Koray Güler builds product at koative, an independent software studio in İstanbul. Notes on typed edges, small dependency lists and calm software.https://koray.dev/https://koray.dev/posts/llm-cannot-hallucinate-what-you-never-sent/https://koray.dev/posts/llm-cannot-hallucinate-what-you-never-sent/Anti-hallucination gets written as a prompt rule. It belongs in the code that builds the prompt, and the sharpest version of it is one line long.Sat, 18 Jul 2026 06:00:00 GMThttps://koray.dev/posts/the-label-was-not-the-identity/https://koray.dev/posts/the-label-was-not-the-identity/A rendering layer derives a human label from a machine identity. Both are strings. The type checker has nothing to say and the money path does.Sat, 04 Jul 2026 06:00:00 GMThttps://koray.dev/posts/cache-the-prompt-not-the-inputs/https://koray.dev/posts/cache-the-prompt-not-the-inputs/The key listed the inputs someone believed mattered. The prompt had grown three fields since, and nothing in the system could have noticed.Sat, 27 Jun 2026 06:00:00 GMThttps://koray.dev/posts/the-endpoint-that-succeeded-at-doing-nothing/https://koray.dev/posts/the-endpoint-that-succeeded-at-doing-nothing/Correct status code, clean logs, zero exceptions, wrong data. What happens to the promise you deliberately didn't await.Fri, 05 Jun 2026 06:00:00 GMThttps://koray.dev/posts/a-signing-key-in-the-browser/https://koray.dev/posts/a-signing-key-in-the-browser/What that buys, split by what the attacker can already do, and why the property that actually protects the user is not in my code at all.Sat, 30 May 2026 06:00:00 GMThttps://koray.dev/posts/the-page-cache-we-deleted/https://koray.dev/posts/the-page-cache-we-deleted/Three rounds of tuning to cut the write bill, then removal. The same machinery stayed for images.Thu, 14 May 2026 06:00:00 GMThttps://koray.dev/posts/your-error-handler-is-inside-the-cache/https://koray.dev/posts/your-error-handler-is-inside-the-cache/A container restart took thirty seconds. The site stayed broken for an hour after it came back.Thu, 23 Apr 2026 06:00:00 GMThttps://koray.dev/posts/a-missing-capability-beats-a-threshold/https://koray.dev/posts/a-missing-capability-beats-a-threshold/A limit can be misconfigured, and mine throttled the one thing that was supposed to recover from the problem it was throttling.Sat, 04 Apr 2026 06:00:00 GMThttps://koray.dev/posts/idempotent-writes-idempotent-side-effects/https://koray.dev/posts/idempotent-writes-idempotent-side-effects/The upsert was the easy half. The write also caused four other things, and none of them were idempotent for free.Thu, 19 Mar 2026 06:00:00 GMThttps://koray.dev/posts/math-floor-is-not-a-floor/https://koray.dev/posts/math-floor-is-not-a-floor/The obvious fix drops a step. The clever fix rounds past the input. Neither raises an exception, and only one of them spends money you don't have.Thu, 26 Feb 2026 06:00:00 GMT