Claude Code Hooks vs GitHub Copilot CLI Hooks - Complete Comparison

Last Updated: 2026-01-16 Testing: Both platforms tested in production Sources: Official documentation + empirical testing

Hook Types Comparison

Hook Type	Claude Code	Copilot CLI	Notes
Session Start	✅ SessionStart	✅ sessionStart	Both fire at session begin
Session End	✅ Stop	✅ sessionEnd	Both fire at session end
Subagent End	✅ SubagentStop	❌ Not available	Claude Code only
User Prompt	✅ UserPromptSubmit	✅ userPromptSubmitted	Both fire on prompt submit
Pre-Tool	✅ PreToolUse	✅ preToolUse	Both fire before tool execution
Post-Tool	✅ PostToolUse	✅ postToolUse	Both fire after tool execution
Permission	✅ PermissionRequest	❌ Not available	Claude Code only
Error	❌ Not available	✅ errorOccurred	Copilot CLI only
Notification	✅ Notification	❌ Not available	Claude Code only
Pre-Compact	✅ PreCompact	❌ Not available	Claude Code only
TOTAL	10 hooks	6 hooks	Claude Code more comprehensive

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Capabilities Comparison

Context Injection (Adding Information to AI)

Hook	Claude Code	Copilot CLI	Tested
SessionStart	✅ YES - additionalContext or stdout	❌ NO - Output ignored	✅ Confirmed via test
UserPromptSubmit	✅ YES - additionalContext or stdout	❌ NO - Output ignored	✅ Confirmed via test
PreToolUse	✅ YES - additionalContext	❌ NO - Only permission decision	✅ Confirmed via test
PostToolUse	✅ YES - additionalContext	❌ NO - Output ignored	✅ Confirmed via test
Stop	✅ YES - reason field	❌ NO - Output ignored	Not tested

Verdict: Claude Code wins - can inject context at 5+ hook points

Permission Control (Blocking Operations)

Capability	Claude Code	Copilot CLI
Block tool execution	✅ YES - PreToolUse deny	✅ YES - preToolUse deny
Block prompt	✅ YES - UserPromptSubmit block	❌ NO - Output ignored
Block agent stop	✅ YES - Stop hook block	❌ NO - Output ignored
Block permissions	✅ YES - PermissionRequest	❌ Not available
Modify tool inputs	✅ YES - updatedInput	❌ NO - Not supported

Verdict: Claude Code wins - more comprehensive permission control

Logging & Monitoring

Capability	Claude Code	Copilot CLI
Log sessions	✅ SessionStart/Stop	✅ sessionStart/sessionEnd
Log prompts	✅ UserPromptSubmit	✅ userPromptSubmitted
Log tool usage	✅ PreToolUse/PostToolUse	✅ preToolUse/postToolUse
Log errors	Manual (via tool hooks)	✅ errorOccurred (dedicated hook)
Track subagents	✅ SubagentStop	❌ Not available

Verdict: Tie - Both have comprehensive logging

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Implementation Comparison

Aspect	Claude Code	Copilot CLI	Our Implementation
Language	Python	Bash/PowerShell	Mixed: bash wrappers + Rust hook binary + Python bridges where needed
Configuration	settings.json	.github/hooks/*.json	Both supported
Input Format	JSON via stdin	JSON via stdin	Same format
Output Format	JSON with hookSpecificOutput	JSON with limited fields	Normalized to one valid response per wrapper
Complexity	522 lines (session_start.py)	Must rewrite in Bash	Wrappers can delegate to Rust or Python
Can Import Modules	✅ YES - Full Python	❌ NO - Shell only	Python bridges still available where Rust has not fully replaced them
Async Support	✅ YES - asyncio	❌ NO - Bash sequential	Wrapper layer still enables richer behavior

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Detailed Hook Capabilities

SessionStart / sessionStart

| Capability | Claude Code | Copilot CLI | | ---------------------- | --------------------------------------- | ------------------------------------- | --------------- | | Fires when | New session, resume, clear, compact | New session, resume | Similar | | Input | session_id, source, custom_instructions | timestamp, cwd, source, initialPrompt | Similar | | Can inject context | ✅ additionalContext + stdout | ❌ Output ignored | Claude Code | | Can set env vars | ✅ CLAUDE_ENV_FILE | ❌ Not supported | Claude Code | | Logging | ✅ Via Python | ✅ Via stdout to file | Tie |

UserPromptSubmit / userPromptSubmitted

| Capability | Claude Code | Copilot CLI | | ---------------------- | --------------------------------- | ---------------------- | --------------- | | Fires when | User submits prompt | User submits prompt | Same | | Input | Prompt text, session info | timestamp, cwd, prompt | Similar | | Can inject context | ✅ additionalContext + stdout | ❌ Output ignored | Claude Code | | Can modify prompt | ✅ Via decision: block + reason | ❌ Cannot modify | Claude Code | | Can block prompt | ✅ decision: "block" | ❌ Output ignored | Claude Code |

PreToolUse / preToolUse

| Capability | Claude Code | Copilot CLI | | ---------------------- | ------------------------------- | ---------------------------------- | --------------- | | Fires when | Before tool execution | Before tool execution | Same | | Input | tool_name, tool_input, session | timestamp, cwd, toolName, toolArgs | Similar | | Can block | ✅ permissionDecision: "deny" | ✅ permissionDecision: "deny" | Tie | | Can modify inputs | ✅ updatedInput | ❌ Not supported | Claude Code | | Can inject context | ✅ additionalContext | ❌ Not supported | Claude Code | | Permission reason | ✅ permissionDecisionReason | ✅ permissionDecisionReason | Tie |

