Agentic Context Pruning (ACP)

Automatically reduces token usage in OpenCode by intelligently managing conversation context.

🤖 Agent Auto

ACP exposes pruning tools to manage context efficiently. Use these when context grows large.

Pattern formats: "start...end" (starts+ends), "start..." (starts), "...end" (ends), "exact" (contains)

When to use:

• discard — Completed tasks, noise, redundant outputs
• distill — Valuable context you want to preserve in summary form
• restore — Bring back previously pruned content if needed

⏩ Just Skip Reading This Readme

It's the Age of Agents

• Just paste this link into Open Code and ask it to explain.
• Ask why context pruning is important and how ACP helps save tokens.

Hey please read this readme and tell me why I should use ACP: https://raw.githubusercontent.com/tuanhung303/opencode-acp/master/README.md

👶 Context Pruning Features

🛠 Installation

👨‍💻 For Humans

Add to your OpenCode config:

// opencode.jsonc
{
    "plugin": ["@tuanhung303/opencode-acp@latest"],
}

Using @latest ensures you always get the newest version automatically when OpenCode starts. Restart OpenCode to begin.

🤖 For LLM Agents

Fetch this README and follow the instructions:

curl -s https://raw.githubusercontent.com/tuanhung303/opencode-acp/master/README.md

How ACP Works

ACP hooks into OpenCode's message flow to intelligently reduce context size before sending to the LLM:

flowchart LR
    subgraph OpenCode["OpenCode Core"]
        direction TB
        A[User Message] --> B[Session]
        B --> C[Transform Hook]
        C --> D[toModelMessages]
        D --> E[LLM Provider]
    end

    subgraph ACP["ACP Plugin"]
        direction TB
        C --> F[syncToolCache]
        F --> G[injectHashes]
        G --> H[Apply Strategies]
        H --> I[prune]
        I --> C
    end

    %% Arctic Clarity Color Palette (Lightened)
    style OpenCode fill:#F4F7F9,stroke:#5A6B8A,stroke-width:1.5px,color:#1E2A36
    style ACP fill:#E8F5F2,stroke:#9AC4C0,stroke-width:1.5px,color:#1E2A36
    style A fill:#FAFCFD,stroke:#D0D8E0,stroke-width:1px,color:#2D3E50
    style B fill:#FAFCFD,stroke:#D0D8E0,stroke-width:1px,color:#2D3E50
    style C fill:#FAFCFD,stroke:#D0D8E0,stroke-width:1px,color:#2D3E50
    style D fill:#FAFCFD,stroke:#D0D8E0,stroke-width:1px,color:#2D3E50
    style E fill:#FAFCFD,stroke:#D0D8E0,stroke-width:1px,color:#2D3E50
    style F fill:#F5FAF9,stroke:#A8C9C5,stroke-width:1px,color:#1E2A36
    style G fill:#F5FAF9,stroke:#A8C9C5,stroke-width:1px,color:#1E2A36
    style H fill:#F5FAF9,stroke:#A8C9C5,stroke-width:1px,color:#1E2A36
    style I fill:#F5FAF9,stroke:#A8C9C5,stroke-width:1px,color:#1E2A36

ACP uses multiple tools and strategies to reduce context size:

Tools

Discard — Exposes a discard tool that the AI can call to remove completed or noisy tool content from context.

Distill — Exposes a distill tool that the AI can call to distill valuable context into concise summaries before removing the tool content.

Strategies

Deduplication — Detects repeated tool calls with identical arguments (e.g., reading the same file multiple times) and retains only the most recent output. Earlier duplicates are replaced with lightweight placeholders. Runs automatically on every request with zero LLM cost.

Supersede Writes — Prunes write tool inputs when the same file has been subsequently read. The write content becomes redundant because the read output captures the current file state. Runs automatically on every request with zero LLM cost.

Purge Errors — Removes tool inputs for failed tool calls after a configurable turn threshold (default: 4). Error messages are preserved for debugging context, but potentially large input payloads are stripped. Runs automatically on every request with zero LLM cost.

Todo Reminder — Tracks todowrite activity and injects reminders when the agent neglects its task list. Helps maintain focus during long sessions by prompting the agent to review and update pending tasks.

Non-destructive: Your session history is never modified. ACP replaces pruned content with placeholders only in the request sent to your LLM.

