Trust Scoring¶

Missy tracks the reliability of providers, MCP servers, and tools using a 0--1000 trust score. The score adjusts automatically based on observed behavior: successful operations increase trust, while failures and policy violations decrease it.

Score Scale¶

New entities start at 500 (neutral). The score is clamped to the [0, 1000] range.

Score Adjustments¶

Three event types modify trust scores, each with a configurable weight:

Trust Threshold¶

The is_trusted() method checks whether an entity's score exceeds a threshold (default: 200):

from missy.security.trust import TrustScorer

scorer = TrustScorer()

# After some operations...
if not scorer.is_trusted("mcp_server__risky_tool"):
    # Warn or block
    logger.warning("Low trust score for risky_tool")

When an entity drops below the trust threshold, the agent runtime can:

• Log a warning in the audit trail
• Require human approval before using the entity
• Skip the entity in favor of a more trusted alternative

Integration with the Tool Loop¶

The TrustScorer is consulted during the agent's tool execution loop:

flowchart TD
    A[Tool Call Requested] --> B{Check Trust Score}
    B -->|Above threshold| C[Execute Tool]
    B -->|Below threshold| D[Warn / Require Approval]
    C -->|Success| E[record_success +10]
    C -->|Failure| F[record_failure -50]
    C -->|Policy Violation| G[record_violation -200]
    D -->|Approved| C
    D -->|Denied| H[Skip Tool]

1. Before executing a tool or calling a provider, the runtime checks is_trusted(entity_id).
2. If the score is below the threshold, the operation may be blocked or escalated to the ApprovalGate.
3. After execution, the appropriate record_* method is called to update the score.

Tracked Entities¶

Trust scores are tracked for any entity identifier. Common patterns:

Viewing Scores¶

All current scores can be retrieved programmatically:

scorer.get_scores()
# {"provider:anthropic": 620, "mcp:github": 380, ...}

Resetting Scores¶

To reset an entity back to the default score of 500:

scorer.reset("mcp:github")