Every web page, log file and GitHub issue Claude reads lands in its context window. Context Mode's README puts it plainly: after 30 minutes, 40% of your context is gone. Context Mode is a Claude Code plugin (over 29,000 stars on GitHub) that runs that work in a sandbox and sends back only the answer.
Here's what it does, how to install it in two lines, the catch, and a first prompt to try.
What it does
- Sandboxed tool calls: each ctx_execute call runs in its own subprocess, and only what it prints comes back into the chat. On the README's own test, 315 KB of output becomes 5.4 KB, a 98% cut.
- Real examples from the README: a 56 KB Playwright snapshot comes back as 299 bytes; 47 file reads (700 KB) become one 3.6 KB call.
- Search instead of re-reading: big output is indexed in a local SQLite search index, so Claude can look up the one part it needs later.
- Session memory: before Claude compacts the chat it saves a small snapshot (2 KB or less) and restores it afterwards, so you keep working from your last prompt.
- Hooks route Claude's tool calls through the sandbox for you, so you don't have to remember to use it.
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