What is a Context Window?

A context window is the maximum amount of text — measured in tokens — that an AI language model can process in a single interaction. It includes everything: your system prompt, the conversation history, any documents or data you paste in, and the model's own response. Think of it as the model's working memory. Once you exceed the context window, the model either refuses the request, silently truncates older content, or degrades in quality as important context gets pushed out. Understanding context windows is essential for designing prompts that work reliably, especially when working with long documents, multi-turn conversations, or complex instructions.

Context window sizes vary dramatically across models. GPT-4o supports 128K tokens (roughly 96,000 words or a 300-page book). Claude offers models with up to 200K tokens, and some configurations extend to 1M tokens. Gemini 1.5 Pro supports up to 2M tokens. However, bigger is not always better — models tend to perform best when the most relevant information is positioned at the beginning or end of the context (the "lost in the middle" problem). A 200K context window does not mean you should always fill it. Focused, well-structured context with only the most relevant information typically outperforms dumping everything into a massive prompt.

Strategies for working within context limits include chunking long documents and processing them in parts, using summarization to compress prior conversation history, prioritizing the most relevant sections of source material, and leveraging RAG to dynamically retrieve only what is needed. For multi-turn conversations, be aware that every message in the history consumes tokens — long chats eventually push out your original instructions. Reset or summarize periodically. Use a token calculator to measure exactly how much context you are consuming and plan your prompts accordingly.

Context Window Prompt Templates

Copy-ready prompts for managing, optimizing, and maximizing your AI context window.

Context Prioritization

You are processing a request that exceeds the available context window. Prioritize what information to include.

User's goal: {{user_goal}}
Available information sources:
{{information_sources}}

Total estimated tokens: {{total_tokens}}
Context budget: {{context_budget}} tokens

Prioritize using these rules:
1. **Critical** (always include): System instructions, current user query, and any data directly referenced in the query
2. **High** (include if space allows): Recent conversation turns (last 3-5), primary source documents
3. **Medium** (compress or summarize): Older conversation history, secondary reference material
4. **Low** (drop first): Examples that are similar to already-included ones, boilerplate, verbose formatting

Output a prioritized context plan:
- What to include verbatim (with token estimates)
- What to summarize (with target compression ratio)
- What to exclude (with justification)
- Final estimated token count
user_goalinformation_sourcestotal_tokenscontext_budget

Why it works: Explicit prioritization tiers prevent the common mistake of filling context with low-value information while critical data gets truncated. The compression ratios for medium-priority content maximize information density.

Long Document Chunking Strategy

You are preparing a long document for processing within a limited context window. Break it into optimal chunks.

Document type: {{document_type}}
Document length: {{document_length}} tokens
Context window size: {{window_size}} tokens
Processing task: {{task_description}}

Design a chunking strategy:

1. **Chunk sizing**: Calculate optimal chunk size considering:
   - Reserve tokens for: system prompt (~500), task instructions (~300), output (~{{output_tokens}})
   - Available per chunk: {{window_size}} - reserved tokens
   - Overlap between chunks: 10-15% for continuity

2. **Chunk boundaries**: Split at natural boundaries:
   - Prefer: section headers, paragraph breaks, complete sentences
   - Avoid: mid-sentence, mid-paragraph, mid-code-block

3. **Processing order**: For this task type ({{task_description}}):
   - Sequential: process chunk 1, then 2, carrying forward a running summary
   - Map-reduce: process all chunks independently, then merge results
   - Hierarchical: summarize sections, then analyze summaries

4. **Cross-chunk context**: What to carry between chunks:
   - Running summary of previous chunks (keep under 200 tokens)
   - Key entities/facts discovered so far
   - Unanswered questions to watch for

Output the chunking plan with estimated token counts per chunk.
document_typedocument_lengthwindow_sizetask_descriptionoutput_tokens

Why it works: Naive chunking breaks documents at arbitrary points and loses cross-chunk context. This strategy preserves semantic boundaries, calculates precise token budgets, and selects the right multi-pass approach for the task.

Conversation Summarization

You are a conversation memory manager. Summarize the conversation history to free up context window space while preserving essential information.

Current conversation ({{conversation_tokens}} tokens):
{{conversation_history}}

Compression target: Reduce to approximately {{target_tokens}} tokens.

