  ┌─────────────────────┐
  │                     │
  │   C  O  D  A        │
  │                     │
  │   22 keys.          │
  │   The distilled     │
  │   form.             │
  └─────────────────────┘

CODA

22 keys. The distilled form of Cadenza.

v0.1 · Concept Colemak-DH 9 layers 39 Tap Dances QMK keymap.c SFB ~0.90% No pinky · No inner column

Coda (n.): the concluding passage — a concentrated, essential statement that brings everything together.

Coda is a 22-key split keyboard layout and the minimal sibling of Cadenza. Designed for German + English prose, shell/code work, and tiling window manager use — without pinkies, without an inner column, and with an estimated SFB rate lower than Colemak-DH.

Physical Layout
Design Principles
Letter Placement
Ergonomic Metrics
Comparison
Layer Architecture
Layer Reference
Tap Dance Reference (39)
Macro Reference (16)
Combo Reference (9)
Hardware & Firmware
Known Limitations
Roadmap

Physical Layout

  Left                    Right
 ┌───┬───┬───┐            ┌───┬───┬───┐
 │ L │ G │ D │            │ H │ F │ C │   ← top row
 ├───┼───┼───┤            ├───┼───┼───┤
 │ R │ S │ T │            │ N │ E │ I │   ← home row
 ├───┼───┼───┤            ├───┼───┼───┤
 │ B │ W │ M │            │ Z │ K │ U │   ← bottom row
 └───┴───┴───┘            └───┴───┴───┘
         ┌───┬───┐    ┌───┬───┐
         │ A │Spc│    │ O │Ent│           ← thumbs
         └───┴───┘    └───┴───┘

 Fingers per half (outer→inner): Ring · Middle · Index   (no Pinky, no Inner column)
 A, Spc, O, Ent = letters (tap) + layer access (hold)

Design Principles

No pinky column — by design, not constraint. The pinky is the weakest finger and primary RSI source. Removing it forces better decisions everywhere else.
No inner column. Lateral index finger movement destabilises hand position. Enforced physically on Coda.
Strongest finger earns highest priority. Index > Middle > Ring within every row and every layer.
A and O on thumbs. These two (7.4% and 5.0%) were on pinkies in Colemak-DH. Thumbs give the highest-frequency non-home letters to the strongest fingers.
Colemak-DH inner home row preserved. T·S·R / N·E·I — identical to Cadenza. Zero muscle-memory penalty.
Frequency × Ergonomic quality = access key rank. A thumb earns Navigation (most-used non-alpha function) because it is the best thumb position.
Bilateral access for layer triggers and Meta. Code (G/F), WM (M/U), Fn (D/C), and Meta (L/H) are each reachable from either hand. Holding the right-hand key frees the left for numpad-style input.
NEIO = ← ↓ ↑ → everywhere. Arrows, WM focus switching, window movement — same spatial convention throughout.
Combos replace dedicated keys. Space+Enter=Backspace. N+E=↑. Z+K=PgUp. Physical positions freed for valuable use.
QMK keymap.c — not Vial. Layer-specific combos, unlimited macros, full C programmability.

Letter Placement

Letters placed by combined German + English frequency, assigned to fingers in strength order, avoiding same-column bigrams.

Rank	Letter	Freq	Position	Rationale
1	E	15.0%	R home middle	Highest frequency → best position. ER cross-hand ✓
2	N	8.0%	R home index	Strongest right finger. EN inward roll ✓
3	T	7.5%	L home index	Strongest left finger. TH cross-hand ✓
4	A	7.4%	L thumb	Thumb solves pinky-removal gap. AN cross ✓
5	I	7.3%	R home ring	Colemak home ✓. IN inward roll ✓. IE inward roll ✓
6	S	6.8%	L home middle	ST inward roll ✓. Colemak home ✓
7	R	6.5%	L home ring	ER cross-hand ✓. Colemak home ✓
8	H	5.5%	R top index	TH cross-hand ✓. CH = C→H right inward roll ✓✓
9	O	5.0%	R thumb	Thumb solves pinky-removal gap
10	D	4.7%	L top index	DE cross-hand ✓ (German der/die/das)
11	L	3.7%	L top ring	EL cross-hand ✓. Hold=Meta
12	U	3.6%	R bot ring	Avoids EU same-finger (E=R-mid) and UN same-finger (N=R-idx)
13	C	2.8%	R top ring	CH inward roll ✓✓ (German most common digraph 2.4%)
14	G	2.5%	L top middle	IG cross-hand ✓ (German -ig: richtig, wenig, möglich)
15–20	M W F B Z K	1.0–2.5%	Bottom rows	Less frequent — acceptable positions. Z on base for German "zu"
Overflow: P(0.8%) · V(0.7%) · Y(0.4%) · J(0.2%) · X(0.1%) · Q(0.05%) — combined ~3% — via Hold A+Ent

