Decode a message in base64
Decode a hidden Base64 message using a simple online decoder or step-by-step chart to reveal secret text and learn basic encoding principles.
Step-by-step guide to decode a message in base64
Understanding Base64: Encoding and Decoding Made Simple
Step 1
Look at the printed Base64 message and point to the full string of letters and symbols so you know where it starts and ends.
Step 2
Carefully copy the exact Base64 string onto a fresh line on your paper so you can work from a clean copy.
Step 3
Decide whether you will use an online Base64 decoder or decode by hand with the chart and tell an adult which way you picked.
Step 4
If you chose online, ask an adult to open a safe Base64 decoder page for you to use.
Step 5
Enter the Base64 string into the decoder input box by typing or pasting it in exactly as you copied it.
Step 6
Click the decoder’s "Decode" button and read the revealed text that appears in the output area.
Step 7
If you chose to decode by hand, use the Base64 chart to write the 6-bit number for each Base64 character under it on your paper.
Step 8
Join those 6-bit groups in order to make one long line of bits (a long string of 0s and 1s).
Step 9
Split the long bit string into groups of 8 bits and convert each 8-bit group into its decimal number using your chart.
Step 10
Use the decimal numbers to find matching ASCII letters or symbols and write each letter to reveal the hidden message.
Step 11
Take a photo or write a short note about your decoded message and share your finished creation on DIY.org
Final steps
You're almost there! Complete all the steps, bring your creation to life, post it, and conquer the challenge!
Help!?
What can we use instead of a printed Base64 message or a Base64 chart if those are hard to find?
Instead of a printed Base64 message you can display a clear screenshot on a tablet or phone to copy the exact Base64 string onto paper, and if you can't find a Base64 chart you can print one from a trusted educational site or skip the chart by using the online decoder step with an adult.
Why might the decoder give an error or a wrong-looking result, and how do we fix that?
If the online decoder returns an error or gibberish, check that you copied the exact Base64 string from the printed message (including any '=' padding and no extra spaces) into the decoder input box, or if decoding by hand recheck each Base64 character's 6-bit number and that your 8-bit groups line up correctly before converting to ASCII.
How can we adapt this activity for different ages like preschoolers, elementary kids, and teens?
For preschoolers have an adult open a safe Base64 decoder and let the child point to the revealed text, for elementary kids let them copy the string and paste into the decoder input box with guidance, and for teens have them decode by hand with the Base64 chart, join 6-bit groups to make the long bit string, and convert to ASCII themselves or write a small script to verify their result.
How can we extend or personalize the activity after decoding the message?
Make it a game by encoding your own short secret message with an online Base64 encoder, print that string for a friend to decode using the paper-and-chart steps, and then take a photo of the decoded message to share on DIY.org as suggested in the final step.
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base64 encoder and decoder
Quickly encode and decode Base64 text / strings
Facts about data encoding and decoding
🔢 ASCII turns letters and symbols into numbers (for example, 'A' is 65).
🧩 Base64 increases data size by about 33% — every 3 bytes become 4 Base64 characters.
🕵️ Base64 is encoding, not secret encryption — anyone who knows the method can decode it back to the original text.
📧 Base64 is often used with MIME to embed images and attachments inside emails and web data.
🔐 Base64 was created so binary files could be sent through text-only systems like early email.
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