JSPM

punctilio (n.): precise observance of formalities.

Pretty good at making your text pretty. The most feature-complete and reliable English typography package.

import { transform } from 'punctilio'

transform('"It\'s a beautiful thing, the destruction of words..." -- 1984')
// → “It’s a beautiful thing, the destruction of words…”—1984

npm install punctilio

Why punctilio?

As far as I can tell, punctilio is the most reliable and feature-complete. I built punctilio for my website. I wrote[^wrote] and sharpened the core regexes sporadically over several months, exhaustively testing edge cases. Eventually, I decided to spin off the functionality into its own package.

[^wrote]: While Claude is the number one contributor to this repository, that’s just because Claude has helped me port my existing code and add minor features. The core regular expressions (e.g. dashes, quotes, multiplication signs) are human-written. Those numerous commits don’t show in this repo’s history.

I tested punctilio 1.2.9 against smartypants 0.2.2, tipograph 0.7.4, smartquotes 2.3.2, typograf 7.6.0, and retext-smartypants 6.2.0.[^python] These other packages have spotty feature coverage and inconsistent impact on text. For example, smartypants mishandles quotes after em dashes (though quite hard to see in GitHub’s font) and lacks multiplication sign support.

[^python]: The Python libraries I found were closely related to the JavaScript packages. I tested them and found similar scores, so I don’t include separate Python results.

My benchmark.mjs measures how well libraries handle a wide range of scenarios. The benchmark normalizes stylistic differences (e.g. non-breaking vs regular space, British vs American dash spacing) for fair comparison.

Known limitations of punctilio

Test suite

Setting aside the benchmark, punctilio’s test suite includes 600+ tests at 100% branch coverage, including edge cases derived from competitor libraries (smartquotes, retext-smartypants, typograf), and the Standard Ebooks typography manual. Key test categories:

• Quote handling: Unicode text, nested quotes, contractions, Irish names (O’Brien), leading apostrophes (’99, ’twas)
• Dash transformations: Year/page/score ranges, model name preservation (Llama-2-7B, GPT-4), phone numbers, ISBNs
• Symbol transforms: Measurements (6′2″), coordinates (40° 44′ N), temperatures, fractions, math symbols
• Idempotency: All transformations are verified to be stable when applied multiple times
• Separator boundaries: Tests verify HTML DOM integration doesn’t break patterns

Works with HTML DOMs via separation boundaries

Other typography libraries either transform plain strings or operate on AST nodes individually (retext-smartypants can’t map changes back to HTML). But real HTML has text spanning multiple elements—if you concatenate text from <em>Wait</em>..., transform it, then try to split it back, youve lost track of where </em> belonged.

punctilio introduces separation boundaries. First, insert a “separator” character (default: U+E000) at each element boundary before transforming (like at the start and end of an <em>). Every regex allows this character mid-pattern without breaking matches. For example, “.[SEP]..” still becomes “…[SEP]”. punctilio validates the output by ensuring the separator count remains the same.

import { transform, DEFAULT_SEPARATOR } from 'punctilio'

transform(`"Wait${DEFAULT_SEPARATOR}"`)
// → `“Wait”${DEFAULT_SEPARATOR}`
// The separator doesn’t block the information that this should be an end-quote!

For rehype / unified pipelines, use the built-in plugin which handles the separator logic automatically:

import rehypePunctilio from 'punctilio/rehype'

unified()
  .use(rehypeParse)
  .use(rehypePunctilio, { dashStyle: 'american' })
  .use(rehypeStringify)
  .process('<p>"Hello..." -- world</p>')
// → <p>"Hello…"—world</p>

For manual DOM walking or custom transforms, use transformElement from punctilio/rehype. Note: punctilio transforms plain text or HTML—not raw Markdown.

Options

punctilio doesn't enable all transformations by default. Fractions and degrees tend to match too aggressively (perfectly applying the degree transformation requires semantic meaning). Superscript letters and punctuation ligatures have spotty font support. Furthermore, ligatures = true can change the meaning of text by collapsing question and exclamation marks. Non-breaking spaces are also opt-in since they alter whitespace throughout the text.

transform(text, {
  punctuationStyle: 'american' | 'british' | 'none',  // default: 'american'
  dashStyle: 'american' | 'british' | 'none',         // default: 'american'

  symbols: true,           // math, legal, arrows, primes
  collapseSpaces: true,    // normalize whitespace
  fractions: false,        // 1/2 → ½
  degrees: false,          // 20 C → 20 °C
  superscript: false,      // 1st → 1ˢᵗ
  ligatures: false,        // ??? → ⁇, ?! → ⁈, !? → ⁉, !!! → !
  nbsp: false,             // non-breaking spaces (after honorifics, between numbers and units, etc.)
  checkIdempotency: true,  // verify transform(transform(x)) === transform(x)
})

• Prime marks (5'10" → 5′10″) require semantic understanding to distinguish from closing quotes (e.g. "Term 1" should produce closing quotes). punctilio counts quotes to heuristically guess whether the matched number at the end of a quote (if not, it requires a prime mark). Other libraries like tipograph 0.7.4 use simpler patterns that make more mistakes. That said, punctilio is still not perfect and will sometimes wrongly convert to ending quotation marks: transform('I said "5" sounds right"') will wrongly produce a closed double quote after the 5” instead of a double prime (correct).
• The american style follows the Chicago Manual of Style:
  • Periods and commas go inside quotation marks (“Hello,” she said.)
  • Unspaced em-dashes between words (word—word)
• The british style follows Oxford style:
  • Periods and commas go outside quotation marks (“Hello”, she said.)
  • Spaced en-dashes between words (word – word)
• punctilio is idempotent by design: transform(transform(text)) always equals transform(text). If performance is critical, set checkIdempotency: false to skip the verification pass.