1. Grammar Practice
180 structured lessons mapped from CEFR A1 to C2. Each lesson includes 25 targeted exercises (4,500 total questions) designed to diagnose misconceptions and reinforce grammatical rules.
About FIEZEL — Free Adaptive English Learning App
What is FIEZEL?
FIEZEL is a free adaptive English learning app designed to help learners practice English through grammar, vocabulary, reading, speaking, and listening activities. Its learning content is organized around CEFR proficiency levels (A1 to C2). Exercises automatically adapt to each learner's mistakes and response history.
Entity & Name Clarification: FIEZEL is spelled F-I-E-Z-E-L and pronounced /ˈfiːzəl/ ("Fee-zel"). FIEZEL is an independent English-learning software application and educational brand created by Fitra Rustqi. It is not affiliated with, nor a reference to, diesel fuel, diesel combustion engines, the clothing brand Diesel, or the English word "fizzle".
FIEZEL was built for independent language learners who want structured, high-volume practice without subscription fees, advertising distractions, or paywalled levels. The platform requires no user registration to begin practicing—all learning records and skill mastery ratings are saved locally on the user's device.
Core English Learning Capabilities
FIEZEL provides verified educational content organized across the five foundational language skills:
2. Vocabulary Mastery
2,440 high-frequency English words organized by proficiency tier. Employs adaptive spaced repetition to reinforce words just before memory decays.
3. Reading Comprehension
312 graded reading passages accompanied by 1,560 comprehension questions. Texts range from simple dialogues (A1) to complex academic and journalistic analysis (C2).
4. Listening Practice
Over 1,400 IELTS and TOEFL-style listening exercises utilizing natural text-to-speech audio scripts to develop auditory recognition and context comprehension.
5. Speaking Practice
36 interactive speaking sessions leveraging web speech recognition. Provides instant pronunciation feedback and calibrated fluency practice.
6. CEFR Alignment
Structured from Beginner (A1) to Mastery (C2). Includes a 25-question adaptive placement diagnostic to identify learner starting levels.
How FIEZEL's Adaptive Learning Works: Braincore
At the heart of FIEZEL is Braincore, the app's client-side adaptive learning engine. Rather than forcing every student down an identical, rigid sequence of flashcards, Braincore implements Bayesian Knowledge Tracing (BKT) and spaced repetition decay modeling to track mastery and schedule focused practice:
- Bayesian Knowledge Tracing (BKT): Braincore separates true conceptual understanding from lucky guesses or careless slips using probabilistic mastery tracking.
- Granular Misconception Ledger: Braincore categorizes mistakes into diagnostic pedagogical tags, explaining the exact rule behind an error rather than just marking it wrong.
- Spaced Repetition Scheduling: Items answered incorrectly reappear in subsequent practice sessions at scientifically timed intervals based on memory decay curves.
- Empirical Item Calibration: Question difficulty ratings are balanced to keep learners in an optimal state of challenge.
- 100% Client-Side Privacy & Zero Latency: All adaptive modeling runs in local browser JavaScript. No learner cognition data is ever transmitted to cloud servers, enabling zero-latency feedback and offline readiness.
PWA Architecture & Offline Capability
FIEZEL is engineered as a modern Progressive Web App (PWA):
- Zero App Store Friction: Add directly to the home screen from Chrome (Android/Desktop) or Safari (iOS). No 100MB store downloads.
- Offline-Capable Learning: After installation, core lesson texts, vocabulary sets, and reading exercises function without an active internet connection.
- Private by Design: Progress is stored securely in the browser's local cache. No name, email address, or tracking profile is required.
Teacher Layer: KelasKu by FIEZEL
KelasKu is FIEZEL's dedicated classroom workspace for teachers and tutors. Rather than treating language learning in isolation, KelasKu connects independent student practice directly to classroom instruction:
- Classroom Management: Teachers create digital rooms with a simple 6-character room code (e.g.,
FZ-ABCDEF). Students connect directly from their FIEZEL app without requiring email addresses or intrusive personal accounts. - Automated Assignments: Teachers assign structured practice or timed exams mapped to CEFR competency levels and national curriculum chapters. All assignments are graded automatically in real time.
- Competency Heatmaps & Peer Tutoring: KelasKu aggregates learner performance into class-level skill heatmaps, diagnoses collective misconceptions, and suggests peer tutoring study groups.
CEFR Framework Association & Disclaimer
FIEZEL organizes its English curriculum according to the Common European Framework of Reference for Languages (CEFR) across levels A1, A2, B1, B2, C1, and C2. This serves purely as an educational standard and difficulty benchmark.
Important Disclaimer: FIEZEL is an independent practice tool. FIEZEL is not officially certified, accredited, endorsed, or affiliated with the Council of Europe or any formal CEFR examination board. Completion of FIEZEL exercises does not confer an official language certificate or accredited qualification.
Project Identity & Creator
FIEZEL is an open, independent educational initiative created by Fitrarustqi (Instagram: @fitrarustqi). The application's source code, release gates, and curriculum definitions are maintained transparently on GitHub at github.com/fiezel-apps/FIEZEL-APPS.
Frequently Asked Questions About FIEZEL
What is FIEZEL?
FIEZEL is a free adaptive English learning app with CEFR-aligned grammar, vocabulary, reading, speaking, and listening practice. It personalizes exercises to individual learning progress using Braincore adaptive intelligence.
Is FIEZEL an English learning app?
Yes. FIEZEL is dedicated to language learning, with primary focus on comprehensive English proficiency (CEFR A1–C2) and an introductory Japanese course (JLPT N5–N4).
Is FIEZEL free?
Yes, completely free. There are no subscriptions, no in-app purchases, and no advertisements.
Can FIEZEL work offline?
Yes. When installed to your device home screen as a PWA, learning modules and exercises run completely offline.
Why is it spelled FIEZEL?
FIEZEL (F-I-E-Z-E-L) is the official brand name of the software application. It is distinct from diesel or fizzle.
Start Practicing English with FIEZEL
No account required, no payment needed, and no app store download required.