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Flip a Coin

Flip a Coin — Complete Documentation

Free online coin flipper by Uplup. Flip up to 1,000 coins at once with realistic 3D animations. Features weighted probability, streak tracking, standard deviation analysis, and CSV/TXT export.

Table of Contents

  1. Overview
  2. Getting Started
  3. Flipping Coins
  4. Customization
  5. Results & Statistics
  6. Animation & Rendering
  7. Live / Full-Screen Mode
  8. Saving Configurations
  9. Probability Education
  10. Platform Statistics
  11. API Reference
  12. FAQ

1. Overview

The Uplup Flip a Coin tool is a free, ad-free coin flipper with:

  • 1 to 1,000 coins per flip
  • 3 coin designs — realistic coin face images
  • 3 coin sizes — small, medium, large
  • Weighted probability — adjust heads/tails bias (0–100%)
  • Realistic 3D flip animation with bounce physics
  • Advanced statistics — streaks, standard deviation, deviation from expected
  • CSV and TXT export — download complete flip history
  • Flip goals — set a target number of flips and track progress
  • Save configurations — logged-in users can save setups to the cloud
  • Full-screen mode — presentation-ready live mode
  • Probability education — interactive lessons on fairness, gambler’s fallacy, and more

URL: uplup.com/flip-a-coin

2. Getting Started

  1. Visit uplup.com/flip-a-coin
  2. Click the coin or press Space to flip
  3. The coin animates and lands on Heads or Tails
  4. Results appear in the history table with timestamp
  5. Customize via the Coin Settings button

No account required. Settings persist in browser cookies for 365 days.

3. Flipping Coins

3.1 Basic Flip

Click the coin display or press Space to flip.

Flip flow:

  1. Click to trigger flip
  2. Coin spins with 3D rotation (3-7 full rotations)
  3. Random direction and random tilt (±10°)
  4. Easing: cubic ease-out for natural deceleration
  5. Bounce animation (3 phases: 15px → 10px → 5px)
  6. Result displayed (Heads or Tails)
  7. Result modal appears with outcome
  8. Result added to history table

Animation duration: 1 to 3.5 seconds per coin (randomized).

3.2 Multiple Coins (1–1,000)

Flip multiple coins simultaneously:

  • UI range: 1–100 coins (input + range slider in Customize modal)
  • Backend support: Up to 1,000 coins
  • All coins animate independently with randomized durations
  • Results show individual outcomes (e.g., “Heads, Tails, Heads, Tails, Heads”)
  • Result modal summarizes all outcomes

3.3 Keyboard Shortcuts

ShortcutAction
SpaceFlip coins
Ctrl + UUndo last flip
Ctrl + Shift + CClear all results (with confirmation)
EscExit full-screen mode

4. Customization

Open the Coin Settings modal via the button below the coin.

4.1 Coin Designs

3 coin design sets available:

SetDescription
Set 1Default coin design
Set 2Alternative coin design
Set 3Third coin design variant

Each set includes a heads image and a tails image stored on CDN (uplup-media.ams3.digitaloceanspaces.com/root/coins/).

Selected set shows a 4px coral (#E8604C) border. Hover shows a gray border.

4.2 Coin Size

SizePixel Dimension
Small75px
Medium200px (default)
Large300px

Button group selector with active state highlighted in coral.

4.3 Number of Coins

  • Text input and range slider (1–100)
  • Both inputs sync in real-time
  • Backend supports up to 1,000

4.4 Weighted Probability

Adjust the probability of landing on heads vs tails:

  • Slider range: 0% (always tails) to 100% (always heads)
  • Default: 50% (fair coin)
  • Labels: “Always Tails” | “Fair (50/50)” | “Always Heads”
  • Warning badge: “Weighted” appears when probability ≠ 50%
  • Tooltip: “Educational tool: Demonstrates probability concepts. Set to 50% for fair coin.”

Example settings:

ProbabilityBehavior
0%Always tails
25%~25% heads, ~75% tails
50%Fair coin (equal chance)
75%~75% heads, ~25% tails
100%Always heads

4.5 Flip Goal

Set an optional target number of flips:

  • Input field: enter a number (e.g., 100)
  • Progress display: “Progress: 42/100 (42%)”
  • Purely informational — does not prevent flipping beyond the goal

4.6 Title Display

Toggle Show Title to display the saved configuration name above the coin area.

