Begin with the creator’s own reconstruction account
In the original 2015 Determination project, Haley Wakamatsu describes making two fonts to mimic Undertale’s in-game text after finding an existing candidate inaccurate. That is the maker’s design motivation, not confirmation that the reconstruction is the game’s original production file. The Unofficial Undertale Web Fonts project names Determination Mono, credits Wakamatsu and separately offers Determination Sans. Keep this suite separate from logo-lettering projects and unrelated fonts with the same generic name.
Match the edition before judging its apparent pixel size
Wakamatsu’s account recommends 10pt, approximately 13.333px, for the desktop version and 16px, or 12pt, for a separately exported web version, explaining that the em-size definition differs. Do not assume identical numerical sizes produce identical results across those editions. Record the exact version and test its own recommended starting size before deciding whether the face is too small or blurry. The web-kit page is independently maintained and explicitly unofficial; it does not turn every bundled face into an original game resource or establish unrestricted rights for unrelated projects.
Compare a short original dialogue panel
Write a new two-sentence message with a question, a number and punctuation, using no game dialogue or character artwork. Keep the panel dimensions and padding fixed while comparing sizes for the chosen edition. Check the baseline, line break and repeated narrow letters in the rendered output; then inspect the same panel at its intended display scale. Press Start 2P below is an independent comparison, not Determination Mono or its Sans companion. The homepage copy-and-paste styles transform Unicode characters rather than embedding this pixel font or preserving its rendering dimensions.
Your questions, answered.
Is Determination Mono documented as the original Undertale production font?
The creator describes a font suite made to mimic the game’s text. The separate web-kit project explicitly calls itself unofficial.
Why do the documented desktop and web starting sizes differ?
The creator explains that the separately exported versions use different em-size definitions, recommending 10pt for desktop and 16px for the web version.
Sources & background
Sources supporting this page’s explanations. Practical examples are our editorial suggestions.