The Backstory
I'm a solo developer. No team, no funding, no fancy stack. Just a laptop, Claude Code, and a problem: every online dev tool I used was uploading my data to some server.
So I built my own. Eight of them.
What I Built
| Tool | Time |
|---|---|
| JSON Formatter + CSV export | 45 min |
| Image → Base64 encoder | 30 min |
| SQL Formatter with highlighting | 1 hour |
| Markdown → HTML preview | 2 hours |
| UUID/ULID Generator | 15 min |
| Regex Tester with captures | 40 min |
| Timestamp Converter | 20 min |
| Diff Checker (LCS algo) | 1.5 hours |
Total: ~7 hours. All client-side. Zero dependencies. Single file under 30KB.
3 Lessons
1. Don't over-engineer. React + Vite + Tailwind would've been 200KB before writing logic. Plain HTML/CSS/JS. Each tool loads < 50ms.
2. Privacy sells. The #1 feedback: "wait, nothing gets uploaded?" "Runs locally" is a stronger pitch than "10+ features."
3. Build what you search for. Every tool is something I've Googled myself. The best product ideas come from your own workflow.
Try Them
👉 https://matengtian.github.io/devtools/
Need custom scripts, bug fixes, or data analysis? DM me for rates.
Built with Claude Code. Published as part of my build-in-public journey.