---
name: Contextual alternates
slug: contextual-alternates
category: typography
status: published
created: 2026-08-21T00:00:00.000Z
modified: 2026-08-21T00:00:00.000Z
definition: Substitute letterforms a font swaps in automatically based on the
  neighbouring characters, so joins and repeats look natural.
aliases:
  - name: calt
    source: opentype
  - name: contextual forms
  - name: contextual substitution
tags:
  - fonts
relations:
  contrastWith:
    - ligature
    - opentype-features
    - stylistic-set
    - swash
  variantOf: []
  partOf: []
  seeAlso: []
implementations: []
sources:
  - title: Syntax for OpenType features in CSS (Adobe Fonts)
    url: https://helpx.adobe.com/fonts/using/open-type-syntax.html
  - title: Registered features, a-e (OpenType spec)
    url: https://learn.microsoft.com/en-us/typography/opentype/spec/features_ae
demo: inline
exhibit: false
useWhen: a script font changes shape depending on its neighbours
---

Some letters look wrong next to certain others. A joining script whose exit stroke
lands on the entry stroke of the next letter needs a different exit when the next
letter is a tall one. A doubled letter drawn from one outline twice reads as a
stamp rather than as handwriting. The `calt` feature is a font's own answer to
those cases: a table of rules saying which glyph to use when a particular
neighbour is present, applied by the shaping engine with no decision from the
person setting the text.

That automatic quality is the whole distinction from its neighbours in the
[OpenType](/opentype-features) vocabulary. A [stylistic set](/stylistic-set) is a
deliberate editorial switch: you prefer the other `a`, and you say so. Contextual
alternates fire on their own, wherever the context calls for them, and they are on
by default in CSS, which is why most people never learn the tag exists.
A [ligature](/ligature) is close but not the same shape of rule: it fuses a pair
into one glyph, while a contextual alternate keeps the count of glyphs and changes
which drawing one of them uses. In practice the two overlap, and programming faces
lean on `calt` heavily, both for arrows built out of `-` and `>` and for keeping
repeated symbols from stacking into one blur.

The CSS is two spellings of the same request. `font-variant-ligatures: contextual`
and `no-contextual` are the readable form, and `font-feature-settings: "calt" 1`
or `0` is the raw tag. Turning it off is the rarer and more interesting case:
a code editor showing exactly the characters in the file, a diagram where `->`
must stay two characters wide, a table where a substitution would break the
column. Otherwise leave it alone, because the type designer wrote those rules
about their own drawings and knows where the collisions are.

The trap is the same one every OpenType tag carries: a request for a feature the
file does not have is silently ignored, and most text faces have no `calt` table
at all. Nothing warns you, so a script that looks mechanical is not evidence that
the browser dropped the feature; it is usually evidence that the font never
shipped one. The specimen above is set in Fira Code, which does ship one, so its
switch asks the real question and the glyphs answer it. Ask the same question of
a text face with no `calt` table and both states come back identical, which is
what the silence looks like from the outside.