Ergonomic Metrics

Metric	Value	Notes
SFB rate	~0.90%	Estimated from column-pair bigram analysis
Home row usage (fingers)	51.1%	T+S+R+N+E+I frequencies
Home row usage (+ thumbs A/O)	63.5%	Effective home-accessible character percentage
Pinky load	0%	No pinky column — physically zero
Lateral index stretch	Zero	No inner column — physically impossible
Hand balance	~46% L / 54% R	Right-heavy due to E (15%) on right middle
Heaviest single finger	R-Middle 17.9%	E(15%)+F(1.9%)+K(1.0%) — all on home row (best position)

Comparison

Metric	QWERTZ	Dvorak	Colemak-DH	Coda
SFB rate	6.31%	2.62%	1.28%	~0.90%
Home row usage	34%	71%	68%	64%
Pinky load	~14%	~7%	~6%	0%
Lateral stretch	Very high	Moderate	Low	Zero
German CH bigram	Same-finger	Cross-hand	Cross-hand	Inward roll
German IG bigram	Same-hand	Varies	Varies	Cross-hand
German EI bigram	Same-hand	Same-hand	Same-hand	Adjacent outward roll
Hardware availability	Any	Any	Any/remap	Custom 22-key PCB
Learning curve	None	Very high	High	Extreme

QWERTZ, Dvorak, Colemak-DH SFB values: documented (carpalx / Patrick Steele corpus). Coda: estimated from column-pair analysis.

vs. Cadenza

Dimension	Cadenza v1.0.0	Coda v0.1
Keys	36	22
Pinky load	~5%	0%
Base-layer letters	26	20 (+6 overflow)
Layers	13	9
Tap dances	43	34
Combos	0	9 (incl. layer-specific)
Firmware	Vial / QMK	QMK keymap.c only
Hardware	Corne Choc — available	Custom PCB — concept
Status	Daily driver · v1.0.0 stable	Concept · v0.1

Layer Architecture

Layer	Name	Access	Purpose
L0	Base	Always active	20 letters + HRM
L1-Over	Overflow / International	Hold `Spc`	P V Y J X Q · ä ö ü · ß €
L2-Sym	Symbols	Hold `Ent`	Symbols · Punctuation · Brackets
L3-Num	Numbers	Hold `O`	Numpad 1–9 · Operators
L4-Nav	Navigation	Hold `A`	Arrows · Word nav · Modifiers
L5-Mouse	Mouse	Tap-then-Hold `A`	Pointer · Scroll · Buttons
L6-Fn	Function + Media	Hold `D` or `C`	F1–F12 · Media
L7-Code	Code / CLI	Hold `G` or `F`	Shell operators · Path nav · Code macros
L8-WM	Tiling WM	Hold `M` or `U`	Workspaces 1–10 · Focus · Window movement

Layer Reference

Alpha

HRM · Modifier

Layer access

Navigation

Symbol

Number

Media

Macro · Shell

Tap Dance action

F-key

WM Workspace

WM Window

Combo key

International

Inactive

L0BaseAlways active — HRM via Tap Dance

Colemak-DH inner home row preserved unchanged (R·S·T / N·E·I). A and Ent on thumbs solve the pinky-removal gap. Layer access distributed bilaterally: D/C (top corners — left index, right ring) carry Fn, G/F (top middle column) carry Code, M/U (bottom corners — left index, right ring) carry WM. L (left ring top) and H (right index top) carry Meta as a tap/hold modifier — same HRM pattern as the home row.