Create a structured summary that preserves:

1. **Key decisions made**: What was agreed upon or decided
2. **Important facts established**: Data, numbers, names, and specifics mentioned
3. **Current task state**: What the user is working on right now
4. **User preferences expressed**: Any stated preferences, constraints, or requirements
5. **Open questions**: Anything unresolved that may come up again
6. **Critical instructions**: Any standing instructions the user gave (e.g., "always use TypeScript", "format as markdown")

Format the summary as:
---
CONVERSATION SUMMARY (turns 1-{{last_summarized_turn}}):
[Concise narrative summary]

KEY FACTS: [bullet list]
ACTIVE TASK: [one line]
STANDING INSTRUCTIONS: [bullet list]
OPEN ITEMS: [bullet list]
---

This summary will replace the full conversation history. Ensure nothing critical is lost.
conversation_tokensconversation_historytarget_tokenslast_summarized_turn

Why it works: Progressive summarization is the standard technique for long conversations. The structured format ensures standing instructions and user preferences survive compression, preventing the frustrating "I already told you that" experience.

Context Injection Template

You are an AI assistant. Your context has been structured using the following injection template. Parse and use each section according to its role.

<system_instructions>
{{system_prompt}}
</system_instructions>

<user_profile>
{{user_context}}
</user_profile>

<reference_documents>
{{documents}}
</reference_documents>

<conversation_summary>
{{prior_summary}}
</conversation_summary>

<recent_messages>
{{recent_turns}}
</recent_messages>

<current_request>
{{user_message}}
</current_request>

Processing rules:
- System instructions have highest priority — never override them
- Reference documents are factual context — cite them, don't contradict them
- Conversation summary provides background — use it for continuity but don't rehash it
- Recent messages are the immediate thread — respond to these directly
- If reference documents conflict with conversation context, prefer the documents
system_promptuser_contextdocumentsprior_summaryrecent_turnsuser_message

Why it works: XML-delimited context injection gives the model clear section boundaries, preventing instruction-data confusion. The explicit priority rules resolve conflicts between context sources, which is critical when context is assembled from multiple systems.

Memory Management for Long Sessions

You are managing your own memory across a long interaction session. Monitor context usage and take action to prevent degradation.

Current context usage: approximately {{current_usage}}% of {{max_tokens}} token window
Session turn count: {{turn_count}}

Memory management protocol:

## When usage < 50%:
- Operate normally, retain full conversation history
- No compression needed

## When usage reaches 50-75%:
- Begin noting which earlier turns are no longer relevant
- Flag to user: "We're at ~{{current_usage}}% context. I'll start summarizing older turns soon."

## When usage reaches 75-90%:
- Summarize all turns older than the last 5 into a compressed summary
- Preserve: all code snippets, file paths, decisions, and current task state
- Drop: greetings, acknowledgments, exploratory questions that were resolved

## When usage exceeds 90%:
- Aggressive compression: summarize everything except the last 3 turns
- Alert user: "Context is nearly full. Consider starting a new session or I can create a handoff summary."
- Generate a handoff document that can bootstrap a fresh session

Current state assessment:
Based on {{current_usage}}% usage at turn {{turn_count}}, recommend the appropriate action now.
current_usagemax_tokensturn_count

Why it works: Proactive memory management prevents the silent quality degradation that happens when context fills up. The tiered thresholds give appropriate responses at each stage, and the handoff document ensures continuity across sessions.

Token Budget Planner

You are a token budget planner for AI prompt engineering. Given the components of a prompt, calculate and optimize the token allocation.

Model: {{model_name}}
Total context window: {{context_window}} tokens
Max output tokens: {{max_output}} tokens

Prompt components:
{{prompt_components}}

Calculate the budget:

| Component | Estimated Tokens | % of Window | Priority |
|-----------|-----------------|-------------|----------|
| System prompt | ? | ? | Critical |
| [Each listed component] | ? | ? | ? |
| Output reservation | {{max_output}} | ? | Critical |
| Safety buffer (5%) | ? | ? | Critical |
| **Available for content** | **?** | **?** | — |

Optimization recommendations:
1. If total exceeds budget: What to cut or compress first
2. If under budget: What additional context would improve quality
3. Token-saving rewrites: Identify verbose sections that can be tightened without losing meaning
4. Model-specific tips: For {{model_name}}, where should the most important content be placed (beginning/end)?

Rule of thumb: Never allocate more than 80% of the context window to input. The remaining 20% is for output + safety margin.
model_namecontext_windowmax_outputprompt_components

Why it works: Most developers guess at token budgets and discover problems at runtime. This planner forces upfront allocation, prevents the common mistake of not reserving enough output tokens, and provides model-specific placement advice.