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This article is about bugs in Scratch itself. For bugs in computer software, see Bug.

There are many notable bugs in Scratch. Some may just be graphical, some might impact coding, some might make text missing and some might show extra things. There are many minor bugs, but they are often fixed. However, some of them may impact the Scratch editor or website significantly.

Current Bugs

Mailbox Bug

In the Scratch website, the mailbox may show "0 Messages" rather than no number. A possible reason for this was that the mailbox did have messages but just showed the number '0'.


Wrong Font Bug

In the Paint Editor after the release of Scratch 3.0, sometimes the Sans Serif font displays as a larger Serif font. There is no known cause and solution for this bug, but the workaround is to use the Chinese, Japanese, or Korean fonts instead, as they all look very similar to the Sans Serif font. This is very similar to the Sans Serif bug (backdrop selector).

No Last Post Bug

Main article: No Last Post

In May 2017, when spammers were active, on some occasions the "last post" field next to a subforum description would be missing. Though it died down after a while, later posts in the affected forums seemed to bring it back. The reason why this happens remains unknown.[1]

Disappearing Comment Bug

Main article: Disappearing Comment Bug

Mainly found in Scratch 3.0, this bug causes profile, project, or studio comments to not show when attempting to view it. Sometimes, when the message for the comment is clicked, the comment section will not load. Then, if a user tries to view the page where the comment is without the direct comment link, the comment will not be shown. This can cause the inability to view, reply, delete, or report the comment. To fix this, do a hard refresh.[citation needed]

Trending Glitch

Main article: Trending Glitch

In Scratch 3.0, the trending glitch is a way of getting one's project shown in the trending category of Explore without the project actually qualifying for "trending" status. Unsharing and then resharing projects utilizes the glitch by making the Scratch website believe that the reshared project received however many loves and favorites the project in question had before the reshare immediately as it was reshared when in fact the project had already received those loves and favorites before it was even shared. As a result, the project is mistakenly shown as "trending."

Percent Custom Block

The blocks bunched up after naming a custom block "%"

In the Scratch 3.0 project editor, naming a custom block "%" will result in Scratch not letting one press "OK." If one presses "cancel" after that, all the blocks in the Block Palette will be bunched up and display in the same location. This bug can be fixed by going to a different sprite or leaving the "Code" tab.

Double Comments

As of March 2021, in Scratch 3.0, comments are sometimes duplicated.[citation needed] Sometimes, Scratchers will send 1 comment, and after posting the comment, see that they sent 1 comment, and leave the page.[clarify] Other Scratchers see it as 2 entirely same comments, which might be considered spam.

Automatic Logout Bug

The cookies sent by scratch:abouta
Note Warning: Visiting pages such as causes one's account to be logged out, which may lead to one's recent changes to their projects being lost.

This is most commonly experienced when visiting a page such as (notice the a, any string of text after 'about' can work, even with a slash). It is due to the website sending a malformed cookie.[2]

Thumbnail bug

Many Scratchers found out their projects' thumbnails reverted back to the default Scratch cat with a white background. This is seen in many projects and it is one of the most common bugs. This bug was reported on many topics and posts. It spread rapidly, and as of June 2021, it is still not fixed. It was first seen in May 2021. A simulation of this bug may be made within the animated project thumbnail set.[3][4] The exact cause is unknown but it could be because Scratch is unable to load the image.

Invalid Characters Bug

Main article: Undefined Hat Block
The empty Hat block.

Putting a control character (such the "NAK" character, and other characters) into the text box of a custom block results in an empty undefined Hat block. The newly created custom block will not show up in the Block Palette. The method can be found in the undefined blocks article.

More of the example tricks used with the NAK (shift in) characters are:

  • No text costumes and sounds
  • Variables remaining even if removed
  • Variables showing "i" and "j"
The variable was removed but remains there in the stage.
No text sound normally won't happen. Though this can also be made by the ZWJ (Zero-width-joiner) and ZWNJ (Zero-width-non-joiner).
The costume editor also glitches.
The stack blocks disappeared.

Backdrop and costumes bug

By uploading a GIF for the backdrop, the frames will be ordered wrong. That glitch also occurs for sprites inside the Paint Editor, but will not outside of it uploading by adding a sprite. Though backdrop uploading a GIF will also be ordered wrong even outside of the Paint Editor.

Half Blocks

Putting no name in a block, or putting an ASCII character into a custom block and then removing it after creation will create a "Half block"[5] (it looks like half of a block).

Key pressed glitch

Sometimes, the script editor will say one pressed a key, but they did not. This has not been seen many times, but cannot be considered "fixed" yet due to its appearance.

Hide and show glitch

Sometimes, pressing the stack blocks to hide and show variables the checkbox is still there saying showing/hiding.

APNG glitch

Uploading an APNG will not get frames out like GIF. But it is highly possible that it is just Scratch does not support APNG. The cause is unknown.

Question mark glitch

Some emojis or special characters put into the Instructions or Notes and Credits of a project will generate a question mark.

Pixel glitch

If one shrinks a square to smaller than 1x1 and covert into bitmap, there will be a semi-transparent pixel.

Sans Serif bug

Sans Serif will appear like Serif next to the sprites selector. However, it won't mess around with anything with the project.

Text too long bug

If one puts a string that is too long in a block, the rest of the text outside the page will be on a purple background. This might not be classified as a "bug" or "glitch".