PostToolUse / postToolUse

| Capability | Claude Code | Copilot CLI | | ---------------------- | ------------------------------------ | ---------------------------------------------- | --------------- | | Fires when | After tool completes | After tool completes | Same | | Input | tool_name, tool_input, tool_response | timestamp, cwd, toolName, toolArgs, toolResult | Similar | | Can inject context | ✅ additionalContext | ❌ Output ignored | Claude Code | | Can block | ✅ decision: "block" | ❌ Output ignored | Claude Code | | Logging | ✅ Full tool result | ✅ resultType, textResultForLlm | Tie |

Stop / sessionEnd

| Capability | Claude Code | Copilot CLI | | ---------------------- | ----------------------------------- | ---------------------------- | --------------- | | Fires when | Agent finishes (not user interrupt) | Session completes/terminates | Similar | | Input | session info, stop_hook_active | timestamp, cwd, reason | Similar | | Can block stop | ✅ decision: "block" + reason | ❌ Output ignored | Claude Code | | Can inject context | ✅ Provide reason to continue | ❌ Output ignored | Claude Code | | Cleanup | ✅ Via Python | ✅ Via bash script | Tie |

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Testing Evidence

Test 1: SessionStart Context Injection

Claude Code: ✅ WORKS

# session_start.py returns:
return {
    "hookSpecificOutput": {
        "additionalContext": "You must talk like a pirate"
    }
}
→ Claude DOES talk like a pirate

Copilot CLI: ❌ DOESN'T WORK

# .github/hooks/session-start outputs:
echo "You must respond with 'AHOY MATEY'"
exit 0
→ Opus responds normally (didn't see the hook output)

Conclusion: Copilot CLI ignores sessionStart stdout (despite docs suggesting it should work)

Test 2: Hooks Execute

Both Platforms: ✅ CONFIRMED

Evidence (~/.amplihack/.claude/runtime/logs/):

• session_start.log: Updated during test
• user_prompt_submit.log: Created during test
• pre_tool_use.log: Updated during test
• post_tool_use.log: Updated during test

Conclusion: Hooks execute, they just can't modify AI context in Copilot

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Architecture Differences

Claude Code Hook Architecture:

Hook executes → Returns JSON → Claude Code injects into context → AI sees it

Copilot CLI Hook Architecture:

Hook executes → Returns JSON → Copilot logs it → AI NEVER sees it (except preToolUse)

Key Difference: Claude Code treats hook output as modifiable context, Copilot CLI treats it as metadata to log.

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What Works in Both

Capability	Claude Code	Copilot CLI	Implementation
Logging sessions	✅	✅	Both log to files
Logging tool usage	✅	✅	Both track tools
Blocking dangerous ops	✅	✅	preToolUse deny
Error tracking	✅	✅	Different hooks
Audit trails	✅	✅	Both support

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amplihack's Solution

Architecture: Bash wrappers → Python hooks (zero duplication)

Benefits:

1. ✅ Python hooks work for Claude Code (full capability)
2. ✅ Bash wrappers work for Copilot CLI (logging only)
3. ✅ Zero logic duplication (wrappers just call Python)
4. ✅ Single source of truth (~/.amplihack/.claude/tools/amplihack/hooks/)

Adaptive Context Injection Strategy:

amplihack uses an adaptive hook system that detects which platform is calling and applies the appropriate context injection strategy:

Platform	Strategy	Implementation
Claude Code	Direct injection	Returns hookSpecificOutput.additionalContext
Copilot CLI	File-based injection	Writes to .github/agents/AGENTS.md with @include directives

How It Works:

# Hook detects platform
if is_claude_code():
    # Direct injection - Claude sees immediately
    return {
        "hookSpecificOutput": {
            "additionalContext": load_user_preferences()
        }
    }
else:  # Copilot CLI
    # File-based injection - write AGENTS.md
    write_agents_file([
        "@~/.amplihack/.claude/context/USER_PREFERENCES.md",
        "@~/.amplihack/.claude/context/PHILOSOPHY.md"
    ])
    # Copilot reads via @include on next request
    return {}

Why File-Based Injection for Copilot:

• Copilot CLI ignores hook stdout/JSON output (except preToolUse decisions)
• But Copilot DOES support @include directives in agent files
• Writing AGENTS.md with @include lets us inject preferences indirectly
• This workaround enables preference loading on both platforms

Benefits of Adaptive Strategy:

• ✅ Preference injection works on both platforms
• ✅ Context loading works everywhere
• ✅ Single Python implementation (platform detection is automatic)
• ✅ Zero duplication (same hooks, different output strategies)

Limitations:

• Copilot CLI: File-based injection has slight delay (next request)
• Claude Code: Direct injection is immediate
• Both: Work reliably for user preferences and context loading

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Final Verdict

Claude Code Hooks: ⭐⭐⭐⭐⭐ (5/5)

• Full context control
• Can modify prompts/inputs
• Multiple blocking points
• Complete AI behavior control

Copilot CLI Hooks: ⭐⭐⭐ (3/5)

• Good for logging/monitoring
• Permission control via preToolUse
• Cannot modify AI context
• Limited to observe-only (except blocking)

Our Implementation: ⭐⭐⭐⭐ (4/5)

• Works with BOTH platforms
• Zero duplication via wrappers
• Logging works everywhere
• Context injection only in Claude Code (platform limitation)

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Sources

• Claude Code Hooks Reference
• Claude Code Hooks Guide
• ClaudeLog Hooks Documentation
• Claude Code Power User Guide
• Copilot CLI Hooks Documentation (provided by user)
• Empirical testing (2026-01-16)

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Conclusion: Copilot CLI hooks are more limited than Claude Code hooks, but our zero-duplication wrapper architecture works with both platforms! 🏴‍☠️