punctilio (n.): precise observance of formalities.
Pretty good at making your text pretty. The most feature-complete and reliable English micro-typography package—transforms plain ASCII into typographically correct Unicode, even across HTML element boundaries.
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[1] 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.
I tested punctilio 1.7.13 against smartypants 0.2.2, tipograph 0.7.4, smartquotes 2.3.2, typograf 7.6.0, and retext-smartypants 6.2.0.[2] These other packages have spotty feature coverage and inconsistent impact on text. For example, smartypants mishandles quotes after em dashes and lacks multiplication sign support.
Input
smartypants
punctilio
5x5
5x5 (✗)
5×5 (✓)
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.
Leading apostrophe is indistinguishable from an opening quote without semantic understanding
«Bonjour»
Not spaced to « Bonjour »
French localization not supported
Test suite
Setting aside the benchmark, punctilio’s test suite includes 1,100+ tests at 100% branch coverage, including edge cases derived from competitor libraries (smartquotes, retext-smartypants, typograf), and the Standard Ebooks typography manual. Further, all transformations are stable when applied multiple times.
Works with HTML DOMs via separation boundaries
Perhaps the most innovative feature of the library is that it properly handles DOMs! (This means it'll also work on Markdown: convert to HTML, transform with punctilio, convert back to Markdown.)
Other typography libraries take one of two approaches, both with drawbacks.
String-based libraries (like smartypants) transform plain text but are unaware of HTML structure. If you concatenate text from <em>Wait</em>..., transform it into Wait…, and then try to convert back—you've lost track of where the </em> belongs.
AST-based libraries (like rehype-retext) process each text node individually, preserving structure but losing cross-node information. A quote that opens inside <em>"Wait</em> and closes outside it ..." spans two text node. Processed independently, the library can't tell whether the final " is opening or closing, because it never sees both at once.
punctilio introduces separation boundaries to get the best of both worlds:
Flatten the parent container's contents to a string, delimiting element boundaries with a private-use Unicode character (U+E000) to avoid unintended matches.
Every regex allows (and preserves) these characters, treating them as boundaries of a “permeable membrane” through which contextual information flows. For example, .U+E000.. still becomes …U+E000.
Rehydrate the HTML AST. For all k, set element *k’*s text content to the segment starting at separator occurrence k.
import { transform, DEFAULT_SEPARATOR } from 'punctilio'
const sep = DEFAULT_SEPARATOR transform("Wait${sep}") // → “Wait”${sep} // The separator doesn’t block the information that this should be an end-quote!
punctilio validates the output by ensuring the separator count remains the same.
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)
.use(rehypeStringify)
.process('<p><em>"Wait</em>..." -- she said</p>')
// → <p><em>“Wait</em>…”—she said</p>
// The opening quote inside <em> and the closing quote outside it
// are both resolved correctly across the element boundary.
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.
Fully general prime mark conversion (e.g. 5'10" → 5′10″) requires 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.
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.
While Claude is the number one contributor to this repository, that’s because Claude helped me port my existing code and added some features. The core regular expressions (e.g. dashes, quotes, multiplication signs) are human-written and were quite delicate. Those numerous commits don’t show in this repo’s history.
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.
Pretty good at making your text pretty. The most feature-complete and reliable English micro-typography package—transforms plain ASCII into typographically correct Unicode, even across HTML element boundaries.
Smart quotes · Em/en dashes · Ellipses · Math symbols · Legal symbols · Arrows · Primes · Fractions · Superscripts · Ligatures · Non-breaking spaces · HTML-aware · Bri’ish localisation support
Why punctilio?
As far as I can tell,
punctiliois the most reliable and feature-complete. I builtpunctiliofor my website. I wrote[1] 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.I tested
punctilio1.7.13 againstsmartypants0.2.2,tipograph0.7.4,smartquotes2.3.2,typograf7.6.0, andretext-smartypants6.2.0.[2] These other packages have spotty feature coverage and inconsistent impact on text. For example,smartypantsmishandles quotes after em dashes and lacks multiplication sign support.smartypantspunctilioMy
benchmark.mjsmeasures 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.punctiliotipographtypografsmartquotessmartypantsretext-smartypantspunctiliosmartypantstipographsmartquotestypograf© 2004
Known limitations of
punctilio'99 but 5' clearance5'not converted to5′«Bonjour»« Bonjour »Test suite
Setting aside the benchmark,
punctilio’s test suite includes 1,100+ tests at 100% branch coverage, including edge cases derived from competitor libraries (smartquotes,retext-smartypants,typograf), and the Standard Ebooks typography manual. Further, all transformations are stable when applied multiple times.Works with HTML DOMs via separation boundaries
Perhaps the most innovative feature of the library is that it properly handles DOMs! (This means it'll also work on Markdown: convert to HTML, transform with
punctilio, convert back to Markdown.)Other typography libraries take one of two approaches, both with drawbacks.
smartypants) transform plain text but are unaware of HTML structure. If you concatenate text from<em>Wait</em>..., transform it intoWait…, and then try to convert back—you've lost track of where the</em>belongs.rehype-retext) process each text node individually, preserving structure but losing cross-node information. A quote that opens inside<em>"Wait</em>and closes outside it..."spans two text node. Processed independently, the library can't tell whether the final"is opening or closing, because it never sees both at once.punctiliointroduces separation boundaries to get the best of both worlds:U+E000) to avoid unintended matches..U+E000..still becomes…U+E000.punctiliovalidates the output by ensuring the separator count remains the same.For
rehype/unifiedpipelines, use the built-in plugin which handles the separator logic automatically:Options
punctiliodoesn'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 = truecan 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.5'10"→5′10″) requires semantic understanding to distinguish from closing quotes (e.g."Term 1"should produce closing quotes).punctiliocounts quotes to heuristically guess whether the matched number at the end of a quote (if not, it requires a prime mark). Other libraries liketipograph0.7.4 use simpler patterns that make more mistakes.americanstyle follows the Chicago Manual of Style:britishstyle follows Oxford style:punctiliois idempotent by design:transform(transform(text))always equalstransform(text). If performance is critical, setcheckIdempotency: falseto skip the verification pass.Feedback welcome
If you run into bugs, please create an issue! You can read about my other open-source projects on my website.
While Claude is the number one contributor to this repository, that’s because Claude helped me port my existing code and added some features. The core regular expressions (e.g. dashes, quotes, multiplication signs) are human-written and were quite delicate. Those numerous commits don’t show in this repo’s history.
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.
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