[BUG] Skills upload returns "Internal server error" on Claude Web and Desktop

[annavictoriaelano]

Preflight Checklist

• I have searched existing issues and this hasn't been reported yet
• This is a single bug report (please file separate reports for different bugs)
• I am using the latest version of Claude Code

What's Wrong?

Uploading a custom skill via Settings > Capabilities > Skills returns "Internal server error" immediately on both Claude Web (browser) and Claude Desktop app. The error appears before any processing occurs.

What I've Tried

1. Hard refresh (Ctrl+Shift+R)
2. Different browsers
3. Drag and drop vs. file picker
4. Both .zip and .md formats
5. Claude Desktop app and browser (claude.ai)

Environment
OS: Windows
Browser: Microsoft Edge Version 145.0.3800.58

Additional Context
Skill file structure is valid — folder containing SKILL.md with correct YAML frontmatter (name + description). Skill was generated by Claude itself.

What Should Happen?

Skill uploads successfully and appears in the Skills list.
Actual Behavior
"Internal server error" is shown immediately. Upload fails every time.

Error Messages/Logs

Steps to Reproduce

1. Go to Settings > Capabilities > Skills
2. Click "Upload skill"
3. Select a valid .zip file containing a skill folder with SKILL.md
4. Observe error

Claude Model

Sonnet (default)

Is this a regression?

Yes, this worked in a previous version

Last Working Version

No response

Claude Code Version

Version 1.1.3189 (1b7b58)

Platform

Anthropic API

Operating System

Windows

Terminal/Shell

Windows Terminal

Additional Information

[github-actions]

Found 3 possible duplicate issues:

1. [BUG] Skills on Claude ai dissapeared, stopped working, or can't be uploaded #26298
2. [BUG] Skills are not loading to Claude Cowork on Mac #26172
3. cowork skils bug #26131

This issue will be automatically closed as a duplicate in 3 days.

• If your issue is a duplicate, please close it and 👍 the existing issue instead
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🤖 Generated with Claude Code

[adamjdavidson]

Same issue. It's part of an overall problem with skills.

• All of my skills disappeared for a while in Claude's Mac desktop version.
• When using the Skill-creator Skill, it didn't actually follow the skill carefully. Just used it as guidance and created a non-working skill.
• Weird stuff: like, when creating skills, the yaml frontmatter sometimes did appear in Claude artifacts and sometimes didn't.

All in all, seems like something broken in the Claude Skills db or something.

[jhuskisson]

Adding to this after experiencing the same issue for the last few days (was this part of the "claude can no longer write to the skill directory" update in the last ~3-5 days?) -> I can have someone in my organisation upload the exact same skill file, and it works for them. Any way of interacting with skills (add, edit, delete, replace) no longer works on my account.

Via desktop, any browser, Mac app, iPad, iPhone, incognito mode -> all apps return internal server error on attempt. I can create a skill via the 'write skill instructions' option, but neither creating via Claude nor uploading manually works.

On top of this ->

• the skill i have successfully created via the 'write skill instructions' option under 'add skill' can't be deleted.
• previously i was able to edit/update skills via claude.ai just fine, and this no longer works at all either

I highly suspect that, because I cannot replicate this with any other account in my organisation, this is an account-specific error.

[Ozymandias4501]

Same issue on my end. There was a brief period where the skills were not visible in the settings (MacOS and Web), but Claude was still able to call them and see them.

Then another issue where I couldn't delete a skill. And now I get the same "Internal Error" when trying to upload one I created with Claude.

[raidhosn]

Same here when uploading a new skill. I am using windows 11 pro

[IamGittingHub]

Can confirm this is also affecting existing uploaded skills, not just new uploads.

I have 46 custom skills on my account. 26 load fine and their files are accessible during conversations. The other 20 appear to be registered (names and descriptions show up in the system), but the actual skill files never mount to the filesystem — so Claude can see they exist but can't read any of the instructions or reference files.

This seems related to the same infrastructure issue causing upload failures. The skills are "in the system" but not being served to the runtime environment.

Pro plan, claude.ai browser on Mac.

[campbell-thinkingcap]

Same issue here, could not update a skill or add a new one.

[Ozymandias4501]

I can now add skills but cannot delete or replace old ones. So progress.

[andrew-variable]

Same. Lots of issues all of a sudden with Skills on Mac.

[sisyga]

Same issue. Have a bugged skill that I cannot delete or replace. I can also not see it's contents and get the warning "try re-uploading the skill" when I try.

[jhuskisson]

It now seems to be intermittent to me -> i temporarily could add a skill, then the next one failed. I could delete one, then the next one failed. Still not 100%

[gwillen]

It's definitely not intermittent for me -- I uploaded a skill, it uploaded but then didn't work when I tried using it, and now every skill I upload after that is broken in the same way -- none of them work and none of them can be deleted ("internal server error".)

[Minervapra]

Still have the same problems as above, can't deleate, replace or add new skills. Just get the same error message "internal server error"