This guide is so small it can fit into one section apparently
1. Deal with it
Just upload your screenshot with any caption — we'll edit it later, I haven't found a way of changing caption length within Steam Client's GUI.

2. Use your browser
Please log into your Steam account from your Web Browser of choice, but one that supports developing/debugging tools (Google Chrome/Chromium, Microsoft Edge will all do).

3. Open your screenshot page
Locate your Steam profile, click on Screenshots on the right side, find the screenshot you just posted (with an incomplete caption) and click "View comments & details" on the right. This will bring you to the page where you can edit the caption of your screenshot. Click "Edit caption" on the right.

4. Edit the caption field, and then edit the caption
The caption field is a normal Hyper Text Markup Language (HTML) field, and its limit is set to 140 characters maximum.
A little bit of trivia: To display the page, your browser has to download it first (it downloads every page you're viewing, you don't need to download anything on your own), so everything you see is actually stored locally, even though only temporarily.

Right now the only thing stopping you from getting a longer caption is that local value. So let's edit it!

4.1. Right-click the caption field, choose "Inspect"
4.2. On the highlighted line, search for "maxlength" attribute. It should look like this:
4.3. Obviously you want to change that 140 (double-click it) to at least something like 255, maybe more if you are very talkative today. :D
4.4. Press Enter to save what you edited, then close Developer tools.

Now you can finally write a longer caption, nice! Just click Save when you are done editing.


It is actually quite weird that the database itself even accepts captions longer than 140… Why the 140 character limit in the GUI then?