5. Results & Statistics

5.1 Results Table

ColumnDescription
Flip #Sequential number (newest first)
Result“Heads” (blue) or “Tails” (red), comma-separated for multi-coin
TimeTimestamp (HH:MM:SS)
ActionsDelete button (trash icon)

Reverse-chronological order. Each row individually deletable.

5.2 Heads/Tails Summary

Always-visible large display:

┌─────────────┬──────────────┐
│   Heads      │    Tails     │
│   {count}    │    {count}   │
│   {percent}% │    {percent}%│
└─────────────┴──────────────┘

5.3 Advanced Statistics

Displayed in a coral-bordered box when flips > 0:

StatDescriptionFormula
Longest Heads StreakMaximum consecutive headsScan for longest run
Longest Tails StreakMaximum consecutive tailsScan for longest run
Expected Heads (50%)Theoretical count at 50%total × 0.5
Deviation from ExpectedHow far actual differs|heads − expected|
Standard DeviationVariation measure√(p × (1−p) / n) where p=0.5

5.4 Export (CSV & TXT)

CSV Export (coin-flip-results-YYYY-MM-DD.csv):

Flip #,Result,Timestamp
1,"Heads","3/25/2026, 2:45:30 PM"
2,"Tails","3/25/2026, 2:45:32 PM"

Summary
Total Flips,50
Heads,24 (48.0%)
Tails,26 (52.0%)

Advanced Statistics
Longest Heads Streak,5
Longest Tails Streak,4
...

TXT Export (coin-flip-results-YYYY-MM-DD.txt):

COIN FLIP RESULTS
═══════════════════════════════════════
Flip #1: Heads (3/25/2026, 2:45:30 PM)
Flip #2: Tails (3/25/2026, 2:45:32 PM)
═══════════════════════════════════════
SUMMARY
Total Flips: 50
Heads: 24 (48.0%)
Tails: 26 (52.0%)

Advanced Statistics:
  Longest Heads Streak: 5
  Longest Tails Streak: 4
  ...
Generated on: 3/25/2026, 3:00:00 PM

6. Animation & Rendering

3D Coin Flip Physics

Each coin is an HTML div with two image sides using CSS 3D transforms:

  • Heads side: rotateY(0deg) — visible at 0°, 360°, 720°…
  • Tails side: rotateY(180deg) — visible at 180°, 540°…

Spin Phase (1–3.5 seconds):

  • Random duration per coin: 1000 + Math.random() × 2500ms
  • Random spins: 3-7 full rotations (360° each)
  • Random direction: clockwise or counter-clockwise
  • Random tilt: ±10° on X-axis for wobble
  • Easing: cubic ease-out (1 − (1−t)³)
  • Final rotation determines result (even = heads, odd half-rotation = tails)

Bounce Phase (400–800ms):

  • 3 decreasing bounces: 15px → 10px → 5px
  • Sine wave trajectory for smooth arc
  • Scale decrease during bounce
  • Returns to original position

Performance:

  • requestAnimationFrame for smooth 60fps
  • CSS transform-style: preserve-3d
  • CSS backface-visibility: hidden on each side
  • All coins start simultaneously, finish at different random times

7. Live / Full-Screen Mode

Enter presentation mode via the Full Screen button.

Features:

  • Coin centered on screen (z-index: 9999)
  • All UI hidden (navigation, sidebar, results)
  • Flip counter displayed top-left
  • Title displayed top-center (if configured)
  • Intercom widget hidden
  • Close button top-right
  • Escape key to exit

Ideal for: classroom demonstrations, decision-making presentations, probability experiments.

