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HomeToolsAI Context Window Calculator

Developer utility

• Updated Feb 22, 2026

AI Context Window Calculator

Check if your prompt fits GPT-4, Claude, Gemini context windows. Estimate tokens, usage %, and API costs per model.

Key Takeaway (AI Summary)

The AI Context Window Calculator is a zero-knowledge, browser-native utility that check if your prompt fits gpt-4, claude, gemini context windows. estimate tokens, usage %, and api costs per model with 100% privacy guarantee.

Client-side only
No signup
Instant outputPrivate by designZero tracking
0 characters~0 tokens estimated

Context Window Usage

0
Input Tokens
128.0K
Remaining
16.4K
Max Output
Yes
Fits Output?
Estimated Cost
Input: $0.0000Max Output: $0.2458Total: $0.2458

Model Comparison

ModelContextMax OutYour UsageFits?
GPT-4o128.0K16.4K0.0%—
GPT-4o mini128.0K16.4K0.0%—
GPT-4 Turbo128.0K4.1K0.0%—
GPT-3.5 Turbo16.4K4.1K0.0%—
Claude 3.5 Sonnet200.0K8.2K0.0%—
Claude 3 Opus200.0K4.1K0.0%—
Claude 3 Haiku200.0K4.1K0.0%—
Gemini 1.5 Pro2.1M8.2K0.0%—
Gemini 1.5 Flash1.0M8.2K0.0%—
Llama 3.1 405B128.0K4.1K0.0%—
Llama 3.1 70B128.0K4.1K0.0%—
Mistral Large128.0K4.1K0.0%—
DeepSeek V3128.0K8.2K0.0%—
Cohere Command R+128.0K4.1K0.0%—

Token estimates are approximate (~4 chars/token for English, ~3.2 for code). For exact counts, use the official tokenizer for your model.

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AI Context Window Calculator — Mastering Prompt Engineering Limits

As Large Language Models evolve, context windows have expanded from 8k to over 1 million tokens. However, "Attention Decay" remains a critical architectural challenge. The **DevUtility Hub AI Context Window Calculator** is a professional-grade modeling tool that helps developers visualize how their prompts occupy the limited "active memory" of flagship models like GPT-4o, Claude 3.5, and Gemini 1.5.

🧠 Navigating the Attention Bottleneck

Even if a model *can* accept 1 million tokens, its reasoning performance often degrades as a prompt nears its limit. Our calculator provides:

- **Saturation Visualization**: See a heat-map style progress bar showing exactly what percentage of the context window your input consumes.

- **Model-Specific Defaults**: Instantly toggle between 128k (GPT-4o), 200k (Claude 3.5), and 1M+ (Gemini Pro) presets to ensure your RAG pipelines are within operational bounds.

- **Cost-to-Performance Ratio**: Calculate the "Unit Economics" of your prompt. Is it worth sending a 50k token context to GPT-4o, or should you use a cheaper "mini" model for that specific payload?

- **Token Overhead Estimation**: Automatically accounts for system message overhead and estimated response length to give you a "Full Round Trip" budget.

⚡ AI Architecture Workflow

1. **Payload Ingestion**: Paste your system prompt, user instructions, and external context (like document snippets or codebases).

2. **Select Target Model**: Choose from our frequently updated list of the industry's most popular LLMs.

3. **Analyze & Refactor**: If your prompt is nearing the 80% saturation point (where attention loss often begins), use our data size converter to identify files that can be trimmed.

4. **Deploy with Confidence**: Use the final token count to set accurate max_tokens parameters in your API calls.

🛡️ Secure Prompt Modeling

Your AI architecture and system prompts are high-value IP. Sending them to a third-party calculator is a major security risk. **DevUtility Hub operates locally**. Your prompts are processed via client-side BPE heuristics, ensuring that your secret instructions and confidential data never leave your professional sandbox.

Engineer smarter, cheaper, and more reliable AI agents with the web's most precise context calculator.

Zero-Knowledge Execution & Edge Architecture

Unlike traditional monolithic developer utilities, DevUtility Hub operates entirely on a Zero-Knowledge architectural framework. When utilizing the AI Context Window Calculator, all computational workload is completely shifted to your local execution environment via WebAssembly (Wasm) and your browser's native JavaScript engine (such as V8 or SpiderMonkey).

Why Local Workloads Matter

Transmitting proprietary JSON objects, sensitive source code, or unencrypted text strings to an unknown third-party server introduces critical security vulnerabilities. By executing the AI Context Window Calculator securely within the isolated sandbox of your Document Object Model (DOM), we structurally guarantee strict compliance with major data protection regulations like GDPR, CCPA, and HIPAA. We do not ingest, log, or telemetry your text payloads. Your local RAM serves as the absolute boundary.

Network-Free Performance

Furthermore, by completely eliminating asynchronous HTTP POST payloads to a centralized cloud infrastructure, we guarantee effectively zero latency. The AI Context Window Calculator provides instant execution without arbitrary rate limits, artificial file size constraints, or server timeouts. Our global edge network serves the application wrapper, while your local machine handles the heavy lifting.

N
Nick Osta

Senior DevTools Architect • 15+ Yeaers Exp.

Subject Matter Expert Reviewed

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