User Guide

How to Verify a Coin Flip (Provably Fair Mode)

Step-by-step instructions for verifying a CoinFlipTool result with Provably Fair Mode, including how to open fairness details and confirm that the outcome was generated correctly.

How to Verify a Coin Flip (Provably Fair Mode)

Green shield with a checkmark representing CoinFlipTool Provably Fair Mode verification.
CoinFlipTool takes fairness seriously, which is why Provably Fair Mode lets you verify that a coin flip was generated transparently and not controlled behind the scenes.

CoinFlipTool's Provably Fair Mode makes every flip fully transparent. Each flip includes:

  • A local device seed
  • A public randomness beacon from drand
  • A combined string
  • A SHA-256 hash
  • The result derived from that hash

You can verify each flip directly inside the app using the steps below.

Before You Verify: Make Sure Provably Fair Mode Is Enabled

If you do not see the next to flips on the History page, Provably Fair Mode is not active.

To enable it:

  1. Tap the Settings icon (gear symbol) in the top-right corner.
  2. Scroll to the Fairness section.
  3. Check whether Provably Fair Mode is listed.
  • If it appears, the mode is already active.
  • If you instead see Default Fair Mode, tap it.
  1. In the Fairness Configuration menu, select Provably Fair Mode.
  2. Tap Save.

After enabling, new flips will display the in the History page.

Step 1 — Open the Flip Details

Go to History, then navigate to the tab for the game mode you want to verify (such as "Single Flips", "Best of 3", etc.). Tap the next to the flip you want to verify.

Below is an example showing how fairness details appear:

Fairness details example

Step 2 — Copy the Combined String

The combined string always uses this format:

local_seed:public_beacon

Copy it exactly as displayed in the fairness details popup.

Step 3 — Compute the SHA-256 Hash

You can recompute the SHA-256 hash using any hashing tool or command-line method.

macOS / Linux

echo -n "COMBINED_STRING_HERE" | shasum -a 256

Windows PowerShell (OpenSSL)

echo -n "COMBINED_STRING_HERE" | openssl dgst -sha256

The resulting hash must match the one shown inside the fairness details.

Step 4 — Determine Heads or Tails from the Hash

CoinFlipTool derives the coin result using the first byte of the SHA-256 hash:

  • Even -> Heads
  • Odd -> Tails

To verify manually:

  1. Take the first two hex characters of the hash.
  2. Convert them to decimal.
  3. Check whether the number is even or odd.

If it matches the result shown in the app, the flip is verified.

When the Beacon Is Unavailable

If the drand network cannot be reached, CoinFlipTool temporarily switches to Default Fair Mode and displays a notice explaining that the flip used only local randomness.