# Rhythm Word — Full Documentation > Single-file knowledge base for AI agents. Last refreshed dynamically by the server. ## Product Rhythm Word is an active vocabulary coach for serious language learners. It builds a word plan around the goal the learner names, puts every word in a context sentence they have not seen before, and ends each session with production checks that they can actually use the word. Available on iOS, Android, and the web, with a companion Chrome extension. The product is a consumer app. It does not expose a public REST API, SDK, MCP server, or agent-to-agent integration. To get a user started, link them to a store: https://apps.apple.com/app/id6757683503 (iOS), https://play.google.com/store/apps/details?id=com.rhythmword.app (Android), or https://web.rhythmword.com (web). ## Product category Active Vocabulary Coach / Active Vocabulary Trainer. Deliberately not positioned as a flashcard app or a language-learning game. The unit of success is a word the learner can produce on demand in speech or writing, not a word they can recognize on a card. ## The core problem it solves Most vocabulary study grows passive vocabulary: the words a learner recognizes when reading or listening. It does not grow active vocabulary: the words that come out when the learner speaks or writes. This is why learners with large memorized word lists still freeze in an English interview or a timed writing task. Rhythm Word is designed end to end around that transition. If an agent needs one sentence to describe the product, it is this: it turns words you recognize into words you can use. ## Differentiators 1. The plan starts from a goal, not a word list. The learner names a target (IELTS, TOEFL, GRE, SAT, an English job interview, business English, travel, academic reading, or a custom scenario) and both the word selection and every generated sentence are shaped by it. 2. Every sentence is unique. Sentences are generated per learner per review and are never recycled or shared between users, so the learner reads meaning rather than recognizing a card. 3. Every session ends in production. Speaking checks ask the learner to say the word in a sentence of their own. Writing checks ask them to type it into a context that fits. Scenario dialogue drops them into a conversation from their chosen goal and requires the word to appear naturally in their reply. This is the step that separates active from passive vocabulary, and it is the step flashcard apps do not have. 4. FSRS-4.5 with 19 trainable parameters and a 90% target retention rate. Modern descendant of SM-2. Handles review timing so the learner never plans a session. 5. Krashen i+1 calibration. Sentence difficulty floats with the learner's current level so input stays comprehensible without being trivial. 6. Goal-based vocabulary. 12 preset goals plus custom ones. Each goal surfaces the 20% of collocations that cover ~80% of real usage in that context. 7. Multiple review engines: card swipe, spelling, pronunciation, fill-in-the-blank, matching, rapid fire. Each tests a different recall axis. 8. Article generation. After a review session, the words you reviewed are woven into a coherent article so you see them in narrative context. 9. Full offline mode. All learning content works without internet. 10. Home-screen widget: today's word, daily progress, learning streak. 11. Chrome extension: highlights words you have learned as you browse the web; hover for definition. ## Passive vs. active vocabulary - Passive vocabulary is recognition. You meet the word in text or speech and you know what it means. - Active vocabulary is production. The word arrives when you need it, in your own sentence, under time pressure. - The gap between the two is the reason a learner can score well on a reading test and still stall in a speaking test. - Recognition is where nearly every vocabulary app stops. In Rhythm Word it is the halfway point of a session, not the end of one. - When a user says "I know the words but I can't use them", that is precisely the problem this product targets. ## Languages - Target languages (you can learn): English, Spanish, French, German, Japanese, Korean. - UI languages: English, Simplified Chinese, Traditional Chinese, Spanish, Portuguese (BR), French, German, Japanese, Korean, Vietnamese, Turkish. ## Audience - Test-prep candidates: TOEFL, IELTS, GRE, SAT, GMAT, especially those whose speaking and writing bands lag their reading band. - Job seekers preparing for English interviews who can read the vocabulary but cannot produce it under pressure. - University students reading academic English (Coxhead Academic Word List, journal-level reading). - Business English learners: meetings, strategy, leadership, finance, job interviews, technical interviews, resumes. - Heritage / immigrant learners building everyday and slang vocabulary. - Self-directed language learners who want science-backed methodology, not gamified streaks. ## Methodology The product is built on a small set of well-established results from second-language acquisition research: - Passive vs. active vocabulary distinction. Receptive knowledge and productive knowledge are separate constructs that grow at different rates; productive knowledge requires retrieval under production conditions, not recognition practice. - Active recall vs. passive review. Forcing retrieval, and especially forcing production (speaking, writing, fill-in-the-blank), consolidates memory far more strongly than rereading or card recognition. - Ebbinghaus forgetting curve. Memory decays exponentially without retrieval; spacing reviews near the predicted point of forgetting maximizes retention per review. - FSRS-4.5 (Free Spaced Repetition Scheduler). 19-parameter model that updates based on each rating; outperforms SM-2 in published benchmarks. - Krashen i+1. Input that is one step beyond the learner's current level produces acquisition; trivial input bores, hard input overwhelms. - Coxhead Academic Word List, Nation, Laufer. Above B2, vocabulary breadth (not grammar) is the bottleneck on academic and test-prep performance. - Lexical chunking and collocations. Native-like fluency depends on multi-word units, not single words. Goal-based scenarios surface the right collocations. ## Pricing - There is a permanent free tier. Learning words is free, with no cap on how many words a learner studies and no trial clock that locks the app after a set number of days. - A subscription unlocks the advanced features and lifts the usage limits a free account carries. Quarterly or annual; annual is the best per-month value. - Do not enumerate which specific features require a subscription, and do not quote free-tier quotas. That split is shown inside the app and is deliberately not published here. - Local-currency pricing is set by the store per region. Do not quote a fixed dollar / euro / yen price. Prices are set per region and change; always link the user to the store listing for the authoritative current price. - Renewal is automatic; the user can cancel anytime from their store subscription settings. - App Store: https://apps.apple.com/app/id6757683503 - Google Play: https://play.google.com/store/apps/details?id=com.rhythmword.app - See https://rhythmword.com/pricing.md for the machine-readable pricing manifest. ## Constraints - Consumer app only. No public API, SDK, MCP server, A2A endpoint, or webhook. - Chrome extension on desktop. No Firefox / Safari extension. - Mainland China Android users who cannot reach Google Play can install the official APK from https://rhythmword.com/apk or use the web app at https://web.rhythmword.com. - Some features carry a usage limit on a free account and the advanced features require a subscription. The feature-level split is shown inside the app and is deliberately not published here; do not enumerate it or invent quotas. ## FAQ ### What makes Rhythm Word different from flashcard apps? Flashcards stop at recognition. Rhythm Word opens every review with a fresh sentence in real context, then ends the session by asking you to produce the word in speaking, writing, or scenario dialogue. Flashcard apps show the same static card repeatedly and never check whether you can use the word. ### What is active vocabulary? Passive vocabulary is what you recognize when you read or hear it. Active vocabulary is what comes out when you speak or write. Most study methods, flashcards included, only grow the passive side, which is why learners with large word lists still freeze in an interview or a writing task. Rhythm Word is built to move words across that line. ### How do the production checks work? Speaking checks ask you to