What Is a Context Window? Three Mistakes That Make You Lose Track of Your Build

A coding session can go sideways when an assistant forgets a decision you made earlier and confidently suggests the opposite approach. That failure makes more sense once you know what a context window is. It is the limited amount of information an AI model can consider while producing a response. Your instructions, conversation, pasted code, and tool results can all compete for that space.

The exact limit depends on the model and tool. When a conversation grows long, earlier material may no longer be available in full, or a tool may summarize it. You can keep moving quickly without treating the chat as a complete record of your project.

Mistake 1: Assuming the assistant can see an earlier decision

You tell an assistant in Cursor that the first version of your SaaS will use manual approvals. Later, you ask it to build the invite flow without restating that choice. If the earlier discussion is outside its available context, it may generate an automatic approval path that looks plausible but violates your plan.

Before a substantial request, give the assistant the decisions that constrain the work. A short note such as “Invites require manual approval; do not add automatic acceptance” is more useful than asking it to remember a long conversation. Keep that decision somewhere you can check after the session, especially if it affects permissions or data access.

Mistake 2: Pasting more code instead of narrowing the problem

A failed build tempts you to paste the whole repository into ChatGPT. Large inputs can crowd out the error, the relevant files, and the instructions you want followed. Even when everything fits, the assistant has more unrelated material to sort through and may propose changes outside the broken flow.

Start with the observed behavior, the expected behavior, the error, and the smallest relevant code path. Ask which additional file would help before sharing it. Review the resulting diff and run the failing test again rather than accepting a fix because its explanation sounds convincing.

Mistake 3: Leaving the working fix inside the conversation

Suppose a prompt finally helps you fix an account settings bug. The next time a similar bug appears, you remember the breakthrough but cannot find the prompt or recall which change actually worked. The context window explains the assistant's limits; scattered chat history creates a separate limit on your own ability to resume.

After a useful session, write a brief recovery note. Record the bug, the change you kept, any test you ran, and the next action. Save a reusable prompt only if you can say what result it produced. A prompt without that outcome can send a later build session down the wrong path.

Keep the project state outside the chat

A context window is useful working space, not durable project memory. At the end of your next session, leave yourself a few lines covering the current state, the decision behind it, and the first thing to check when you return. That gives you a reliable starting point even when you switch tools or open a fresh conversation.

For a complete routine from defining a task to verifying the result and leaving a recovery note, follow this step-by-step context engineering workflow.

Keep your build decisions and useful prompts in VibeCrumbs so the next session starts from the work you chose to keep.