Calling Duolingo a flashcard app is a slight mischaracterization - it is more accurately described as a language gamification platform. But its vocabulary learning function competes directly with flashcard tools for the learner's study time, so the comparison is valid and useful.
This review compares Duolingo and Gridually specifically for vocabulary acquisition, ignoring Duolingo's grammar and speaking features to focus on the head-to-head that matters for vocabulary learners.
Duolingo gives learners essentially no control over their learning sequence. You progress through Duolingo's predetermined course, and the content you encounter is Duolingo's choice, not yours. This works for learners with no existing language knowledge and no specific vocabulary target - Duolingo's general vocabulary is a reasonable foundation. It fails for learners with specific goals: someone preparing for the DELE B2 exam, someone who needs vocabulary for their professional domain, or someone studying a dialect or regional variety that Duolingo's standardized courses do not cover. Gridually gives full control over what goes in each grid, enabling learners to match their study material precisely to their goals.
Duolingo uses a simplified spaced repetition system that flags words for review based on time since last encounter and performance history. The algorithm is less sophisticated than Anki's or Gridually's, which means it is less optimal at scheduling reviews to prevent forgetting. Gridually uses both spaced repetition intervals and spatial encoding - each word in a fixed grid position accumulates a positional memory alongside the lexical memory, providing two retrieval cues per word rather than one. Over a vocabulary set of several hundred words, this dual-encoding advantage compounds into meaningfully stronger retention than a simple interval-scheduled card queue.
For vocabulary acquisition specifically, Gridually is more efficient and produces stronger long-term retention than Duolingo. Duolingo's strengths - behavioral design, audio content, gamification, speaking practice - are largely outside the vocabulary flashcard comparison. Learners who want both habits and retention often run Duolingo alongside Gridually rather than choosing exclusively between them. Gridually's spatial encoding is based on memory research from the University of Chicago, University of Bonn, and Macquarie University.
Gridually replaces Duolingo's vocabulary review function better than it replaces Duolingo's grammar and speaking practice. Learners who use Duolingo primarily for vocabulary would get stronger retention results from Gridually. Learners who rely on Duolingo for grammar explanation and speaking practice would need additional resources beyond Gridually.
Duolingo supports over 40 languages. Gridually's language-specific grid packs are more limited currently, though the platform supports any language's vocabulary in custom grids. Popular learning languages have curated packs available.
Duolingo is effective for building a daily habit and covering A1-A2 vocabulary. Research on its effectiveness at higher proficiency levels is less favorable. Most serious language learners use Duolingo for consistency and supplement it with more rigorous tools for actual retention depth.