SageMath output blocked by CORS policy

[Thomas Shemanske]

Hopefully I am not asking a silly question, but I​ was testing some old PreTeXt docs with sage cells and noticed they were not rendering output.  So as a check I went to the PTX guide https://pretextbook.org/doc/guide/html/basics-s-sage-cell.html​, and tried to evaluate that cell; it too produced no output.

The developer error logs for Chrome and Firefox are below in full, but the gist is:

basics-s-sage-cell.html:1 Access to XMLHttpRequest at 'https://sagecell.sagemath.org/kernel?CellSessionID=9377c8c…&timeout=inf&accepted_tos=true' from origin 'https://pretextbook.org' has been blocked by CORS policy: Response to preflight request doesn't pass access control check: No 'Access-Control-Allow-Origin' header is present on the requested resource.

​Since I have viewed sage cells many times on these browsers, and my local copy of Sage works fine, I am not thinking it is a browser issue, but who knows.

Since I was not using one of my documents, pretext support may not be useful, but here is a short version:

pretext support
PreTeXt-CLI version: 2.36.0

warning: No project.ptx manifest found in current workspace.  Using global configuration specified in '~/.ptx/2.36.0/project.ptx'.

Please share the following information when posting to the
pretext-support Google Group.

PreTeXt-CLI version: 2.36.0
   PyPI link: https://pypi.org/project/pretextbook/2.36.0/
PreTeXt core resources commit: 3b7177a830a26fbb7595a2edeaf09478ca71ac93
OS: Linux-6.18.5+deb14-amd64-x86_64-with-glibc2.42
Python version: 3.13.11, running from /home/trs/.local/share/pipx/venvs/pretext/bin/python
Current working directory: /home/trs
No project.ptx found.

Any guidance appreciated.

Tom

Chrome error log:

tex-chtml.js:1 No version information available for component [tex]/newcommand
console.js:19 sagecell.makeSagecell called
console.js:19 sagecell.makeSagecell finished
basics-s-sage-cell.html:1331 A parser-blocking, cross site (i.e. different eTLD+1) script, https://secure.statcounter.com/counter/counter.js, is invoked via document.write. The network request for this script MAY be blocked by the browser in this or a future page load due to poor network connectivity. If blocked in this page load, it will be confirmed in a subsequent console message. See https://www.chromestatus.com/feature/5718547946799104 for more details.
basics-s-sage-cell.html:1331 A parser-blocking, cross site (i.e. different eTLD+1) script, https://secure.statcounter.com/counter/counter.js, is invoked via document.write. The network request for this script MAY be blocked by the browser in this or a future page load due to poor network connectivity. If blocked in this page load, it will be confirmed in a subsequent console message. See https://www.chromestatus.com/feature/5718547946799104 for more details.
tex-chtml.js:1 No version information available for component [pretext]/mathjaxknowl3.js
basics-s-sage-cell.html:90 in ready function
bookfuncs.js:504 This page served by undefined
bookfuncs.js:592 triggering runestone:pre-login-complete
webpack.index.js:208 Runestone pre-login complete
pretext_add_on.js?x=1:192 adding video popouts
pretext_add_on.js?x=1:305 scrollWidth 15
pretext.js:50 setting up pretext
/favicon.ico:1 Failed to load resource: the server responded with a status of 404 (Not Found)
runestonebase.js:146 Not logging event {"event":"sage","act":"run","div_id":"basics-s-sage-cell-8","course_name":"PTX_Course_Title_Here","clientLoginStatus":false,"timezoneoffset":5}
basics-s-sage-cell.html:1 Access to XMLHttpRequest at 'https://sagecell.sagemath.org/tos.html' from origin 'https://pretextbook.org' has been blocked by CORS policy: No 'Access-Control-Allow-Origin' header is present on the requested resource.
kernel.js:107 Kernel: kernel_starting (null)
sagecell.sagemath.org/tos.html:1 Failed to load resource: net::ERR_FAILED
​basics-s-sage-cell.html:1 Access to XMLHttpRequest at 'https://sagecell.sagemath.org/kernel?CellSessionID=9377c8c…&timeout=inf&accepted_tos=true' from origin 'https://pretextbook.org' has been blocked by CORS policy: Response to preflight request doesn't pass access control check: No 'Access-Control-Allow-Origin' header is present on the requested resource.
utils.js:731

Object

utils.js:733 API request failed (0): error
sagecell.sagemath.or…accepted_tos=true:1 Failed to load resource: net::ERR_FAILED

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Firefox​ error log:

