July 7, 2026Johan Huynh5 min read

Claude Code "prompt is too long": what causes it and how to fix it

The error looks like a wall. It is actually a full container. Once you see what is filling it, the fix takes about ten seconds.

The kitstarter robot beside a warning triangle, standing in for the prompt too long error

You are mid-task, you send a normal message, and Claude Code answers with Prompt is too long. Sometimes it then breaks every following input until you deal with it. It is not a bug in your prompt. Your context window, the amount of text the model can hold at once, is full, and one more message pushed it over.

What "prompt is too long" actually means

There are two different limits people mix up. Usage limit is about how much you can run over a time window, your plan's budget. Prompt is too long is about size right now: a single input exceeded the context window. This post is about the second one. It means the conversation plus whatever you just added no longer fits, so the fix is always the same shape, take stuff out of the window.

What is filling your context

Three culprits, in rough order of how often they are the real cause:

Unused MCP serversevery connected server loads tool definitions into the window, running or not
Large filesa big file pasted or pulled in whole can fill the window in one shot
A long conversationhours of back-and-forth quietly accumulate until there is no room left
The window is a fixed size. These three are what usually eat it.

The fix, in order

  1. Run /compact. It summarizes the conversation down to the essentials and lets you keep going. This is the first thing to try, it clears room without losing your thread.
  2. Or run /clear. This wipes the conversation entirely while keeping your project and CLAUDE.md loaded. Use it between unrelated tasks. Fresh window, same project.
  3. Turn off MCP servers you are not using. Each one costs window space just by being connected. Trim to the ones this task actually needs.
  4. Stop feeding it huge files. Do not paste a giant file or run /context on your whole repo. Point at what you need with @path/to/file, or split the file.
  5. Break the task down. If one request genuinely needs more than the window holds, it is too big. Do it in smaller steps.

How to stop it happening again

The people who never see this error are not lucky. They keep their context lean on purpose: /clear between unrelated tasks, /compact before a big new one, only the MCP servers they need, files referenced instead of pasted. The bonus is that a lean context is not just error-free, it is faster and cheaper, because you are not paying to reprocess a bloated window on every turn.

That habit, keep the context small and deliberate, is one of the behaviors kitstarter builds in. The kit's commands checkpoint and reset your work in clean steps so the window never quietly fills to the point of breaking, and a lean CLAUDE.md keeps the baseline small. Context bloat is not just an error message. It is the same thing that makes a long session slow and forgetful.

Common questions

Is "prompt too long" the same as hitting my usage limit? No. Usage limit is your time-based budget. Prompt too long is a single message exceeding the context window right now.

Fastest fix? /compact to summarize and continue, or /clear to reset the window while keeping your project loaded.

Why does it break every message after? Once the window is over the limit, each new input is still over it. Compact or clear to get back under.

Keep the context lean by default

kitstarter builds the habits that stop context bloat before it breaks, for Claude Code, Codex, and Antigravity.

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