Claude Code vs OpenCode Plugin Systems

Side-by-side comparison of hook/plugin extensibility between Claude Code (Anthropic) and OpenCode (opencode.ai).

Claude Code vs OpenCode Plugin Systems

Side-by-side comparison of hook/plugin extensibility between Claude Code (Anthropic) and OpenCode (opencode.ai).

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Architecture Comparison

Dimension	Claude Code	OpenCode
Extension format	Shell commands in settings.json	JS/TS modules (npm or local files)
Install mechanism	Manual config edit	npm auto-install (Bun) at startup
Hook surface	PreToolUse, PostToolUse, Stop, Notification	30+ events across tools, sessions, files, LSP, TUI
Compaction control	None (not exposed)	experimental.session.compacting hook — inject context or replace entire prompt
Custom tools	Via MCP server (separate setup)	Native plugin registration
Env var injection	Via shell hook	shell.env hook
File protection	Via PreToolUse hook	tool.execute.before + explicit check
Load order	Settings hierarchy	Global config → project config → global dir → project dir
Language constraint	Any (shell)	JavaScript/TypeScript
State access	None (pure side effects)	client, project, $ (Bun shell), directory, worktree

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Compaction Hook — The Key Differentiator

OpenCode’s experimental.session.compacting hook fires before the LLM generates a continuation summary. No Claude Code equivalent exists.

Use case 1 — Inject domain state:

"experimental.session.compacting": async (input, output) => {
  output.context.push(`
## Task State
Currently implementing: auth middleware refactor
Files in progress: src/auth/middleware.ts, src/auth/session.ts
Last completed: extracted session validation to SessionService
Next: add rate limiting
  `)
}

Use case 2 — Replace entire compaction prompt:

"experimental.session.compacting": async (input, output) => {
  output.prompt = `
You are generating a continuation for a multi-agent task.
Summarize: current task, files modified, blockers, next steps.
Format for a new agent to resume work immediately.
  `
}

This allows implementing custom Context Compression Strategies strategies (anchored iterative summarization, opaque compression) at the harness level, not the system prompt level. Claude Code users must approximate this via CLAUDE.md instructions to the model — less reliable because the model can ignore prose instructions under context pressure.

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Custom Tools

Claude Code approach: Register an MCP server, configure it in settings, start it as a separate process. Full tool available to the model.

OpenCode approach: Declare a tool inside a plugin module, automatically available on next startup:

tool: {
  mytool: tool({
    description: "Fetch PR status from Linear",
    args: { prId: tool.schema.string() },
    async execute(args, { directory }) {
      // linear API call
      return JSON.stringify(result)
    }
  })
}

OpenCode’s approach is lower friction for simple custom tools; MCP is better for complex, reusable tool servers.

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Event Coverage

Claude Code’s four events (PreToolUse, PostToolUse, Stop, Notification) cover the core tool execution loop. OpenCode’s 30+ events cover the full session lifecycle — including LSP diagnostics, TUI interactions, and permission decisions. This matters for:

• Observability: react to session.diff to log what the agent changed
• Security: intercept permission.asked to audit what the agent is requesting
• Integration: fire on file.edited to trigger external sync

For most developer workflows, Claude Code’s four events are sufficient. OpenCode’s broader surface is useful for building production harnesses or complex integrations.

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When to Use Each

Claude Code hooks are sufficient for:

• Pre/post tool filtering and logging
• Stop-event notifications
• Simple env var injection via shell hooks

OpenCode plugins add value for:

• Custom compaction strategies (inject task state into context summaries)
• Custom tools without MCP overhead
• Observability hooks (session diffs, LSP diagnostics)
• Multi-agent session coordination via session events

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Related Pages

• OpenCode — OpenCode entity page
• Claude Code Plugins — Claude Code plugin system detail
• Context Compression Strategies — what compaction hooks extend
• Agent Harness — both systems are harness implementations