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Hi,</div>
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<p style="direction: ltr; margin-top: 0px; margin-bottom: 0px;"><span style="font-family: Aptos, Arial, Helvetica, sans-serif; font-size: 12pt; color: rgb(0, 0, 0);">I have been hammering the service at bit from a build I am trying to make reproducible. I have
been hitting the endpoint for Ortholog mapping. If you see an issue from a client on the US East Coast, Maine, it may be me. I will cache the information and stop doing that forthwith 😊 I will set the User-Agent too.</span></p>
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Best,</div>
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Matt</div>
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<b>From: </b>Dev <dev-bounces@ensembl.org> on behalf of Stefano Giorgetti <sgiorgetti@ebi.ac.uk><br>
<b>Date: </b>Thursday, February 19, 2026 at 1:47 PM<br>
<b>To: </b>dev@ensembl.org <dev@ensembl.org><br>
<b>Subject: </b>[EXTERNAL]Re: [ensembl-dev] Noticing very slow requests on `rest.ensemble.org`<br>
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<p class="ms-outlook-mobile-reference-message skipProofing">Dear Kat,</p>
<p class="ms-outlook-mobile-reference-message skipProofing">Thank you for reaching out to us and for the helpful diagnostics.</p>
<p class="ms-outlook-mobile-reference-message skipProofing">You are correct in observing a change in Ensembl REST API behaviour.<br>
On 16th February we temporarily introduced additional traffic controls as part of a security investigation.<br>
This included more aggressive throttling of certain traffic patterns and user agents while we assessed and mitigated the issue.</p>
<p class="ms-outlook-mobile-reference-message skipProofing">Those measures have now been relaxed and normal service parameters have been restored.<br>
However, we are still seeing elevated levels of automated traffic, and some requests — particularly those matching common programmatic user agents — may intermittently experience increased latency while our safeguards continue to operate.</p>
<p class="ms-outlook-mobile-reference-message skipProofing">Your reported usage pattern (a few requests per minute) is entirely reasonable and should not require any changes on your side.<br>
That said, as a general best practice, we recommend:</p>
<ul data-start="971" data-end="1269">
<li>
<p class="ms-outlook-mobile-reference-message skipProofing" role="presentation">Including a descriptive User-Agent string that identifies your application (e.g.
<span style="font-family: "Courier New", Courier, monospace;"><code>YourAppName/1.0 (contact@email</code></span><span style="font-family: Helvetica, Arial, sans-serif;"><code>)</code></span> rather than the default
<span style="font-family: "Courier New", Courier, monospace;"><code>python-requests/x.y.z</code></span>).</p>
</li><li>
<p class="ms-outlook-mobile-reference-message skipProofing" role="presentation">Implementing exponential back off and retry handling for occasional transient slowdowns.</p>
</li><li>
<p class="ms-outlook-mobile-reference-message skipProofing" role="presentation">Avoiding burst patterns where possible.</p>
</li></ul>
<p class="ms-outlook-mobile-reference-message skipProofing">We are continuing to monitor traffic closely and fine-tune the controls to minimise impact on legitimate users.<br>
Please let us know if you continue to experience significant delays over the coming days, and we will be happy to investigate further.</p>
<p class="ms-outlook-mobile-reference-message skipProofing">Thank you for your patience and for using the Ensembl REST API.</p>
<p class="ms-outlook-mobile-reference-message skipProofing">Kind regards,</p>
<p class="ms-outlook-mobile-reference-message skipProofing">SG</p>
<pre><div class="moz-signature">--
------------
Stefano Giorgetti - Ensembl Platform Lead
The European Bioinformatics Institute (EMBL-EBI)
Wellcome Genome Campus
Hinxton, Cambridge
CB10 1SD, United Kingdom
<a href="https://www.ensembl.org/" class="moz-txt-link-freetext" data-outlook-id="b8eb07c9-cc3a-48e9-986e-3631a189a54c">https://www.ensembl.org/</a></div></pre>
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<div class="moz-cite-prefix">On 19/02/2026 6:33 pm, Kat Salameh wrote:</div>
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Hello,</div>
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We use the ensembl REST API to look up genome data in our application, typically at the rate of a few requests per minute at most. We've noticed recently that requests to `<a href="http://rest.ensembl.org/" target="_blank" data-outlook-id="616b7f13-c7e5-4a97-8e39-ed0bbdc5c7eb">rest.ensembl.org</a>`
have been taking an exceptionally long time. Specifically, since about 21:00 UTC on February 16, we've been seeing over half of requests to any `<a href="http://rest.ensembl.org/" target="_blank" data-outlook-id="46a12d2f-404b-4b17-b549-54fbeb0078c3">rest.ensembl.org</a>`
endpoint take more than 30 seconds. There aren't any changes to the statuses or other data returned that I can see, just that requests have suddenly begun to take an extremely long time.</div>
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I tried testing on my laptop with `curl` to see if I could reproduce the issue, and it did happen when I tried to use the same user agent string as our script/application.</div>
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For example:<br>
-The command `curl <a href="https://rest.ensembl.org/info/assembly/homo_sapiens%5C" target="_blank" data-outlook-id="c20f8c12-e161-4654-90da-48edac29062b">
https://rest.ensembl.org/info/assembly/homo_sapiens\</a> -H "Content-Type: application/json"` returns a result from the server in less than a second from my laptop, which is what I would expect.</div>
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- Using the same user agent as my laptop's Chrome browser has the same result.</div>
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- However, if I add `-A "python-requests/2.32.4"` to that curl command, mimicking the python requests user agent we use for programmatic access in our application, the same request now takes between 45-120 seconds or more.</div>
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Did anything change about the configuration of `<a href="http://rest.ensembl.org/" target="_blank" data-outlook-id="dd8889d6-3c0f-4eb4-80f2-d9df12221a15">rest.ensembl.org</a>` that might be causing requests to be delayed by 10s of seconds? Should we change
how we're requesting data from `<a href="http://rest.ensembl.org/" target="_blank" data-outlook-id="9dbee259-7e6c-4d1d-ba12-7b0403b00b0e">rest.ensembl.org</a>` to address this issue? Any guidance would be appreciated. Thank you!</div>
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Best,</div>
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Kat Salameh</div>
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Software Engineer at Benchling</div>
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