Custom Instructions Character Limit Checker

What is the Custom Instructions Character Limit Checker?

ChatGPT's custom instructions and Claude's profile/project instructions each have a character limit — but the exact number depends on which plan and which surface you're using, and not every limit is clearly documented in one place. This tool gives you a live counter against whichever limit applies to you.

An important honesty note on these numbers

ChatGPT's custom instructions limit is officially documented: 1,500 characters per field on Free/Go plans, expanded to 5,000 characters on Plus, Pro, Team and Enterprise plans as of a 2026 update. Claude's limits are less consistently documented across official sources — the profile-level instructions field is commonly reported around 1,500 characters, and Claude Projects' custom instructions are commonly cited around 8,000 characters in practice, but neither is a hard number Anthropic has published as prominently as OpenAI's. Because of that uncertainty, every limit here is a plain, editable number field — treat the presets as a starting guide, not a guarantee, and adjust the limit if you find the actual product behaves differently.

How to use it

1. Pick the closest preset, or enter a custom limit if you know your exact one.
2. Paste or type your instructions.
3. Watch the live count and bar — trim if you're over, since most of these platforms will either reject or silently truncate text past the limit.