agentwit 0.2.0

Transparent proxy witness for AI agent ↔ MCP server communications

agentwit

Transparent witness for AI agent ↔ MCP server communications

日本語版 / Japanese

What is agentwit?

agentwit is a transparent proxy that sits between AI agents and MCP servers, recording every communication as a tamper-proof witness log.

Unlike existing tools that act as "guards" (blocking suspicious traffic), agentwit acts as a "witness" — it never blocks, never interferes, but records everything with cryptographic chain integrity.

Guard vs. Witness

Tool	Approach	Blocks traffic	Tamper-proof log
mcp-scan	Proxy + Guard	✅	❌
Proximity	Static scanner	—	❌
Intercept	Policy proxy	✅	❌
agentwit	Witness proxy	❌	✅

How it works

AI Agent
   │
   ▼
agentwit proxy  ◄── records every message with chain hash
   │                 never blocks, fully transparent
   ▼
MCP Server       ◄── zero modification required

Each recorded event is chained to the previous one via SHA-256:

genesis_hash = sha256("genesis:" + session_id)
      │
      ▼
event_1:  session_chain = sha256(genesis_hash  +  hash(event_1))
      │
      ▼
event_2:  session_chain = sha256(event_1_chain +  hash(event_2))
      │
      ▼
     ...

Any single-byte modification to any event breaks the entire chain from that point forward — making tampering immediately detectable.

Quick Start

Installation

pip install agentwit

1. Start the witness proxy

agentwit proxy --target http://localhost:3000 --port 8765
# Starting agentwit proxy → http://localhost:3000
# Listening on 127.0.0.1:8765
# Session: ./witness_logs/session_20260314_120000

2. Point your agent to the proxy

# Before: http://localhost:3000
# After:  http://localhost:8765
# That's it. No other changes needed.

3. Generate an audit report

agentwit report --session ./witness_logs/session_20260314_120000 \
                --format html --output report.html

4. Verify chain integrity

agentwit replay --session ./witness_logs/session_20260314_120000
# Session: session_20260314_120000  (6 events)
# Chain integrity: VALID

Commands

agentwit proxy   --target URL [--port 8765] [--log-dir ./witness_logs] [--actor NAME]
agentwit report  --session DIR [--format json|markdown|html] [--output FILE]
agentwit replay  --session DIR [--verify/--no-verify]
agentwit diff    --session-a DIR --session-b DIR

Command	Description
proxy	Start the transparent witness proxy
report	Generate audit report (json / markdown / html)
replay	Replay and verify chain integrity of a session
diff	Compare two sessions side by side

Witness Log Format

Each intercepted event is stored as one JSON line in witness.jsonl:

{
  "witness_id":      "sha256 of the entire signed event",
  "session_chain":   "sha256(prev_chain_hash + event_hash)",
  "timestamp":       "2026-03-14T12:18:53.708937+00:00",
  "actor":           "demo-agent",
  "action":          "tools/call",
  "tool":            "bash",
  "input_hash":      "sha256 of the input payload",
  "output_hash":     "sha256 of the output payload",
  "full_payload":    { "params": {}, "result": {} },
  "risk_indicators": [
    { "pattern": "shell_exec", "severity": "high", "matched": "bash" }
  ]
}

Events are appended to a JSONL file as they arrive — the proxy never buffers or delays the upstream response.

Tamper Detection

Modify any field in the log and agentwit detects it immediately:

# Simulate tampering: change "actor" in event[0]
python3 -c "
import json; lines=open('witness.jsonl').readlines()
e=json.loads(lines[0]); e['actor']='ATTACKER'
lines[0]=json.dumps(e)+'\n'; open('witness.jsonl','w').writelines(lines)
"

agentwit replay --session ./witness_logs/session_20260314_120000
# Session: session_20260314_120000  (6 events)
# Chain integrity: TAMPERED
#   [event 0] FAIL - session_chain mismatch:
#     expected '0fd4d24bcb3dab7d171e…'
#     got      'a79a9e4cdb19795a521e…'

Use Cases

• Security engineers auditing AI agent behavior in production
• Enterprise teams requiring AI activity compliance logs
• AI researchers reproducibly comparing agent sessions
• Penetration testers documenting MCP tool usage as evidence

Python API

from agentwit import WitnessLogger, ChainManager

# Direct logging (no proxy needed)
logger = WitnessLogger(session_dir="./logs", actor="my-agent")
event = logger.log_event(
    action="tools/call",
    tool="bash",
    full_payload={"params": {"command": "ls"}, "result": {"stdout": "..."}}
)
logger.close()

# Verify a recorded session
chain = ChainManager(session_id="session_20260314_120000")
results = chain.verify_chain(events)
all_valid = all(r["valid"] for r in results)

Requirements

• Python 3.10+
• FastAPI, uvicorn, httpx, click (installed automatically)

License

MIT © agentwit contributors