Impact on Prompt Caching

LLM providers cache prompts using exact prefix matching—the KV (Key-Value) cache is reused only when the beginning of a new prompt is byte-for-byte identical to a cached prompt. Even a single character change invalidates the cache from that point forward.

When ACP prunes a tool output mid-conversation, it changes message content and invalidates cached prefixes from that point forward.

Trade-off: You lose some cache read benefits but gain larger token savings from reduced context size and improved response quality through reduced context poisoning. In most cases, the token savings outweigh the cache miss cost—especially in long sessions where context bloat becomes significant.

Note: In testing, cache hit rates were approximately 65% with ACP enabled vs 85% without.

Best use case: Providers that charge per-request (e.g., GitHub Copilot, Google Antigravity) see no negative price impact from cache invalidation.

Configuration

ACP uses its own config file:

• Global: ~/.config/opencode/acp.jsonc (or acp.json), created automatically on first run
• Custom config directory: $OPENCODE_CONFIG_DIR/acp.jsonc (or acp.json), if OPENCODE_CONFIG_DIR is set
• Project: .opencode/acp.jsonc (or acp.json) in your project's .opencode directory

{
    "$schema": "https://raw.githubusercontent.com/opencode-acp/opencode-acp/master/acp.schema.json",
    // Enable or disable the plugin
    "enabled": true,
    // Enable debug logging to ~/.config/opencode/logs/acp/
    "debug": false,
    // Notification display: "off", "minimal", or "detailed"
    "pruneNotification": "detailed",
    // Slash commands configuration
    "commands": {
        "enabled": true,
        // Additional tools to protect from pruning via commands (e.g., /acp sweep)
        "protectedTools": [],
    },
    // Protect from pruning for <turns> message turns
    "turnProtection": {
        "enabled": false,
        "turns": 4,
    },
    // Protect file operations from pruning via glob patterns
    // Patterns match tool parameters.filePath (e.g. read/write/edit)
    "protectedFilePatterns": [],
    // LLM-driven context pruning tools
    "tools": {
        // Shared settings for all prune tools
        "settings": {
            // Additional tools to protect from pruning
            "protectedTools": [],
        },
        // Removes tool content from context without preservation (for completed tasks or noise)
        "discard": {
            "enabled": true,
        },
        // Distills key findings into preserved knowledge before removing raw content
        "distill": {
            "enabled": true,
            // Show distillation content as an ignored message notification
            "showDistillation": false,
        },
        // Reminds agent to review/update todo list when stale
        "todoReminder": {
            "enabled": true,
            // Turns before first reminder (default: 12)
            "initialTurns": 12,
            // Turns between subsequent reminders (default: 6)
            "repeatTurns": 6,
        },
    },
    // Automatic pruning strategies
    "strategies": {
        // Remove duplicate tool calls (same tool with same arguments)
        "deduplication": {
            "enabled": true,
            // Additional tools to protect from pruning
            "protectedTools": [],
        },
        // Prune write tool inputs when the file has been subsequently read
        "supersedeWrites": {
            "enabled": false,
        },
        // Prune tool inputs for errored tools after X turns
        "purgeErrors": {
            "enabled": true,
            // Number of turns before errored tool inputs are pruned
            "turns": 4,
            // Additional tools to protect from pruning
            "protectedTools": [],
        },
    },
}

Commands

ACP exposes a /acp slash command with the following subcommands:

Turn Protection

Prevents tool outputs from being pruned for a configurable number of message turns. This buffer ensures the agent can reference recent outputs before they become eligible for pruning. Applies to both manual tools (discard, distill) and automatic strategies.

Todo Reminder

Monitors todowrite activity and injects reminders when the agent neglects its task list:

• Reminders are prunable like any other content
• Only triggers when pending or in_progress todos exist
• Resets on todowrite calls (todoread alone does not reset)

Protected Tools

These tools are always exempt from pruning across all strategies:

task, todowrite, todoread, discard, distill, batch, write, edit, plan_enter, plan_exit

Additional tools can be protected via protectedTools arrays in each config section.

Config Precedence

Settings merge in priority order (later overrides earlier):

Defaults → Global (~/.config/opencode/acp.jsonc) → Config Dir ($OPENCODE_CONFIG_DIR/acp.jsonc) → Project (.opencode/acp.jsonc)

Restart OpenCode after modifying configuration.

Limitations

Subagents — ACP is disabled for subagents. Subagent sessions prioritize returning concise summaries to the main agent over token efficiency. Pruning could interfere with this summarization behavior.

License

MIT