sansin-core

Local-first AI agent safety engine. Score tool calls, learn from corrections, zero cloud dependency.

Thompson Sampling + context-aware heuristics. Ships with pre-trained priors so it works out of the box. Runs anywhere Python runs, stdlib only, no API keys.

pip install sansin-core

Quick Start

from sansin_core import SansinLocal

gate = SansinLocal()

# Score a tool call
decision = gate.check("send_email", {"recipients": 500, "irreversible": True})
print(decision.allow)        # False
print(decision.risk_score)   # 0.9
print(decision.reason)       # "deny"

# Override to teach the engine
gate.override(decision.id, "allow", "approved by admin")

# Next time, the engine remembers
decision = gate.check("send_email", {"recipients": 500})
# risk_score is now lower — it learned

How It Works

Every tool call gets a risk score from 0.0 (safe) to 1.0 (dangerous).

Heuristics classify tools by keyword. read_file starts low-risk. delete_database starts high-risk. Context modifiers like {"recipients": 500} or {"irreversible": True} push scores higher.

Thompson Sampling learns from your corrections. Override a blocked call with "allow" and the engine updates its Beta distribution for that tool. After ~10 overrides per tool, learned behavior starts blending with heuristics. After ~50, the engine mostly trusts what it learned from you.

Community priors ship with the package (15 common tools, ~20-override quality each). New installs aren't starting from zero.

MCP Safety Proxy

Drop-in firewall between any MCP client and upstream server. The agent never knows Sansin exists.

pip install sansin-core[mcp]
sansin-mcp-proxy --upstream stdio://npx -y @modelcontextprotocol/server-filesystem /tmp

Point your MCP client at the proxy instead of the upstream server. Every tool call is scored before forwarding. High-risk calls are blocked with an explanation.

The proxy exposes three management tools (configurable prefix, default sansin_):

• sansin_override — override a blocked decision
• sansin_status — view engine statistics and per-tool priors
• sansin_decisions — list recent decisions for auditing

# Custom prefix to avoid collisions
sansin-mcp-proxy --upstream stdio:///path/to/server --prefix safety_

# Fail-closed mode for regulated environments
sansin-mcp-proxy --upstream stdio:///path/to/server --fail-closed

Interactive Demo

See the learning engine in action with 50 simulated decisions:

sansin-demo

Watches Thompson Sampling learn in real-time with ASCII confidence bars.

API Reference

SansinLocal(db_path, fail_closed, load_community)

gate.check(tool_name, context) -> Decision

Score a tool call. Returns immediately.

decision = gate.check("delete_file", {"path": "/etc/passwd"})
decision.allow          # bool — should the call proceed?
decision.risk_score     # float 0.0-1.0
decision.safe_probability  # float — P(safe) from Thompson Sampling
decision.certainty      # float — how confident the engine is
decision.reason         # str — "allow", "escalate", or "deny"
decision.id             # str — UUID for override reference

gate.override(decision_id, correct_action, reason) -> bool

Teach the engine. correct_action must be "allow" or "block".

gate.status() -> dict

Engine statistics: decision counts, per-tool priors (alpha, beta, override count).

gate.export_priors(path) / gate.import_priors(path)

Export/import learned priors as JSON. Share across machines or teams.

Design Decisions

Fail-open by default. A safety product that breaks your agent's workflow gets uninstalled. Fail-closed mode is available for regulated environments.

Context-aware keywords. "write" is medium-risk by default. It only escalates to high-risk when combined with blast radius modifiers like "all", "every", "bulk", "batch", "mass" in the context.

SQLite WAL mode. Thread-safe, handles concurrent reads with a single writer. Good for <50 tool calls/second, which covers every local agent use case.

Zero required dependencies. The core engine uses only Python stdlib. MCP proxy is an optional extra (pip install sansin-core[mcp]).

Requirements

• Python 3.10+
• No required dependencies (stdlib only)
• Optional: mcp>=1.2.0 for MCP proxy

License

MIT. See LICENSE.

Links

• Documentation
• GitHub
• PyPI
• Sansin Cloud