GitHub - mksglu/context-mode: Privacy-first. MCP is the protocol for tool access. We're the virtualization layer for context.

Source
mcpcontext-windowllm-agentsclaude-codesession-continuitycontext-optimizationai-toolsself-hosting

Summary

Context Mode is an MCP server that intercepts tool calls (Bash, Read, WebFetch, Playwright, etc.) and executes them inside sandboxed subprocesses, returning only a compact summary to the context window instead of raw output. It achieves 94–100% context reduction per call (e.g. 56 KB Playwright snapshot → 299 B), extending a typical Claude Code session from ~30 minutes to ~3 hours. A SQLite + FTS5 session tracker survives context compaction by rebuilding full working state - active tasks, edited files, user decisions - before the conversation window is wiped.

Key Insight

  • Context savings are dramatic and measured: 315 KB of raw tool output per session becomes 5.4 KB on average. Playwright snapshots: 56 KB → 299 B (99%). GitHub Issues (20): 59 KB → 1.1 KB (98%). Access logs (500 lines): 45 KB → 155 B (100%).
  • Two distinct problems solved: (1) context bloat from raw data dumped by MCP tools, (2) session amnesia after the model compacts the conversation. Both require hooks - instruction files alone (~60% compliance) are not enough.
  • Hooks are the difference between 60% and 98% savings. Without hooks, one unrouted Playwright call undoes an entire session’s savings. With hooks, every tool call is intercepted before execution.
  • Session continuity architecture: PostToolUse hook captures every file edit, git op, error, task, and user decision into SQLite. PreCompact builds a priority-tiered XML snapshot (≤2 KB). SessionStart restores working state via a “Session Guide” injected into context - the model picks up from the last user prompt without being re-briefed.
  • Platform support varies sharply: Full session continuity on Claude Code, Gemini CLI, VS Code Copilot, OpenClaw. Partial on Cursor and OpenCode. None on Codex CLI, Antigravity, Kiro.
  • Install for Claude Code is two commands: /plugin marketplace add mksglu/context-mode then /plugin install context-mode@context-mode. Hooks, routing instructions (CLAUDE.md patch), and slash commands (/ctx-stats, /ctx-doctor, /ctx-upgrade) are configured automatically.
  • Privacy-first by design: no telemetry, no cloud sync, no account. SQLite databases live locally and are deleted when session ends (unless --continue is used).
  • Security policy integration: Deny/allow rules from .claude/settings.json are enforced inside the sandbox too - commands chained with &&, ;, or | are split and each part checked.
  • FTS5 search with three-layer fallback: Porter stemming → trigram substring → Levenshtein fuzzy correction. Enables the model to retrieve specific indexed content rather than re-loading full documents.