8. Saving Configurations

Cookie Persistence (All Users)

Settings automatically saved to browser cookies (365-day expiry):

  • Coin set, coin size, number of coins
  • Complete flip history
  • Title and show title toggle

Server Persistence (Logged-In Users)

  • Auto-save after each flip
  • Manual save via the Save button
  • Load via URL parameter: ?config_id=abc123
  • Delete configurations (soft delete)

Save flow for new users:

  1. Click Save → Unsaved Work Modal appears
  2. “Save My Coin (Sign Up Free)” → redirects to Cognito signup
  3. After auth callback, config auto-saves with fc_save_after_login cookie flag

9. Probability Education

Six interactive educational cards:

TopicKey Concept
Law of Large NumbersAs flips increase, actual % converges to 50%. Try 10 → 100 → 1,000 flips.
Gambler’s FallacyEach flip is independent. 10 heads in a row still has 50% chance for the next flip.
Expected vs. ActualFair coin expects 50% heads. 45-55 heads in 100 flips is perfectly normal.
Standard DeviationMeasures variation. Formula: √(p × (1−p) / n). Lower = closer to expected.
Streaks & PatternsLong streaks naturally occur in randomness. 5-7 streak in 100 flips is normal.
Weighted ProbabilityAdjust bias (0-100%) to demonstrate unfair coins. 70% heads ≈ 70 heads in 100 flips.

Use case banner:

  • Students & Teachers — classroom probability demonstrations
  • Researchers — simulations, hypothesis testing
  • Critical Thinking — understanding cognitive biases
  • Data Science — sampling distributions, confidence intervals

10. Platform Statistics

The landing page displays global usage stats (cached every 5 minutes):

StatDescription
Coin Flips (24h)Flip actions in the past 24 hours
Coin Flips (30d)Flip actions in the past 30 days
Individual Coins Flipped (24h)Total coins (across all multi-coin flips) in 24h
Individual Coins Flipped (30d)Total coins in 30 days

Tab selector switches between 24-hour and 30-day views.

11. API Reference

Endpoints

MethodRouteAuthDescription
POST/api/v2/coin/flipNoneFlip coins (cryptographic random)
POST/api/v2/coin/configurationsRequiredSave/update configuration
GET/api/v2/coin/configurations/{id}RequiredLoad configuration
POST/api/v2/coin/configurations/deleteRequiredDelete configuration
POST/api/v2/coin/trackNoneAnonymous analytics tracking
GET/api/v2/coin/statsNoneCached platform statistics

Flip Coins (POST /api/v2/coin/flip)

// Request
{ "num_flips": 5 }

// Response
{
  "success": true,
  "data": {
    "results": ["heads", "tails", "heads", "tails", "heads"],
    "summary": { "heads": 3, "tails": 2, "total": 5 },
    "timestamp": "2026-03-25T14:30:00.000Z"
  }
}

Uses System.Security.Cryptography.RandomNumberGenerator.GetInt32(2) — cryptographically secure. 0 = heads, 1 = tails.

12. FAQ

Q: Is the coin flipper free?
A: Yes. 100% free, no ads, no signups, no limits.

Q: Is it truly random?
A: Yes. The backend uses System.Security.Cryptography.RandomNumberGenerator for cryptographically secure random results.

Q: How many coins can I flip at once?
A: Up to 100 in the UI, up to 1,000 via the API. Each coin flips independently with its own animation.

Q: What is weighted probability?
A: An educational feature that lets you bias the coin. Set to 70% and approximately 70% of flips will be heads. Useful for teaching probability concepts. Default is 50% (fair coin).

Q: Can I export results?
A: Yes. Export as CSV (for spreadsheets) or TXT (human-readable) with complete flip history, summary, and advanced statistics.

Q: Can I save my setup?
A: Yes. Create a free account to save configurations to the cloud. Without an account, settings persist in browser cookies for 365 days.

Q: Does it work on mobile?
A: Yes. Fully responsive with touch-friendly controls and works on all modern browsers.

Q: Can I set a flip goal?
A: Yes. Enter a target number in the Customize modal. Progress is tracked as a percentage (e.g., “42/100 — 42%”).

Q: What statistics are tracked?
A: Heads/tails count and percentage, longest heads streak, longest tails streak, expected heads at 50%, deviation from expected, and standard deviation.

This document covers every feature, option, and capability of the Uplup Flip a Coin tool as of March 25, 2026.