--- title: "Jaehyun Cho (@jonhisking) | Hashnode" description: "Tagline \n\nIndie developer from Korea · building TokenSave, a free AI token & API cost calculator in 34 languages" url: "https://hashnode.com/@jonhisking" --- @jonhisking # Jaehyun Cho @jonhisking · Seoul, South Korea · Joined September 2026 Tagline Indie developer from Korea · building TokenSave, a free AI token & API cost calculator in 34 languages ### [I built 60+ free browser tools for game devs. Here is what I learned.](https://tokensave.hashnode.dev/i-built-60-free-browser-tools-for-game-devs-here-is-what-i-learned?utm_source=hashnode&utm_medium=feed) 63 free browser tools for game devs: pixel art, hit feel, particles and 2D rigging. How to use them and what testing in Godot and Unity taught me. 4 min read · [tokensave.hashnode.dev](https://tokensave.hashnode.dev/i-built-60-free-browser-tools-for-game-devs-here-is-what-i-learned?utm_source=hashnode&utm_medium=feed) [Nov 3](https://hashnode.com/posts/i-built-60-free-browser-tools-for-game-devs-here-is-what-i-learned/6ae9d47cc3edb3255fba3c0d) ### [Claude Haiku vs Opus on 25 real bugs: 52 vs 54 clean fixes, 95% cheaper](https://tokensave.hashnode.dev/claude-haiku-vs-opus-on-25-real-bugs-52-vs-54-clean-fixes-95-cheaper?utm_source=hashnode&utm_medium=feed) Last week I measured where Claude Haiku 5.5 falls behind Opus. The answer was one hard bug in the marked parser, where Sonnet and Opus caught an edge case the bug report left out and Haiku mostly did 6 min read · [tokensave.hashnode.dev](https://tokensave.hashnode.dev/claude-haiku-vs-opus-on-25-real-bugs-52-vs-54-clean-fixes-95-cheaper?utm_source=hashnode&utm_medium=feed) [Oct 25](https://hashnode.com/posts/claude-haiku-vs-opus-on-25-real-bugs-52-vs-54-clean-fixes-95-cheaper/6add5a0bfca8b027c6393c9e) ### [What Claude Code sends before you type: 58 versions measured, from July 2025 to this week](https://tokensave.hashnode.dev/what-claude-code-sends-before-you-type-58-versions-measured-from-july-2025-to-this-week?utm_source=hashnode&utm_medium=feed) Every Claude Code request starts with the same fixed block: the system prompt and the definitions of every built-in tool. You pay for it before your own words are counted, and it is a big reason why s 5 min read · [tokensave.hashnode.dev](https://tokensave.hashnode.dev/what-claude-code-sends-before-you-type-58-versions-measured-from-july-2025-to-this-week?utm_source=hashnode&utm_medium=feed) [Oct 24](https://hashnode.com/posts/what-claude-code-sends-before-you-type-58-versions-measured-from-july-2025-to-this-week/6adca3fbe898b47fc569dbba) ### [Where Claude Haiku falls behind Opus: 163 coding runs with hidden tests](https://tokensave.hashnode.dev/where-claude-haiku-falls-behind-opus-163-coding-runs-with-hidden-tests?utm_source=hashnode&utm_medium=feed) Most "which model should I use for coding" advice is a guess. I wanted a line: the point where the cheap model (Claude Haiku 5.5) starts falling behind and you should pay for Sonnet or Opus. So I ran 8 min read · [tokensave.hashnode.dev](https://tokensave.hashnode.dev/where-claude-haiku-falls-behind-opus-163-coding-runs-with-hidden-tests?utm_source=hashnode&utm_medium=feed) [Oct 23](https://hashnode.com/posts/where-claude-haiku-falls-behind-opus-163-coding-runs-with-hidden-tests/6adb8726b900edba57c5ba72) ### [Same code, about 60% more output tokens on Claude: 80 runs across Claude Code, Codex and Antigravity in 5 languages](https://tokensave.hashnode.dev/same-code-about-60-more-output-tokens-on-claude-80-runs-across-claude-code-codex-and-antigravity-in-5-languages?utm_source=hashnode&utm_medium=feed) Update (Oct 23): Antigravity now has 5 runs per language as well, so the dataset has 100 runs. Opus in Antigravity came out at 602 output tokens per 1,000 characters (was 596), and the gap to Gemini a 5 min read · [tokensave.hashnode.dev](https://tokensave.hashnode.dev/same-code-about-60-more-output-tokens-on-claude-80-runs-across-claude-code-codex-and-antigravity-in-5-languages?utm_source=hashnode&utm_medium=feed) [Oct 23](https://hashnode.com/posts/same-code-about-60-more-output-tokens-on-claude-80-runs-across-claude-code-codex-and-antigravity-in-5-languages/6adacf4c4b8109665efcf861)