I built a free social media character limit simulator as a solo dev — here's the story

#productivity #webdev #tooling #showdev

The problem that started it all

I was writing a LinkedIn post — spent 20 minutes getting the wording
right — hit publish, and watched it collapse behind "…see more" at
Exactly the wrong sentence.

I went looking for a tool that would show me the fold line visually,
before I posted. I found character counters everywhere, but nothing
that actually previewed how the post would look on each platform.

So I built one.

What PostTruncate does

PostTruncate is a free, browser-based
post preview simulator that shows you exactly where each platform
cuts your content — live, as you type.

Platform previews:

LinkedIn (fold at ~140 mobile, ~210 desktop)
X / Twitter (280 hard limit + automatic thread splitting)
Instagram (fold at ~125 + hashtag limit warnings)
Facebook (fold at ~125 mobile, ~480 desktop)
Threads (500 character limit)
TikTok (fold at ~100 characters)

Additional tools built in:

SMS segment calculator with GSM-7 vs Unicode auto-detection
Ad safe zone previews for Facebook, Instagram, TikTok, Google Ads
Google SERP preview for meta titles and descriptions
Emoji counter and invisible character detector
Reading time calculator
Byte counter
One-tap AI tone rewriting (professional, casual, friendly, concise)

Privacy first:
Everything runs client-side. No login, no account, no data ever
leaves your browser. The only external call is the optional AI
rewriting feature.

Tech behind it

Built with Astro, runs entirely in the browser. Available in 10
languages. No frameworks for the core counter — just clean vanilla
JS so it stays fast and lightweight.

Current status

Solo project, completely free, pre-revenue. Currently focused on
SEO and growing organic traffic. The tool has grown from a simple
counter into a full simulator — platform guides, ad previews,
character counter tools for YouTube, Pinterest, Reddit, Bluesky,
Discord, WhatsApp and more.

What I learned building it

Start with one problem. I started with LinkedIn fold lines.
Everything else came from user feedback and my own frustration.
Client-side is a feature. Privacy matters to people. "Your
text never leaves your browser" is genuinely meaningful, not just
a marketing line.
Multilingual from day one is hard but worth it. Supporting
10 languages early means organic traffic from non-English markets
compounds over time.
Solo doesn't mean slow. Shipping fast and iterating based
Real usage beats planning in isolation.