Pondr

Spaced repetition tools schedule reviews on fixed intervals that ignore individual learning behavior. Pondr personalizes the forgetting curve per user per concept from behavioral signals.

Knowledge graph canvas

A React Flow canvas where each concept is a node with a color-coded state:

Nodes are draggable and positions persist across sessions. A timeline scrubber replays learning history.

Hub-based learning

Searching a topic creates a Hub with its own knowledge subgraph, generated by Gemini plus live web research. Prior learning history and past hubs set per-concept difficulty (easy/intermediate/hard), with beginner concepts positioned left and advanced right.

Learning modes

Voice input

ElevenLabs STT (POST /api/speech/transcribe) on onboarding and canvas search. Text-to-speech via POST /api/speech/tts.

Google Calendar integration

Full OAuth 2.0 read/write. Gemini generates weekly study schedules from hubs, availability, and decay state, pushed as [Pondr] Study: <concept> events. Falls back to default free slots (8–10am, 2–4pm, 7–9pm) when unconnected.

Web search and scraping

Tavily for real-time search when generating hub graphs. Firecrawl for resource extraction.

Gamification

XP awards (video snippet +40, quick quiz +80, Feynman +120, Socratic round +150, full Socratic 3+ rounds +450, daily login +25, streak bonus +10 × streak_days). Six level tiers: Novice (0–1,000), Explorer (1,001–3,000), Pathfinder (3,001–8,000), Scholar (8,001–18,000), Master (18,001–35,000), Sage (35,001+). Eight achievements across Common, Rare, Epic, and Legendary rarities.

Data flow: register/login issues a JWT → onboarding saves prior learning history → topic search creates a Hub and generates its graph via Gemini plus web research → node interactions log learning events and award XP → the decay engine scores each node via XGBoost and updates node state → Gemini recommendations surface targeted YouTube clips and practice scenarios → Gemini generates a study schedule, optionally synced to Google Calendar.

Predicts retention R(t) for each user-concept pair: the probability the concept is still remembered at time t, range 0.0 to 1.0. Personalizes the Ebbinghaus stability parameter S from 10 behavioral features.

Feature importances

Performance

Training data

1,000 synthetic learner records generated with realistic behavioral distributions by backend/ml/generate_dataset.py. Trained by backend/ml/train_model.py, serialized to backend/ml/decay_model.joblib.

Edge cases

• days_since_review = 0 → return retention 1.0, skip model
• last_reviewed null → set days_since_review = 99, return retention 0.0
• review_count = 0 → skip model, return state red
• All predictions clipped to [0.0, 1.0]
• Model file missing → log warning, return 0.5 default

Nine routers. All endpoints except Auth and Health require Authorization: Bearer <token>.

MongoDB with Beanie ODM (async Pydantic documents).

• User: auth, profile (goal, background, prior_history, learner_type, has_onboarded), Google OAuth fields (google_id, access/refresh tokens, token expiry, calendar_connected), gamification (xp, level, level_title, streak_days, last_active_date, daily_xp, daily_xp_goal, achievements, skill_points)
• Hub: user_id, topic, title, created_at, last_accessed_at
• ConceptNode: user_id, hub_id, concept, domain, complexity_tier, dependency_depth, state, mode, mastery_score, stability_s, retention_rt, last_reviewed, review_count, canvas_x, canvas_y, difficulty_label
• LearningEvent: every interaction: view, rewatch, practice, feynman, snapshot, quiz
• Recommendation: Gemini recommendation for a node, with YouTube video ID and exact timestamp window
• KnowledgeEdge: directed edge between ConceptNodes, type prerequisite or related, scoped to a hub
• StudyPlan: weekly schedule with embedded StudySession objects and optional Google Calendar event IDs
• Achievement: unlock conditions and XP rewards
• GeminiRateLimit: per user per node, max 1 call per node per 6 hours

Google OAuth exchanges the auth code for Google tokens, links by google_id or email, stores the refresh token for Calendar access, and returns a Pondr JWT.