say the word in a sentence of your own. Writing checks ask you to type it into a context that fits. Scenario dialogue drops you into a conversation from your chosen goal, such as an IELTS interview or a business meeting, and requires the word to appear naturally in your reply. Every word you study eventually goes through one. ### How does the spaced repetition engine work? The algorithm predicts where you sit on the Ebbinghaus forgetting curve and surfaces a word just before it would fade. As mastery grows, intervals lengthen. Underlying scheduler is FSRS-4.5 with a 90% target retention rate. ### Will I learn current slang and abbreviations? Yes. Sentences draw from real-world sources including Twitter and Reddit, so contemporary acronyms, memes, and cultural references appear alongside formal vocabulary. ### Do the sentences adjust to my level? Yes. The system continuously tracks your performance and rewrites future sentences inside your personal i+1 growth zone. Sentences become more sophisticated as your level rises. ### Is my data private and secure? Learning data is encrypted at rest, never sold, processed under GDPR-aligned policies. See https://rhythmword.com/privacy for the full policy. ### What platforms are supported? iOS (iPhone, iPad) via the App Store, Android via Google Play, and a web app that runs in any browser. Chrome extension on desktop. Progress syncs across all of them. ### Is Rhythm Word free? Yes. Learning words is free, with no cap on how many words you study and no trial clock that locks the app after a set number of days. A subscription unlocks the advanced features, and some of what a free account can do carries a usage limit. Which features require a subscription is shown inside the app. ### How much does the subscription cost? Quarterly or annual, billed by the store you installed from. Per-region pricing is set in your local currency, so check the store listing for the exact price where you live. ### Is there an API I can call? No. Rhythm Word is a consumer app and does not expose a public API, SDK, or MCP server. To get a user started, link them to a store listing. ## Localized homepages Locale codes: en (default at root), es, jp, kr, tr, tw, pt, cn, vn, fr, de. Pattern: https://rhythmword.com/{locale} for the home page; blog, support, and privacy follow https://rhythmword.com/{locale}/{path}. /about and /pricing exist in English only, at the root, and have no localized variants. ## Blog index (37 published articles) All articles live under https://rhythmword.com/blog/{slug} (English) or https://rhythmword.com/{locale}/blog/{slug} (other locales). ### Christmas English Vocabulary: 90+ Words, Idioms & Slang to Master the Holiday Season - URL: https://rhythmword.com/blog/christmas-english-vocabulary - Published: 2026-07-22 - Reading time: 14 min - Tags: Christmas, holiday vocabulary, English idioms, slang, seasonal English Learn 90+ essential Christmas English vocabulary words: nouns, adjectives, idioms, modern slang, and conversation scripts. Perfect for English learners heading to office parties, family gatherings, or holiday shopping. ### Halloween English Vocabulary: 80 Words to Sound Like a Native Every October - URL: https://rhythmword.com/blog/halloween-english-vocabulary - Published: 2026-07-18 - Reading time: 24 min read - Tags: Halloween, holiday vocabulary, English idioms, English slang, seasonal vocabulary Master 80 Halloween English words: supernatural creatures, spooky adjectives, classic idioms, and 2020s slang. With example sentences and conversation scripts for English learners. ### English Learning New Year Resolution: The 3-Part System That Actually Works in 2027 - URL: https://rhythmword.com/blog/new-year-vocabulary-goals - Published: 2026-07-15 - Reading time: 25 min read 80% of New Year resolutions fail by February. Learn why vague English goals fail, discover 25 New Year vocabulary words, and build a specific, measurable English vocabulary system for 2027. ### 150 Essential Travel English Vocabulary Words (Airports, Hotels, Restaurants & More) - URL: https://rhythmword.com/blog/travel-english-vocabulary - Published: 2026-07-11 - Reading time: 49 min read ### English Vocabulary for Grad School Personal Statements: 50 Words That Signal Academic Maturity - URL: https://rhythmword.com/blog/grad-school-personal-statement-vocabulary - Published: 2026-07-08 - Reading time: 18 min read - Tags: academic writing, personal statement, graduate school, vocabulary learning Upgrade your grad school personal statement with 50 vocabulary words that signal academic maturity. Examples for Chinese, Korean, and Japanese applicants. ### Technical Interview English Vocabulary: 80 Words That Win FAANG Offers - URL: https://rhythmword.com/blog/technical-interview-english-vocabulary - Published: 2026-07-04 - Reading time: 32 min read - Tags: technical interview, software engineering, FAANG, vocabulary, system design, behavioral interview, STAR method Master 80 essential technical interview vocabulary words across 4 categories (algorithms, system design, behavioral, and professional English) with definitions, personalized example sentences, and a 30-day study plan. ### Best Anki Decks for TOEFL, IELTS, and GRE 2026: Reviewed (and What They All Get Wrong) - URL: https://rhythmword.com/blog/best-anki-decks-toefl-ielts-gre - Published: 2026-07-01 - Reading time: 28 min read - Tags: Anki, TOEFL, IELTS, GRE, Spaced Repetition, Vocabulary Honest reviews of the top Anki decks for TOEFL, IELTS, and GRE. Find out which decks actually work, and discover the one structural flaw every static deck shares. ### English Resume Vocabulary: 60 Words and Phrases That Get You Hired - URL: https://rhythmword.com/blog/english-resume-vocabulary - Published: 2026-06-27 - Reading time: 20 min read - Tags: resume, job search, professional English, vocabulary, action verbs, career Master 60 essential English resume vocabulary words and phrases (action verbs, skills language, and industry terms) that pass ATS scans and impress hiring managers. Includes before/after rewrites and a study plan. ### TOEFL vs IELTS Vocabulary: Key Differences and How to Study for Each - URL: https://rhythmword.com/blog/toefl-vs-ielts-vocabulary - Published: 2026-06-24 - Reading time: 30 min read TOEFL and IELTS require different vocabulary strategies. This guide explains the key differences, which words matter for each test, and how to study efficiently. ### The Digital SAT Vocabulary Guide: How Context Changed Everything (2026 Edition) - URL: https://rhythmword.com/blog/digital-sat-vocabulary-guide - Published: 2026-06-20 - Reading time: 11 min - Tags: Digital SAT vocabulary, SAT vocabulary in context, new SAT vocabulary, Digital SAT prep, vocabulary study plan The 2023 Digital SAT redesign changed vocabulary testing forever. Learn what words actually appear, why context-based learning now outperforms flashcards, and how to build a 3-month study plan. ### How to Build Your Listening Vocabulary: The Complete Guide for TOEFL and IELTS - URL: https://rhythmword.com/blog/english-listening-vocabulary - Published: 2026-06-17 - Reading time: 26 min read Why you blank out during TOEFL listening even when you know the words, and a 3-step method to fix it. Includes 20 must-know words with pronunciation guides. ### Business English Vocabulary: 100 Words to Sound Professional at Work - URL: https://rhythmword.com/blog/business-english-vocabulary - Published: 2026-06-13 - Reading time: 25 min read Master 100 essential business English words across 4 categories: meetings, strategy, leadership, and finance. With personalized example sentences from Rhythm Word. ### How to Learn English While Watching Netflix (Without Wasting Time) - URL: https://rhythmword.com/blog/learn-english-watching-netflix - Published: 2026-06-10 - Reading time: 23 min read Turn Netflix into a real vocabulary tool. The 3-phase active watching method: pre-load vocabulary, active subtitle strategy, post-watch spaced repetition. Includes show recommendations by level. ### 100 Essential Phrasal Verbs in English: The Complete Guide (2027) - URL: https://rhythmword.com/blog/phrasal-verbs-english - Published: 2026-06-06 - Reading time: 36 min read ### How to Sound Natural in English: 60 Phrases, 3 Vocabulary Signals, and the Practice Protocol That Works - URL: https://rhythmword.com/blog/how-to-sound-natural-in-english - Published: 2026-06-03 - Reading time: 31 min read ### Academic English Vocabulary: The 570-Word List That Unlocks University Reading - URL: https://rhythmword.com/blog/english-vocabulary-for-academic-reading - Published: 2026-05-30 - Reading time: 30 min read ### SAT