About these subsets

The subset fonts in this example use CSS unicode-range to load progressively, as needed. To quote MDN:

The unicode-range CSS descriptor sets the specific range of characters to be used from a font defined by @font-face and made available for use on the current page. If the page doesn't use any character in this range, the font is not downloaded; if it uses at least one, the whole font is downloaded.

See Appendix below for information on further font optimization strategies.

subset_range_english_basic

A B C D E F G H I J K L M N O P Q R S T U V W X Y Z a b c d e f g h i j k l m n o p q r s t u v w x y z 0 1 2 3 4 5 6 7 8 9 _ - ( ) [ ] { } # % \' " ‘ ’ “ ” * . , : ; ! ? / \ | @ & • + = < > ← ↑ → ↓ $ ^ ~ ©

subset_range_latin_1_punc

ª º ¹ ² ³ ¼ ½ ¾ « » ¡ ¿ ¦ § ¶ · ± ¬ ↔ ¢ £ ¤ ¥ ´ ¯ ¨ ¸ ® ° ↕ ↖ ↗ ↘ ↙ µ

subset_range_latin_ext

Ā Ă Ą Ć Ĉ Ċ Č Ď Ē Ĕ Ė Ę Ě Ĝ Ğ Ġ Ģ Ĥ Ĩ Ī Ĭ Į İ Ĵ Ķ Ĺ Ļ Ľ Ń Ņ Ň Ō Ŏ Ő Ŕ Ŗ Ř Ś Ŝ Ş Š Ţ Ť Ũ Ū Ŭ Ů Ű Ų Ŵ Ŷ Ÿ Ź Ż Ž Đ Ħ Ĳ Ŀ Ł Ŋ Œ Ŧ ā ă ą ć ĉ ċ č ď ē ĕ ė ę ě ĝ ğ ġ ģ ĥ ĩ ī ĭ į ĵ ķ ĺ ļ ľ ń ņ ň ō ŏ ő ŕ ŗ ř ś ŝ ş š ţ ť ũ ū ŭ ů ű ų ŵ ŷ ź ż ž đ ħ ı ĳ ĸ ŀ ł ŉ ŋ œ ŧ

subset_range_vietnamese

Ă Ạ Ả Ấ Ầ Ẩ Ẫ Ậ Ắ Ằ Ẳ Ẵ Ặ Ẹ Ẻ Ẽ Ế Ề Ể Ễ Ệ Ĩ Ỉ Ị Ơ Ọ Ỏ Ố Ồ Ổ Ỗ Ộ Ớ Ờ Ở Ỡ Ợ Ũ Ư Ụ Ủ Ứ Ừ Ử Ữ Ự Ỳ Ỵ Ỷ Ỹ Đ ă ạ ả ấ ầ ẩ ẫ ậ ắ ằ ẳ ẵ ặ ẹ ẻ ẽ ế ề ể ễ ệ ĩ ỉ ị ơ ọ ỏ ố ồ ổ ỗ ộ ớ ờ ở ỡ ợ ũ ư ụ ủ ứ ừ ử ữ ự ỳ ỵ ỷ ỹ đ ₫

subset_range_remaining

Ǻ Ȁ Ȃ Ḉ Ḍ Ḏ Ȅ Ȇ Ḕ Ḗ Ḝ Ǧ Ḡ Ḥ Ḫ Ȉ Ȋ Ḯ Ḷ Ḻ Ṃ Ṅ Ṇ Ṉ Ǫ Ȍ Ȏ Ȫ Ȭ Ȱ Ṍ Ṏ Ṑ Ṓ Ȑ Ȓ Ṛ Ṟ Ș Ṡ Ṣ Ṥ Ṧ Ṩ Ț Ṭ Ṯ Ȕ Ȗ Ṹ Ṻ Ẁ Ẃ Ẅ Ȳ Ẏ Ẓ Ǽ Ǿ Ə Ɲ Ǆ Ǉ Ǌ Ǳ ẞ Ω ǻ ȁ ȃ ḉ ḍ ḏ ȅ ȇ ḕ ḗ ḝ ǧ ḡ ḥ ḫ ȉ ȋ ḯ ḷ ḻ ṃ ṅ ṇ ṉ ǫ ȍ ȏ ȫ ȭ ȱ ṍ ṏ ṑ ṓ ȑ ȓ ṛ ṟ ș ṡ ṣ ṥ ṧ ṩ ț ṭ ṯ ẗ ȕ ȗ ṹ ṻ ẁ ẃ ẅ ȳ ẏ ẓ ǽ ǿ ǆ ǉ ǌ ǳ ȷ ə ɲ π ǅ ǈ ǋ ǲ ʹ ʺ ʻ ʼ ʾ ʿ ˈ ˉ ˊ ˋ ˌ ̀ ́ ̂ ̃ ̄ ̆ ̇ ̈ ̉ ̊ ̋ ̌ ̏ ̑ ̒ ̕ ̛ ̣ ̤ ̥ ̦ ̧ ̨ ̮ ̱ ̵ ⁰ ⁴ ⁵ ⁶ ⁷ ⁸ ⁹ ₀ ₁ ₂ ₃ ₄ ₅ ₆ ₇ ₈ ₉ ⅓ ⅔ ⅛ ⅜ ⅝ ⅞ ‐ ‒ – — ― ⟨ ⟩ ‰ ‚ „ ‹ › † ‡ … ⁄ ℓ № ′ ″ ‾ − ≤ ≥ ≈ ≠ ⁒ ∂ ∅ ∆ ∏ ∑ ∕ ∙ √ ∞ ∫ ≡ ▷ ◁ ฿ ₡ ₦ ₨ ₩ ₪ € ƒ ₭ ₱ ₲ ₴ ₵ ₸ ₹ ₺ ₼ ₽ ₿ ˝ ˆ ˇ ˘ ˜ ˙ ˚ ˛ ™ ℮ ■ □ ▲ △ ▶ ▼ ▽ ◀ ◆ ◇ ◊ ☐ ☑ ♡ ♥ ✓

Appendix

There are ways to further optimize Recursive:

If you only need part of the stylistic range (e.g. Monospace 0, Casual 1, Weight 300-800), variable fonts can be “instanced” or “partially instanced” with the FontTools Instancer. You can do it locally on the command line or in a Python script. Alternatively, the Google Fonts API allows you to do this by requesting a special URL, and the “Get Recursive” section of the Recursive Minisite has a UI to help construct these URLs.
You can tailor subsets and CSS unicode-range to your specific use case. E.g. if you are specifically writing in only English & Spanish, you could make a subset for this, using the FontTools Subsetter or by adapting my Recursive subsetting script if you want.
You can combine instancing and subsetting. For instance, if you want a particular font style for just a website’s logo, you could make a font file that just includes characters in the single style (or style range) you need for that, and load it separately. For example, the website https://sia.codes/ does something like this for the name Sia on the homepage.