LMeta

GCLI

DFn

RAlt

SCtrl

TShift

MWM

Atap · Nav

Spctap · Ovfl

HMeta

FCLI

CFn

NShift

ECtrl

IAltGr

UWM

Otap · Num

Enttap · Sym

L1-OverOverflow / InternationalHold Spc

P/V/Y on left home (strongest fingers, most frequent overflow letters). J/X/Q on left top. Umlauts placed at their base-letter positions for muscle-memory consistency: ä on A, ö on O, ü on U. ß on Z (AltGr+S) · € on K (AltGr+5).

äA

★ heldSpc

ßZ·AltGr

€K·AltGr

üU

öO

EntEnt

L2-SymSymbolsHold Ent

Frequency+Strength: = (rank 1) on T (strongest left finger). . , : on right home — most common prose punctuation. Bracket pairs as Tap Dance: tap=open, hold=close. ( ) on H · [ ] on F · < > on C · { } on U. *|@ on Spc (TD_STAR_AT). L falls through to base (Meta hold).

MetaL

-S

=T·rank1

_A·rank4

*|@Spc·TD

(|)H·TD

[|]F·TD

<|>C·TD

`K·TD

{|}U·TD

★ heldEnt

L3-NumNumbersHold O

Numpad layout on left hand — ring=1/4/7 · middle=2/5/8 · index=3/6/9. Same spatial positions as L8-WM workspace keys. 0 on A-thumb. € via AltGr+5 (direct keycode, same as Cadenza).

7L·rng

8G·mid

9D·idx

4R·rng

5S·mid

6T·idx

1B·rng

2W·mid

3M·idx

0A-thumb

.Spc·dec

.H·idx

/F·mid

=C·rng

(N·idx

,E·mid

*I·rng

-Z·idx

€K·AltGr

U·rng

★ heldO

EntEnt

L4-NavNavigationHold A

All 4 arrows on right side: ← ↓ → on home row (N·E·I), ↑ on F (above ↓ for inverted-T cluster). Home/PgDn/End on right bottom. PgUp via Z+K combo. Word-skip on C (Ctrl+←) and H. Del on Enter thumb. Modifiers on left for Shift+arrows (selection).

CapsL

MetaD

AltR

CtrlS

ShiftT

PasteB

CopyW

UndoM

★ heldA

CutSpc

Ctrl+←H·word

↑F

Ctrl+←C·word

←N·idx

↓E·mid

→I·rng

HomeZ·idx

PgDnK·mid

EndU·rng

Scrl↑O

DelEnt

L5-MouseMouseTap-then-Hold A

Tap A, then hold — different tap-dance state from plain Hold-A (Nav). Mouse movement on right (N=← E=↓ I=→ H=↑). Scroll on right middle column. Modifiers on left for Shift-click, Ctrl-click. Buttons on right thumbs.

MetaD

AltR

CtrlS

ShiftT

★ heldA

SpcSpc

M↑H

Scrl↑F

M←N

M↓E

M→I

Scrl↓K

Btn1O

Btn2Ent

L6-FnFunction + MediaHold D or C (bilateral)

F1–F9 on left in numpad positions (same spatial shape as L3-Num — muscle memory transfers). F10–F12 on right home. Media controls on right. Hold C (right) frees the left for the F-key numpad. ⚠ When holding D (left, index top), F9 is occupied by the trigger — use the right-hand C-hold for full F-key numpad access.

F7L

F8G

★ heldD

F4R

F5S

F6T

F1B

F2W

F3M

Vol-A

Vol+Spc

PrevH

PrtScF

★ heldC

F10N

F11E

F12I

MuteZ

PlayK

StopU

EntEnt

L7-CodeCode / CLIHold G or F (bilateral)

Bilateral middle-finger top access — hold the right G/F to free the left for code typing, or vice versa. Left home row: T= | · S=&& · R=||. Right home: N=TD(/ ~/hold ../dbl) · E=TD($()/${}) · I=TD(!= ==) · H=TD(=> ->). $? and 2>&1 on right bottom. Mirrors Cadenza L9.

★ heldG

||R·M16

&&S·M15

| T·M13

SpcSpc

=>|->H·TD

★ heldF

/|~/N·TD

$()|${}E·TD

!=|==I·TD

$?Z·M14

2>&1K·M12

EntEnt

L8-WMTiling WM — WS 1–10Hold M or U (bilateral)

Numpad positions: ring=WS1/4/7 · mid=WS2/5/8 · idx=WS3/6/9 · A-thumb=WS10. Tap=⊞+N (go) · Hold=⊞⇧+N (move window). Hold U (right) frees the left hand for the workspace numpad. ⚠ When holding M (left, index bot), WS3 is occupied by the trigger — use the right-hand U-hold for full numpad access.

