FmtDev
Language
View on GitHub

LLM Token Counter & Budget Estimator

FmtDev LLM Token Counter & Budget Estimator is a free, browser-based tool that calculate token counts and estimate costs for GPT, Claude, and Gemini. Optimize your prompts within the context window. It runs entirely on your device with zero data transmission, making it safe for proprietary code and sensitive content.

🛡️ 100% Client-Side. Your data never leaves your browser.
ADVERTISEMENT

Mastering LLM Context: A 2026 Guide to GPT-5.4 and Claude 4.6 Budgeting

Why is Token Accuracy Critical in the Reasoning Era?

With the release of GPT-5.4 Thinking and Claude 4.6 Opus in early 2026, the industry has shifted from 'simple completion' to 'extended reasoning.' Unlike 2025 models, modern agents generate hidden reasoning tokens. If you don't calculate your input-to-output ratio accurately, you risk 'Context Overflow'—where the model loses the system instructions because the RAG context is too large. Our local counter helps you maintain the perfect 80/20 balance between context and reasoning headroom.

The Cost of a 1-Million Token Context

As of March 2026, Claude 4.6 provides a massive 1M token window. While revolutionary, a full context prompt costs approximately $5.00. For production agents running hourly, this technical choice can make or break your SaaS margins. By using FmtDev's 100% local tokenizer, you can audit your prompt cost across GPT-5.4, Claude, and Gemini without transmitting proprietary data to any third-party backend server.

ADVERTISEMENT
How to use

How to use LLM Token Counter

  1. 1

    Paste your system or user prompt in the input area.

  2. 2

    Select the target LLM model to use its specific tokenizer.

  3. 3

    Set your expected output reserve to see the remaining budget.

  4. 4

    Check the total token count and estimated cost instantly.

FAQ

Which tokenizers do you use?
We use the official tok-p for GPT and specific mappings for Claude and Gemini, running 100% locally.
Is the cost estimation accurate?
It uses the latest March 2026 pricing, but always check your provider dashboard for billing.

Mastering LLM Context: A 2026 Guide to GPT-5.4 and Claude 4.6 Budgeting

Why is Token Accuracy Critical in the Reasoning Era?

With the release of GPT-5.4 Thinking and Claude 4.6 Opus in early 2026, the industry has shifted from 'simple completion' to 'extended reasoning.' Unlike 2025 models, modern agents generate hidden reasoning tokens. If you don't calculate your input-to-output ratio accurately, you risk 'Context Overflow'—where the model loses the system instructions because the RAG context is too large. Our local counter helps you maintain the perfect 80/20 balance between context and reasoning headroom.

The Cost of a 1-Million Token Context

As of March 2026, Claude 4.6 provides a massive 1M token window. While revolutionary, a full context prompt costs approximately $5.00. For production agents running hourly, this technical choice can make or break your SaaS margins. By using FmtDev's 100% local tokenizer, you can audit your prompt cost across GPT-5.4, Claude, and Gemini without transmitting proprietary data to any third-party backend server.