Cookie warnings 3
No version information available for component [tex]/newcommand tex-chtml.js:1:16471
Layout was forced before the page was fully loaded. If stylesheets are not yet loaded this may cause a flash of unstyled content. jquery.min.js:2:50785
sagecell.makeSagecell called console.js:19:25
sagecell.makeSagecell finished console.js:19:25
No version information available for component [pretext]/mathjaxknowl3.js tex-chtml.js:1:16471
GEThttps://pretextbook.org/favicon.ico[HTTP/1.1 404 Not Found 42ms]
in ready function basics-s-sage-cell.html:90:15
This page served by undefined bookfuncs.js:504:13
triggering runestone:pre-login-complete bookfuncs.js:592:13
Runestone pre-login complete webpack.index.js:208:13
adding video popouts pretext_add_on.js:192:13
scrollWidth 0 pretext_add_on.js:305:14
setting up pretext pretext.js:50:13
Partitioned cookie or storage access was provided to “https://c.statcounter.com/t.php?sc_project=9664088&u1=F63635D6C5F94FC996E8CB33758FE19C&java=1&security=6e60c510&sc_snum=1&sess=ce99ee&p=0&rcat=d&rdomo=d&rdomg=207&jg=207&rr=3.3.2.1.1.1.1.1.1&sc_bot=0&resolution=2560&h=1440&camefrom=https%3A//pretextbook.org/doc/guide/html/part-author.html&u=https%3A//pretextbook.org/doc/guide/html/basics-s-sage-cell.html&t=SageMathCells&invisible=1&sc_rum_e_s=829&sc_rum_e_e=1640&sc_rum_f_s=0&sc_rum_f_e=813” because it is loaded in the third-party context and dynamic state partitioning is enabled.
Not logging event {"event":"sage","act":"run","div_id":"basics-s-sage-cell-8","course_name":"PTX_Course_Title_Here","clientLoginStatus":false,"timezoneoffset":5} runestonebase.js:146:21
​XHRPOSThttps://sagecell.sagemath.org/tos.htmlCORS Missing Allow Origin
Cross-Origin Request Blocked: The Same Origin Policy disallows reading the remote resource at https://sagecell.sagemath.org/tos.html. (Reason: CORS header ‘Access-Control-Allow-Origin’ missing). Status code: 503.
starting timer from 1770230949299 console.js:25:26
Kernel: kernel_starting (null) kernel.js:107:21
XHROPTIONShttps://sagecell.sagemath.org/kernel?CellSessionID=9e78482ca0fa45158468930e1099b7d4&timeout=inf&accepted_tos=trueCORS Missing Allow Origin
Cross-Origin Request Blocked: The Same Origin Policy disallows reading the remote resource at https://sagecell.sagemath.org/kernel?CellSessionID=9e78482ca0fa45158468930e1099b7d4&timeout=inf&accepted_tos=true. (Reason: CORS header ‘Access-Control-Allow-Origin’ missing). Status code: 503.
Cross-Origin Request Blocked: The Same Origin Policy disallows reading the remote resource at https://sagecell.sagemath.org/kernel?CellSessionID=9e78482ca0fa45158468930e1099b7d4&timeout=inf&accepted_tos=true. (Reason: CORS request did not succeed). Status code: (null).
Object { readyState: 0, getResponseHeader: getResponseHeader(e), getAllResponseHeaders: getAllResponseHeaders(), setRequestHeader: setRequestHeader(e, t), overrideMimeType: overrideMimeType(e), statusCode: statusCode(e), abort: abort(e), state: state(), always: always(), catch: catch(e), … }
utils.js:731:17
API request failed (0): error utils.js:733:17

Iterate on your code faster with the new multi-line editor mode. Use Enter to add new lines and Ctrl+Enter to run.

[Mitch Keller]

It appears that the SageCell server is down, as going to https://sagecell.sagemath.org/ gives me a 503 error. Thus, I’m not sure that the CORS policy message is actually an issue or if it’s a bigger issue with Sage things at the moment.

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Mitch Keller
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http://www.rellek.net/

[Randall Pruim]

The Sage folks are aware.  I alerted them this morning...

https://groups.google.com/g/sage-cell/c/EFrOEFaWlRQ/m/mLnl0SMDBwAJ?utm_medium=email&utm_source=footer&pli=1

To view this discussion visit https://groups.google.com/d/msgid/pretext-support/44D488D5-DB06-40B6-BC60-A0463360197B%40rellek.net.

[kcri...@gmail.com]

For what it's worth, it seems that the server is back up!

[Randall Pruim]

Great. Thanks for alerting me. 

Sent from my iPhone

On Feb 5, 2026, at 12:27, kcri...@gmail.com <kcri...@gmail.com> wrote:

For what it's worth, it seems that the server is back up!

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[Robert D. Poodiack]

Yep! Was able to work with it this morning in class. Thanks!

— RP 

Robert D. Poodiack, Ph.D. (he/him/his)
Professor of Mathematics

Cabot Science 288 (U288)
Norwich University
158 Harmon Drive
Northfield, VT  05663
(802) 485-2339
rpoo...@norwich.edu

  

From: pretext...@googlegroups.com <pretext...@googlegroups.com> on behalf of kcri...@gmail.com <kcri...@gmail.com>
Date: Thursday, February 5, 2026 at 12:27 PM
To: PreTeXt support <pretext...@googlegroups.com>
Subject: Re: [pretext-support] SageMath output blocked by CORS policy

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For what it's worth, it seems that the server is back up!

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