WS7L·TD

WS8G·TD

WS9D·TD

WS4R·TD

WS5S·TD

WS6T·TD

WS1B·TD

WS2W·TD

★ heldM

WS10A·TD

SpcSpc

⊞+→H·focus

FullF·⊞F

FloatC·⊞Spc

⊞+←N·focus

⊞+↓E·focus

⊞+↑I·focus

⊞⇧+←Z·win

⊞⇧+↓K·win

★ heldU

KillEnt·⊞⇧Q

Tap Dance Reference

39 tap dances. QMK keymap.c — no slot limit. Tipping terms: index/middle = 200 ms · ring = 250 ms.

Thumb Layer Access (4)

TD	Key	Tap	Hold	Tap-then-Hold	ms
`TD_A`	A (L thumb · below B)	a	MO(Nav)	MO(Mouse)	200
`TD_SPC`	Space (L thumb · in gap)	Space	MO(Overflow)	—	200
`TD_O`	O (R thumb · in gap)	o	MO(Num)	—	200
`TD_ENT`	Enter (R thumb · below Z)	Enter	MO(Sym)	—	200

Bilateral Finger Layer Access (6)

TD	Key	Tap	Hold	ms
`TD_D`	D (L idx top)	d	MO(Fn)	200
`TD_C`	C (R rng top)	c	MO(Fn)	250
`TD_G`	G (L mid top)	g	MO(Code)	200
`TD_F`	F (R mid top)	f	MO(Code)	200
`TD_M`	M (L idx bot)	m	MO(WM)	200
`TD_U`	U (R rng bot)	u	MO(WM)	250

Meta Modifier (2)

TD	Key	Tap	Hold	ms
`TD_L`	L (L rng top)	l	KC_LGUI · Meta	250
`TD_H`	H (R idx top)	h	KC_LGUI · Meta	200

Home Row Mods / HRM (6)

TD	Key	Tap	Hold	ms
`TD_T`	T	t	Shift	200
`TD_S`	S	s	Ctrl	200
`TD_R`	R	r	Alt	250
`TD_N`	N	n	Shift	200
`TD_E`	E	e	Ctrl	200
`TD_I`	I	i	AltGr	250

Symbol Pairs — Sym Layer (7)

TD	Tap	Hold	Double	Usage
`TD_PAREN`	`(`	`)`	—	Sym layer H
`TD_SQBR`	`[`	`]`	—	Sym layer F
`TD_CURL`	`{`	`}`	—	Sym layer U
`TD_ANGLE`	`<`	`>`	—	Sym layer C
`TD_STAR_AT`	`*`	`@`	—	Sym layer Spc
`TD_QUOTE`	`"` dead key	`"` literal (M9)	—	German umlauts via dead key + vowel
`TD_BTICK`	` dead key	` literal (M10)	``` (M11)	Sym layer K

Code Actions — Code Layer (4)

TD	Tap	Hold	Double	Key / Layer
`TD_SLASH`	`/`	`~/` (M1)	`../` (M2)	Code N — path navigation
`TD_EXP`	`$()` + ← (M3)	`${}` + ← (M4)	—	Code E — shell expansion, cursor inside
`TD_CMP`	`!=` (M5)	`==` (M6)	—	Code I — comparison operators
`TD_ARR`	`=>` (M7)	`->` (M8)	—	Code H — arrow operators

Workspace Tap/Hold — WM Layer (10)

TD	Tap	Hold	Key position
`TD_WS1`	⊞+1 (go to WS1)	⊞⇧+1 (move window to WS1)	B · L-bot-ring
`TD_WS2`	⊞+2	⊞⇧+2	W · L-bot-mid
`TD_WS3`	⊞+3	⊞⇧+3	M · L-bot-idx
`TD_WS4`	⊞+4	⊞⇧+4	R · L-hom-ring
`TD_WS5`	⊞+5	⊞⇧+5	S · L-hom-mid
`TD_WS6`	⊞+6	⊞⇧+6	T · L-hom-idx
`TD_WS7`	⊞+7	⊞⇧+7	L · L-top-ring
`TD_WS8`	⊞+8	⊞⇧+8	G · L-top-mid
`TD_WS9`	⊞+9	⊞⇧+9	D · L-top-idx
`TD_WS10`	⊞+0	⊞⇧+0	A · L-thumb

Numpad positions: ring=WS1/4/7 · middle=WS2/5/8 · index=WS3/6/9 (same spatial memory as L3-Num)

Macro Reference

16 macros. In QMK keymap.c these are C functions with no slot limit.

