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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.",[38,42,43],{},"Keep the button enabled. Validate on submit. Move focus to the first error and\ndescribe it in text.",[38,45,46],{},"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.",[38,48,49],{},"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":51,"searchDepth":52,"depth":52,"links":53},"",3,[],"2026-08-03","They remove the affordance without explaining the requirement.","md","en",{},2,"\u002Flearn\u002Fen\u002Farticles\u002F2026-08-03",{"title":33,"description":55},"learn\u002Fen\u002Farticles\u002F2026-08-03",[64],"ui-ux",[66,67],"forms","accessibility","WM62nfpNMW97kvhd-JlTOgqauLUr4OkbyY5TalAHIS0",{"older":-1,"newer":70},{"id":71,"title":72,"body":73,"date":140,"description":141,"extension":56,"lang":57,"meta":142,"minutes":52,"navigation":24,"path":143,"seo":144,"stem":145,"subjects":146,"tags":148,"__hash__":151},"articles\u002Flearn\u002Fen\u002Farticles\u002F2026-08-04.md","Jitter every TTL",{"type":35,"value":74,"toc":138},[75,78,81,84,131,134],[38,76,77],{},"A warm-up script writes ten thousand cache keys in one second, each with a\none-hour TTL.",[38,79,80],{},"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.",[38,82,83],{},"The incident happens an hour after a deploy that looked completely clean, which is\nwhat makes it hard to attribute.",[85,86,90],"pre",{"className":87,"code":88,"language":89,"meta":51,"style":51},"language-python shiki shiki-themes github-dark-dimmed github-dark-dimmed","ttl = base_ttl + random.randint(0, base_ttl \u002F\u002F 10)\n","python",[91,92,93],"code",{"__ignoreMap":51},[94,95,98,102,106,109,112,115,119,122,125,128],"span",{"class":96,"line":97},"line",1,[94,99,101],{"class":100},"sM9_K","ttl ",[94,103,105],{"class":104},"sEYkB","=",[94,107,108],{"class":100}," base_ttl ",[94,110,111],{"class":104},"+",[94,113,114],{"class":100}," random.randint(",[94,116,118],{"class":117},"sQdni","0",[94,120,121],{"class":100},", base_ttl ",[94,123,124],{"class":104},"\u002F\u002F",[94,126,127],{"class":117}," 10",[94,129,130],{"class":100},")\n",[38,132,133],{},"Ten percent of randomness spreads the expiry over six minutes instead of one\nsecond. 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