Context Compactor

Automatic context compaction for OpenClaw when using local models that don't properly report token limits or context overflow errors.

The Problem

Cloud APIs (Anthropic, OpenAI) report context overflow errors, allowing OpenClaw's built-in compaction to trigger. Local models (MLX, llama.cpp, Ollama) often:

Silently truncate context
Return garbage when context is exceeded
Don't report accurate token counts

This leaves you with broken conversations when context gets too long.

The Solution

Context Compactor estimates tokens client-side and proactively summarizes older messages before hitting the model's limit.

How It Works

┌─────────────────────────────────────────────────────────────┐
│  1. Message arrives                                         │
│  2. before_agent_start hook fires                           │
│  3. Plugin estimates total context tokens                   │
│  4. If over maxTokens:                                      │
│     a. Split into "old" and "recent" messages              │
│     b. Summarize old messages (LLM or fallback)            │
│     c. Inject summary as compacted context                 │
│  5. Agent sees: summary + recent + new message             │
└─────────────────────────────────────────────────────────────┘

Installation

# One command setup (recommended)
npx jasper-context-compactor setup

# Restart gateway
openclaw gateway restart

The setup command automatically:

Copies plugin files to ~/.openclaw/extensions/context-compactor/
Adds plugin config to openclaw.json with sensible defaults

Configuration

Add to openclaw.json:

{
  "plugins": {
    "entries": {
      "context-compactor": {
        "enabled": true,
        "config": {
          "maxTokens": 8000,
          "keepRecentTokens": 2000,
          "summaryMaxTokens": 1000,
          "charsPerToken": 4
        }
      }
    }
  }
}

Options

Option	Default	Description
`enabled`	`true`	Enable/disable the plugin
`maxTokens`	`8000`	Max context tokens before compaction
`keepRecentTokens`	`2000`	Tokens to preserve from recent messages
`summaryMaxTokens`	`1000`	Max tokens for the summary
`charsPerToken`	`4`	Token estimation ratio
`summaryModel`	(session model)	Model to use for summarization

Tuning for Your Model

MLX (8K context models):

{
  "maxTokens": 6000,
  "keepRecentTokens": 1500,
  "charsPerToken": 4
}

Larger context (32K models):

{
  "maxTokens": 28000,
  "keepRecentTokens": 4000,
  "charsPerToken": 4
}

Small context (4K models):

{
  "maxTokens": 3000,
  "keepRecentTokens": 800,
  "charsPerToken": 4
}

Commands

`/compact-now`

Force clear the summary cache and trigger fresh compaction on next message.

/compact-now

`/context-stats`

Show current context token usage and whether compaction would trigger.

/context-stats

Output:

📊 Context Stats

Messages: 47 total
- User: 23
- Assistant: 24
- System: 0

Estimated Tokens: ~6,234
Limit: 8,000
Usage: 77.9%

✅ Within limits

How Summarization Works

When compaction triggers:

Split messages into "old" (to summarize) and "recent" (to keep)
Generate summary using the session model (or configured summaryModel)
Cache the summary to avoid regenerating for the same content
Inject context with the summary prepended

If the LLM runtime isn't available (e.g., during startup), a fallback truncation-based summary is used.

Differences from Built-in Compaction

Feature	Built-in	Context Compactor
Trigger	Model reports overflow	Token estimate threshold
Works with local models	❌ (need overflow error)	✅
Persists to transcript	✅	❌ (session-only)
Summarization	Pi runtime	Plugin LLM call

Context Compactor is complementary — it catches cases before they hit the model's hard limit.

Troubleshooting

Summary quality is poor:

Try a better summaryModel
Increase summaryMaxTokens
The fallback truncation is used if LLM runtime isn't available

Compaction triggers too often:

Increase maxTokens
Decrease keepRecentTokens (keeps less, summarizes earlier)

Not compacting when expected:

Check /context-stats to see current usage
Verify enabled: true in config
Check logs for [context-compactor] messages

Characters per token wrong:

Default of 4 works for English
Try 3 for CJK languages
Try 5 for highly technical content

Logs

Enable debug logging:

{
  "plugins": {
    "entries": {
      "context-compactor": {
        "config": {
          "logLevel": "debug"
        }
      }
    }
  }
}

Look for:

[context-compactor] Current context: ~XXXX tokens
[context-compactor] Compacted X messages → summary