, path hops | card with actions |
+| Contact expiry / prune | yes | yes | yes | yes | yes |
+| Remote admin | yes | yes | yes | yes | yes |
+
+### Navigation (`ENV_INCLUDE_GPS`)
+
+| Feature | Small | E-ink L | E-ink P | E-ink 4.2" | L2 |
+| --- | --- | --- | --- | --- | --- |
+| Trail | 512 points, simplified | same | same | same | 32 768 points, copy on SD |
+| Saved trail view | yes | yes | + map and elevation profile | + map and elevation profile | on the map, profile view |
+| GPX | over USB (USB tools) | same | same | same | to `trails/` on SD |
+| Waypoints, averaging | yes | yes | yes | yes | yes, 64 |
+| Target, navigation view | yes | yes | yes | wide layout | on the map + Compass app |
+| Live sharing, locator | yes | yes | yes | yes | yes |
+| Map | position, trail, target | same | same | same | offline tiles on SD, download over WiFi |
+
+### Tools and status
+
+| Feature | Small | E-ink L | E-ink P | E-ink 4.2" | L2 |
+| --- | --- | --- | --- | --- | --- |
+| Clock tools (alarm, timer, stopwatch) | yes, tenths on the stopwatch | no tenths | no tenths | wide layout | Clock app |
+| Calendar | Clock tools (tight grid) | Clock tools (tight grid) | + under the clock, on the lock screen | + under the clock | in the Clock app |
+| Remote bot, repeater, auto-advert | yes | yes | yes | yes | yes |
+| Melodies (`PIN_BUZZER`) | Ringtones tool | same | same | wide editor | Settings › Sound |
+| Status: Radio, GPS, Power, Mesh | yes, 32 min history | yes, 8 h charts | yes, 8 h charts | tiles with charts | Diagnostics app (+ noise chart) |
+| Sky view (`GPS_SKYVIEW`) | Status › Sky | same | same | + side panel | GPS app: Sky, Signal, Details |
+| Battery curve | Settings | same | same | same | Settings › Power, draggable chart |
+| QR code of the manual | Status › System, Enter | same | same | same | Settings › About |
+
+### Device
+
+| Feature | Small | E-ink L | E-ink P | E-ink 4.2" | L2 |
+| --- | --- | --- | --- | --- | --- |
+| Screen lock, PIN | yes | yes | yes | yes | yes, slide to unlock |
+| Magnetic cover (`PIN_HALL_SENSOR`) | yes | yes | yes | yes | — |
+| Brightness | yes (OLED, TFT) | — | — | — | yes |
+| Rotation, joystick rotation, full refresh | — | yes | yes | yes | — |
+| Power off | Shutdown page (hibernate) | same | same | same | Settings › System |
+| Firmware update | over USB | same | same | same | over WiFi from GitHub |
+| Screenshot (`ENABLE_SCREENSHOT`) | over USB | same | same | same | side + top button to SD, or over USB |
+| SD card, USB drive | — | — | — | — | yes |
+
+### Hardware add-ons (ui-new only)
+
+| Feature | Flag | Boards |
+| --- | --- | --- |
+| CardKB | `CARDKB_I2C` or `ENV_PIN_SDA` / `ENV_PIN_SCL` | any ui-new board with free I2C |
+| GPIO tool, `!gpio` | `PIN_GPIO1`..`PIN_GPIO4` | any ui-new board with free pins |
+| Wired joystick | `UI_HAS_JOYSTICK` | Heltec V3/V4 (and any board wired for it) |
+| Vibration | `PIN_VIBRATION` | GAT562 Watch13 |
+
+### Gaps
+
+Things one side has that the other could:
+
+- **L2 → ui-new**: history on an SD card (no card on the L1); a base map
+  under the trail and the nodes (no card either, but the L1 has 2 MB of QSPI
+  flash: a lite vector pack is being measured).
+- **ui-new → L2**: T9 layout; CardKB; GPIO on the Grove port; the magnetic
+  cover (no sensor).
+- **Small screens**: the e-ink charts (RAM: 8 h of history).