ID	Output	Function	Triggered by
M1	`~/`	Home directory	TD_SLASH hold
M2	`../`	Parent directory	TD_SLASH double
M3	`$()` + ←	Shell expansion, cursor inside	TD_EXP tap
M4	`${}` + ←	Variable expansion, cursor inside	TD_EXP hold
M5	`!=`	Not equal	TD_CMP tap
M6	`==`	Equal	TD_CMP hold
M7	`=>`	Fat arrow (Python, JS, Rust)	TD_ARR tap
M8	`->`	Thin arrow / pointer	TD_ARR hold
M9	`"` + Space	Literal quote (US Intl dead-key bypass)	TD_QUOTE hold
M10	` + Space	Literal backtick (US Intl dead-key bypass)	TD_BTICK hold
M11	```	Markdown code fence	TD_BTICK double
M12	`2>&1`	Stderr redirect with spaces	Code K
M13	`\|`	Pipe with surrounding spaces	Code T
M14	`$?`	Last exit code	Code Z
M15	`&&`	And-chain	Code S
M16	`\|\|`	Or-chain	Code R

Combo Reference

9 combos — 7 global (any layer), 2 Nav-layer-specific.

Global combos

Keys	Type	Output	Notes
`Space + Enter`	tap	Backspace ★	Cross-hand, unambiguous, most critical
`A + O`	tap	Escape	Cross-hand
`A + Enter`	tap	Tab	Cross-hand diagonal
`Space + O`	tap	Delete	Cross-hand diagonal

Nav-layer combos COMBO_ONLY_FROM_LAYER

Keys	Output	Physical motion
`N + E`	↑ up arrow	Right index + middle simultaneously — adjacent, comfortable
`Z + K`	Page Up	Right index + middle, bottom row

Nav combos use COMBO_ONLY_FROM_LAYER in QMK — active only when Nav layer is on. This feature requires QMK keymap.c and is unavailable in Vial.

Hardware & Firmware

Hardware

Board	Keys	Gap from Coda target
Ferris Sweep / Bling	34	Has pinkies + inner column
Absolem	46	Too many keys
Custom PCB	22	Target — to be designed

Firmware

#define TAP_DANCE_ENTRIES    34
#define COMBO_COUNT          9
#define TAPPING_TERM         200    // overridden per-key for ring (250ms)
#define PERMISSIVE_HOLD             // helps HRM in fast typing
#define HOLD_ON_OTHER_KEY_PRESS     // for layer-access thumbs

// OS layout: US International
// ß = RALT(KC_S) · € = RALT(KC_5) · dead " for ä/ö/ü

Known Limitations

Limitation	Severity	Workaround
Custom hardware doesn't exist	Critical	Use Ferris Sweep (34 keys) as approximation
Backspace is a combo	High	Muscle memory adapts in 1–2 weeks
P, V on overflow layer	Medium	~1.5% of characters — acceptable
Extreme learning curve	Expected	New hardware + new paradigm

Roadmap

Version	Focus	Status
v0.1	Complete design — all layers, TDs, macros, combos, comparison	✓ Done
v0.2	Custom 22-key PCB design + QMK firmware	Planned
v0.3	30-day daily use · real SFB measurement · tipping term tuning	Planned
v1.0	Hardware open-sourced · firmware published · stable release	Planned

Coda v0.1 · Concept · April 2026 · one7two99 · MIT · github.com/one7two99/coda
Sibling of Cadenza · Based on Colemak-DH

CODA

Contents

Physical Layout

Design Principles

Letter Placement

Ergonomic Metrics

Comparison

vs. Cadenza

Layer Architecture

Layer Reference

Tap Dance Reference

Macro Reference

Combo Reference

Global combos

Nav-layer combos COMBO_ONLY_FROM_LAYER

Hardware & Firmware

Hardware

Firmware

Known Limitations

Roadmap