Custom formatter

priceFormat decides how prices become text on the main chart: Y-axis ticks, price tags beside horizontal grids, crosshair price, last price, OHLC panel, legend — all share one rule set.

Switch instruments often need different formats — BTC maybe 1 decimal, XRP 4, meme coins maybe compact 0.0{9}532. Modeled after TradingView’s price axis: use minMove + precision for most symbols; extreme display goes through type: "custom".

tip

With zero config the library picks a sensible precision from tick step. When instruments differ a lot (e.g. XRP at 4 decimals), pass priceFormat explicitly.

Three knobs

When configuring price format, these three controls matter (you can set only some):

Knob	What	Why
minMove	Minimum price increment (tick size)	Bounds tick step and decimal floor. e.g. 0.0001 → at least 4 decimals
precision	Display decimal places	Labels show at least this many; optional, derived from minMove + tick step
formatter	Custom format function	Only for type: "custom"; fully owns the string; minMove still aligns ticks

In short:

1. Display digits ≥ decimals implied by minMove (minMove=0.0001 → at least 4)
2. Tick step aligns with minMove (not smaller; preferably an integer multiple)
3. Once formatter is provided, label text follows it (escape hatch: currency prefix, localization, compact, etc.)

API

KeisenChart

Prop	Type	Description
priceFormat	PriceFormat	Main-chart price format; default { type: "price" }

PriceFormat

Union type — pick one:

type: "price" (built-in)

Field	Type	Default	Description
type	"price"	—	Use built-in algorithm
minMove	number?	—	tick size; omit to skip decimal / step floor
precision	number?	—	Display decimals; omit → derived from minMove + step
compactTiny	boolean?	false	Tiny values as 0.0{n}xxx
useGrouping	boolean?	true	Thousands separators (1,234.56)

type: "custom"

Field	Type	Description
type	"custom"	Fully custom labels
minMove	number?	Still affects tick step alignment
formatter	PriceFormatter	(value, ctx) => string

PriceFormatter / PriceFormatContext

type PriceFormatter = (value: number, ctx: PriceFormatContext) => string;

ctx field	Type	Description
kind	"tick" | "value"	tick: Y-axis; value: crosshair / OHLC / legend etc.
step	number?	Current nice tick step; mainly when kind === "tick"
domain	PriceDomain?	Current price domain for advanced custom formatters

Helpers

Function	Signature	Description
createPriceFormatter	(format?: PriceFormat) => PriceFormatter	Turn config into one function; reuse built-in logic inside custom
formatCompactTiny	(value, options?) => string | null	Tiny → 0.0{9}532; below threshold returns null
formatPrice	(value, ctx, opts?) => string	Built-in type: "price" entry

formatCompactTiny options:

Field	Type	Default	Description
significantDigits	number?	4	Significant digits
minLeadingZeros	number?	4	Min leading zeros to trigger compact

Example

Toggle normal precision vs custom ($ prefix / compact fallback):

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