The science
Learn while you browse.
Every hour you spend reading online is an opportunity to absorb vocabulary in context, the same way children learn their first language. LearnJargon turns your normal browsing habit into passive acquisition time.
What the system measures
Domain: nytimes.com · 6 minute session · stage-aware vocabulary feedback
Passive acquisition
How humans actually learn vocabulary
Decades of second-language acquisition research show that we don't learn vocabulary by memorising lists. We learn by encountering words in context, repeatedly, with just enough uncertainty to trigger memory consolidation.
Stephen Krashen's Comprehensible Input Hypothesis suggests that acquisition happens when we understand messages slightly above our current level, what he called “i+1”. LearnJargon operationalises this by replacing words you already understand with their foreign equivalents while keeping the text fully comprehensible.
Because you encounter words in the context of real articles you actually care about, the meaning sticks far better than flashcards or rote drills.
Progression system
The five stages of fluency
You advance when you consistently read substituted words without hovering. The system can tell when vocabulary has moved from effortful to automatic.
Core nouns: people, objects, places
At 5% substitution, one word in twenty is replaced. Only high-frequency, unambiguous nouns. Reading speed is virtually unaffected.
"The gato sat on the mat."
Nouns + descriptive adjectives
Adjectives join nouns at 12% replacement, which helps your brain form simple mental images in the target language.
"The pequeño gato slept quietly."
Nouns, adjectives + common verbs
Verbs are the backbone of any language. At 20% replacement, grammar begins to emerge without explicit study.
"The cat duerme in the pequeño chair."
Nouns, adjectives, verbs + structural words
Function words appear at 30% replacement. Sentence structure starts to feel natural and predictable.
"El cat duerme porque it is tired."
All word types + idiomatic phrases
At 40%+ with full phrase substitutions, you are reading genuinely bilingual text with strong contextual scaffolding.
"Por supuesto, the results were clear."
Session stats
Reading Speed Tracking
Your reading pace tells us what you know
The extension measures reading speed passively by tracking time-on-page and estimated text length. When a substitution causes your reading to slow significantly, measured by micro-pauses before a word, that is a signal that it is unfamiliar.
Combined with hover events, this creates a two-signal confidence score for each word in your vocabulary. The hover signal is explicit ("I didn't know this"); the WPM signal is implicit ("I slowed down").
Together they build an accurate model of your vocabulary without any active input from you.
Privacy by design
What the extension reads and does not
- ·Visible text nodes in article content
- ·Paragraph and heading elements
- ·Reading time estimates (time on page)
- ·Word hover events you trigger
- ·Form inputs or text fields
- ·Passwords or credentials
- ·URLs of banking / medical sites
- ·Personal data in any field
- ·Browser history