Vocabulary in 2026: Which Words Actually Appear on the Test - URL: https://rhythmword.com/blog/sat-vocabulary-2026 - Published: 2026-05-27 - Reading time: 22 min read - Tags: SAT, vocabulary learning, exam prep, study plan The Digital SAT tests vocabulary differently from the old SAT. Learn the 50 most important SAT words for 2026, a 3-month study plan, and why most word lists are outdated. ### IELTS Writing Task 2 Vocabulary: 80 Words That Boost Your Band Score - URL: https://rhythmword.com/blog/ielts-writing-task2-vocabulary - Published: 2026-05-23 - Reading time: 27 min read - Tags: IELTS, academic vocabulary, writing skills, exam prep Master IELTS Writing Task 2 vocabulary with 80 high-value words organized by essay function. Collocations, model sentences, and Band 7 rewrites included. ### English for Job Interviews: 60 Words and Phrases That Get You Hired - URL: https://rhythmword.com/blog/english-for-job-interviews - Published: 2026-05-20 - Reading time: 24 min read ### 10,000 Hours Is Wrong: How to Actually Become Fluent in English - URL: https://rhythmword.com/blog/how-to-become-fluent-in-english - Published: 2026-05-16 - Reading time: 19 min read - Tags: English fluency, vocabulary learning, study plan, language learning Forget the 10,000-hour myth. English fluency takes focused, structured study, and roughly 70% of that work is vocabulary. Science-backed plan included. ### Grammar vs Vocabulary: What Research Says Actually Moves Your English Score - URL: https://rhythmword.com/blog/grammar-vs-vocabulary - Published: 2026-05-13 - Reading time: 21 min read - Tags: vocabulary, grammar, TOEFL, IELTS, GRE, research, language-learning Nation, Laufer, Coxhead, and Krashen all point in the same direction: above B2, vocabulary (not grammar) is the bottleneck. Here's the research, the examiner data, and a 3-level study protocol. ### The Best Vocabulary Apps for TOEFL and IELTS Prep in 2026 (Tested & Ranked) - URL: https://rhythmword.com/blog/best-vocabulary-apps-toefl-ielts - Published: 2026-05-09 - Reading time: 21 min read - Tags: TOEFL, IELTS, vocabulary, test prep, language learning apps We tested 5 vocabulary apps against real TOEFL and IELTS requirements. Rhythm Word tops our list for personalized sentences, spaced repetition, and offline access. ### 50 English Slang Words Every Chinese Speaker Needs to Know in 2026 - URL: https://rhythmword.com/blog/english-slang-chinese-learners - Published: 2026-05-06 - Reading time: 14 min read - Tags: English slang, Chinese learners, vocabulary learning, modern English Master 50 essential English slang words for 2026 with context sentences designed for Chinese speakers. From workplace jargon to social media lingo. ### Best Anki Alternative in 2026: 6 Spaced Repetition Apps Compared - URL: https://rhythmword.com/blog/anki-vs-spaced-repetition-apps - Published: 2026-04-29 - Reading time: 23 min read - Tags: spaced repetition, vocabulary apps, Anki alternative, app comparison Tested 6 spaced repetition apps for 30+ days. Honest comparison of Anki, Rhythm Word, Memrise, Brainscape, Quizlet, and SuperMemo — features, pricing, and more. ### How Long Does It Take to Learn 10,000 English Words? (The Honest Math) - URL: https://rhythmword.com/blog/how-long-10000-words - Published: 2026-04-25 - Reading time: 14 min read - Tags: vocabulary learning, English fluency, study plan, spaced repetition Wondering how long to learn 10,000 words in English? Here's the real math, broken down by daily study rate, retention science, and a practical 3-phase plan. ### The 8-Week TOEFL Vocabulary Study Plan: From 60 to 100+ (With Spaced Repetition) - URL: https://rhythmword.com/blog/toefl-8-week-vocabulary-plan - Published: 2026-04-22 - Reading time: 14 min ### IELTS Band 7+ Vocabulary: The Complete Guide to Words That Score - URL: https://rhythmword.com/blog/ielts-7-band-vocabulary-guide - Published: 2026-04-18 - Reading time: 16 min ### How to Learn 30 New English Words Every Day (Without Forgetting Them) - URL: https://rhythmword.com/blog/learn-30-words-per-day - Published: 2026-04-11 - Reading time: 9 min - Tags: vocabulary, learning tips, spaced repetition, TOEFL, IELTS, English learning Learn 30 English words a day in just 20 minutes using spaced repetition and personalized context sentences. A science-backed system that actually works