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It is also skipped by keyboard focus and often unreadable against its\nbackground, so a screen reader user gets no signal at all.",[36,40,41],{},"Keep the button enabled. Validate on submit. Move focus to the first error and\ndescribe it in text.",[36,43,44],{},"The user learns what the form wants by asking, which is the interaction they were\nalready attempting. The disabled state asks them to guess instead.",[36,46,47],{},"If the action is genuinely unavailable — a plan limit, a missing permission — say so\nin text next to the control. The reason is the useful part; the disabled state is\njust the absence of one.",{"title":49,"searchDepth":50,"depth":50,"links":51},"",3,[],"2026-08-03","They remove the affordance without explaining the requirement.","md","en",{},2,"\u002Flearn\u002Fen\u002Farticles\u002F2026-08-03",{"title":31,"description":53},"learn\u002Fen\u002Farticles\u002F2026-08-03",[62],"ui-ux",[64,65],"forms","accessibility","WM62nfpNMW97kvhd-JlTOgqauLUr4OkbyY5TalAHIS0",{"older":-1,"newer":68},{"id":69,"title":70,"body":71,"date":138,"description":139,"extension":54,"lang":55,"meta":140,"minutes":50,"navigation":24,"path":141,"seo":142,"stem":143,"subjects":144,"tags":146,"__hash__":149},"articles\u002Flearn\u002Fen\u002Farticles\u002F2026-08-04.md","Jitter every TTL",{"type":33,"value":72,"toc":136},[73,76,79,82,129,132],[36,74,75],{},"A warm-up script writes ten thousand cache keys in one second, each with a\none-hour TTL.",[36,77,78],{},"One hour later, all ten thousand expire in the same second. Every request misses.\nThe database, sized for cached traffic, takes the full uncached load at once.",[36,80,81],{},"The incident happens an hour after a deploy that looked completely clean, which is\nwhat makes it hard to attribute.",[83,84,88],"pre",{"className":85,"code":86,"language":87,"meta":49,"style":49},"language-python shiki shiki-themes github-dark-dimmed github-dark-dimmed","ttl = base_ttl + random.randint(0, base_ttl \u002F\u002F 10)\n","python",[89,90,91],"code",{"__ignoreMap":49},[92,93,96,100,104,107,110,113,117,120,123,126],"span",{"class":94,"line":95},"line",1,[92,97,99],{"class":98},"sM9_K","ttl ",[92,101,103],{"class":102},"sEYkB","=",[92,105,106],{"class":98}," base_ttl ",[92,108,109],{"class":102},"+",[92,111,112],{"class":98}," random.randint(",[92,114,116],{"class":115},"sQdni","0",[92,118,119],{"class":98},", base_ttl ",[92,121,122],{"class":102},"\u002F\u002F",[92,124,125],{"class":115}," 10",[92,127,128],{"class":98},")\n",[36,130,131],{},"Ten percent of randomness spreads the expiry over six minutes instead of one\nsecond. 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