Mailbox delay bug

Sometimes, even if the message is read, it will show as not read. This often happens while visiting 2.0-style pages such as the Forum, My Stuff etc. and sometimes when visiting 3.0 style pages too like homepage.

Upload bug

The Chrome logo disappeared.

If one uploads an animated SVG, it will show like it is animated, but not in the Stage, while it will show as animated in the sprites selector.[clarify][citation needed] SVG can also cause problems like being a question mark with a box, the SVG moving to somewhere else and other problems.

403 Forbidden bug

scratch:explorea (anything after explore) will return in 403 forbidden, not 404 error. This is caused by the Fastly configuration.[citation needed]

Blurry blocks bug

On Chromium-based browsers, the blocks on the online editor become blurry when they are running. The cause for this bug is unknown, but it's been reported since October 2021 and seems to be happening only in Chromium-based browsers.[6]

Photo of blurry scratch blocks

Inaccurate studio creation date bug

For an unknown reason, and very rarely, sometimes the "created" in the studios section of the My Stuff page will show dates that are incorrect, or show dates that do not exist.[citation needed]

An incorrect date.

Ctrl-Z bug

A bug frequently reported to take place in the paint and code editor, when pressing Ctrl-Z on Windows or Command-Z on Mac (a common "undo" shortcut), instead of the last edit to be undone, it would undo the last action done to any text box instead (i.e. the project title, sprite name, costume name, etc.). This cause of the bug is unknown, although it could potentially be due to the web browser and Scratch's undo shortcuts interfering with each other. This bug appears to happen only on Chromium-based browsers.[7][8]

Null color input bug

If one drags a reporter block inside of a color input, and then presses undo, the color input will turn into a "null input".

Fixed Bugs

Disabled Keyboard Bug

This bug, seen only in Scratch 2.0, caused Scratch to not react to key presses, which impacted projects that needed key presses to work and meant that Scratchers could not program, due to most blocks needing to have words typed in them to work correctly. This bug was only seen with Firefox. There were, at the time, no ways to fix it forever, but it had been found that clicking outside Scratch (such as address bar) fixed it temporarily.[citation needed]

Semicolon Glitch

Main article: Semicolon Glitch

The Semicolon Glitch was a bug that caused a semicolon to be displayed at the bottom left of each page. It has since been fixed, but it has been brought back a few times on April Fools' Day.

Disappearing Text Bug

Main article: Disappearing Text Bug
The bug, shown in a project.

The Disappearing Text Bug was that text in some projects would disappear. It was seen in blocks with written text inside or dropdown menus. In some cases, only some text would disappear, but sometimes, almost all the text in the project would disappear.[9] It has been fixed, and although it was reported to have appeared again in Scratch 2.0, it hasn't been seen for a few years.[10]

Variables Not Fully Hiding

In Scratch 2.0, sometimes, variables did not completely disappear from the Stage when hidden via the checkbox next to its name. The exact cause is uncertain, but it is speculated that quickly switching costumes or backdrops caused it.[citation needed]

White Text

In Scratch 2.0, in Firefox, the project website was loaded with black text appearing white. The cause was unknown, but it might have had to do with the Disabled Keyboard Bug.[citation needed]

Speech Bubbles With Empty Space at the Bottom

Sometimes, there was extra space at the bottom of a speech bubble.

ln Scratch 2.0, when changing to fullscreen, the outside of a speech bubble got amplified the correct amount, but the text appeared a bit smaller relative to the bubble. The result was that the speech bubble was a bit taller than it was supposed to be. This only happened with speech bubbles with lots of text, or large speech bubbles.

Broken Thumbnails and Profile Pictures

Main article: Broken Thumbnail and Profile Picture Bug

As of June 2021, profile pictures and featured project thumbnails stopped showing. There were numerous posts about this on the forums. The bug started due to one of Scratch's subdomains,, being down. The downtime lasted 2 days, with any users trying to access images stored in it either getting a 500 Error, or getting a Guru Mediation error[11]. After that time, the downtime stopped, however, the bug continued. After the downtime, many images were corrupted, so many images still could not load. It is suspected that Fastly being down has caused the CDN2 servers to wobble. During the downtime, many people attempting to change their profile pictures got them reset to the default Scratch Cat icon.[12]

\b bug

Including the text '\b' anywhere in the editor used to corrupt the project, disallowing the editor to save the project.[13] When downloaded and uploaded to Scratch, the project used to 'fail to load'. This was fixed on Dec 14 2022.[14]


  1. topic:301611
  2. post:5382167
  3. A project thumbnail like this project thumbnail is not the same image as the real project
  4. Chiroyce (6/11/2021). "Some project thumbnails have turned into Scratch Cat on a white background, and it still happens sometimes, unpredictably." topic:520710
  5. post:6022464
  6. medians. (22/10/2021). "So, if you're experiencing Blurry Block Glitches where the blocks in the editor are blurry, this is a Chrome/Chromium and Firefox bug." post:5806319
  9. ar-topic:21219
  10. topic:114
  11. post:5328230
  12. Chiroyce (6/11/2021). "Some people are not able to change their profile pictures, and some profile pictures have turned into the default scratch cat silhouette, which is a huge problem, and it still happens sometimes, unpredictably." topic:520710
  13. topic:354435
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