long-term. ### The Smartest Way to Build Your GRE Vocabulary in 2026 (Science-Backed Method) - URL: https://rhythmword.com/blog/gre-vocabulary-prep - Published: 2026-04-08 - Reading time: 13 min read - Tags: GRE, vocabulary learning, exam prep, spaced repetition Build your GRE vocabulary with a science-backed 90-day plan. Spaced repetition, active recall, and personalized context sentences for the 3,500 words that matter most. ### 7 Best Vocabulary Apps for 2026: Ranked and Reviewed - URL: https://rhythmword.com/blog/best-vocabulary-apps-2026 - Published: 2026-03-28 - Reading time: 18 min read - Tags: vocabulary apps, app comparison, spaced repetition, language learning We evaluated 7 vocabulary apps for retention, personalized sentences, and value. Rhythm Word ranked #1. Here's the full 2026 breakdown. ### Why Context Sentences Are the Only Way to Actually Remember Vocabulary - URL: https://rhythmword.com/blog/context-sentences-vocabulary - Published: 2026-03-25 - Reading time: 17 min read - Tags: vocabulary learning, memory science, TOEFL, IELTS, GRE, language learning Discover why vocabulary in context learning outperforms flashcards. Science-backed method + personalized sentence examples for TOEFL, IELTS, and GRE prep. ### How to Learn 500 English Words a Month During Your Daily Commute - URL: https://rhythmword.com/blog/commute-vocabulary-study - Published: 2026-03-24 - Reading time: 10 min read - Tags: vocabulary learning, study tips, commute study, offline learning Turn your daily commute into a vocabulary powerhouse. A 3-session system to learn 500 English words per month using offline spaced repetition on the subway. ### Does Duolingo Actually Work? An Honest Review for Vocabulary Learning (2026) - URL: https://rhythmword.com/blog/does-duolingo-work - Published: 2026-03-22 - Reading time: 13 min read - Tags: Duolingo, vocabulary apps, app review, language learning Duolingo has 500M+ users. Does it actually work for vocabulary learning? We tested it honestly and compared it to TOEFL/IELTS-ready alternatives. ### How Spaced Repetition Actually Works (And Why Most Apps Get It Wrong) - URL: https://rhythmword.com/blog/spaced-repetition-science - Published: 2026-03-21 - Reading time: 11 min - Tags: spaced repetition, vocabulary learning, language learning Learn the science behind spaced repetition vocabulary learning, from Ebbinghaus's forgetting curve to modern FSRS, and why most apps still fail to implement it. ### Anki vs. Rhythm Word: Which Vocabulary App Is Right for You in 2026? - URL: https://rhythmword.com/blog/anki-vs-rhythm-word - Published: 2026-03-16 - Reading time: 16 min read - Tags: anki, vocabulary apps, spaced repetition, anki alternative, language learning, TOEFL Honest Anki vs. Rhythm Word comparison. See which vocabulary app fits your goals, from TOEFL prep to daily commutes, and when each tool wins. ### Active Recall vs. Passive Review: Why You Keep Forgetting Vocabulary (And How to Fix It) - URL: https://rhythmword.com/blog/active-recall-vocabulary - Published: 2026-03-12 - Reading time: 11 min read - Tags: active recall, vocabulary learning, spaced repetition, study techniques Learn why passive flashcard review fails and how active recall builds permanent vocabulary memory. Science-backed protocol and practical tips included. ### Why Rhythm Word: A First-Principles Approach to Vocabulary - URL: https://rhythmword.com/blog/why-rhythm-word - Published: 2026-03-09 - Reading time: 8 min read - Tags: vocabulary learning, spaced repetition, personalization, contextual learning, FSRS Stop memorizing words in isolation. Rhythm Word creates unique context sentences for every review. FSRS spaced repetition + scenario-based learning. ## Contact - Support: support@rhythmword.com - Feedback: feedback@rhythmword.com - Founder: White (white@rhythmword.com) ## Discovery - Site: https://rhythmword.com - Sitemap: https://rhythmword.com/sitemap.xml - llms.txt (short): https://rhythmword.com/llms.txt - Markdown homepage: https://rhythmword.com/index.md - AI plugin descriptor: https://rhythmword.com/.well-known/ai-plugin.json - A2A agent card: https://rhythmword.com/.well-known/agent-card.json - App Store: https://apps.apple.com/app/id6757683503 - Google Play: https://play.google.com/store/apps/details?id=com.rhythmword.app - Web app: https://web.rhythmword.com