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Security·6 min·

Agent Wallet Security: Spending Limits, Monitoring, and Controls

How to secure autonomous agent spending with per-wallet limits, transaction caps, freeze controls, and real-time monitoring.

What is agent wallet security? It's the set of controls — spending limits, per-transaction caps, freeze controls, and real-time monitoring — that keep autonomous agent spending safe. Mithril provides these guardrails so you can give agents financial autonomy without runaway risk.

The Risk Model

Autonomous agents introduce new financial risks:

  • Runaway spending: An agent in a loop could make thousands of API calls
  • Prompt injection: A malicious input could instruct the agent to spend on unintended services
  • Logic errors: A bug in agent code could cause excessive spending
  • Credential theft: If an API key is leaked, an attacker could spend from the credit line

    • Defense in Depth

    Mithril provides multiple layers of protection:

    Layer 1: Per-Transaction Limits

    Set a maximum amount for any single API call. If an x402 service quotes a price above this limit, the transaction is rejected.

    Recommended starting point: $1 per transaction (most x402 calls cost $0.001-0.10).

    Layer 2: Daily Spending Caps

    Set a maximum total spend per wallet per day. Once reached, all further transactions are blocked until the next day.

    Recommended starting point: $5-10/day per agent during testing, $50-100/day in production.

    Layer 3: Credit Line Limits

    The overall credit line caps total exposure. Even if daily limits are generous, the credit line provides an absolute ceiling.

    Layer 4: Instant Freeze

    Any wallet can be frozen from the dashboard with one click. The agent immediately loses the ability to spend. Unfreeze when you're ready.

    Layer 5: Real-Time Monitoring

    The dashboard shows:

  • Live transaction feed per agent
  • Daily and monthly spend totals
  • Spend by service category
  • Unusual activity alerts

    • Best Practices

  • One wallet per agent. Never share wallets. This ensures clean audit trails and isolated freeze controls.
  • Start conservative. Begin with low limits and increase as you gain confidence in agent behavior.
  • Review weekly. Check transaction logs for patterns — unusually high call volumes, unexpected services, or cost spikes.
  • Rotate API keys. Regenerate Mithril API keys periodically, especially if team members leave.
  • Use environment variables. Never hardcode API keys in source code or agent prompts.
  • Test with low limits first. Deploy new agents with $1/day limits. Verify behavior before increasing.

    • Incident Response

    If you suspect unauthorized spending:

  • Freeze the wallet immediately from the dashboard
  • Review transaction logs to identify unauthorized calls
  • Rotate the API key to prevent further access
  • Adjust limits before unfreezing
  • Contact team@trymithril.com if you need help investigating

    • The Bottom Line

    Agent autonomy and security aren't in conflict. With proper spending limits, monitoring, and freeze controls, you can give agents real financial autonomy while maintaining full control.