System Prompt Tool
System Prompt Length Checker
See how much of your context window your system prompt consumes.
Last updated: May 2026
Your Inputs
0 characters
Results
Character count
0
Approximate token count
0
4 chars/token heuristic
% of context window
0.0%
of 128,000 token window
Tokens at 80% threshold
102,400
409,600 chars
Disclaimer:All cost estimates are approximate and based on public API pricing. Actual costs depend on your contract rate, usage patterns, and provider pricing changes. This tool does not constitute financial, legal, tax, or operational advice. Verify pricing with your AI provider's official pricing page.
Assumptions & Limitations
- 4 chars/token approximation; actual tokenizers vary.
- Does not account for formatting overhead or special tokens.
- "80% threshold" is a practical guideline, not a hard limit.