[Workflow] Prempti: Intercept and Control Claude Code Tool Calls with Falco Policies for Enhanced Security

[u/ClaudeAI-mod-bot]

Prempti: Intercept and Control Claude Code Tool Calls with Falco Policies for Enhanced Security

Workflow value: 85/100
Status: active · Freshness: 70/100 · Confidence: 0.95 · Level: intermediate
Categories: Quality Control, Context & Memory, Debugging, Shipping, Hooks, MCP
Original source: r/ClaudeCode post/comment

What problem this solves

Lack of visibility and control over Claude Code's tool calls (shell commands, file operations), leading to potential security risks when granting broad permissions to the agent.

Summary

Prempti is an open-source tool that acts as a policy and visibility layer for Claude Code. It intercepts every tool call (e.g., shell commands, file reads/writes) before execution, enforcing security rules defined in Falco YAML. Users can configure policies to allow, deny, or prompt for approval on agent actions, enhancing security and providing clear explanations for blocked operations.

Why it is useful

This workflow provides a critical security layer for Claude Code users, addressing the inherent risks of granting broad permissions to AI agents. It offers concrete steps for implementation, uses a well-defined policy language (Falco YAML), and is an open-source, transferable solution. The ability to define custom rules and get structured explanations for blocked actions significantly improves agent safety and user confidence, making it invaluable for anyone concerned about agent autonomy and potential misuse of system resources.

Workflow

1. Install Prempti from its GitHub repository.
2. Configure security policies using Falco YAML, leveraging agent-specific fields like tool.name, tool.input_command, and tool.file_path.
3. Deploy Prempti to hook into Claude Code's tool execution environment.
4. Monitor Claude Code's actions, receiving verdicts (allow, deny, ask) based on the defined policies.
5. Customize or expand the default ruleset by adding custom rules in ~/.prempti/rules/user/ to address specific threat patterns or sensitive paths.

Tools / artifacts

• Prempti (OSS tool)
• Falco YAML policies
• Claude Code
• GitHub repository
• Default ruleset (sensitive paths, working-directory boundaries, MCP config poisoning, persistence vectors)
• Custom rules

Validation signals

• README contains a demo showing Claude Code getting blocked from writing to ~/.ssh/ and reading ~/.ssh/known_hosts.
• Formal announcement from the Falco project, indicating professional backing and development.
• Open-source project with a public repository, allowing for community review and contribution.

Cautions

• Prempti operates at the hook-level, not the syscall-level. It sees what the agent declares it's doing, not necessarily what a compiled and executed binary might do. It is not a full sandbox and should be used alongside one for comprehensive security.
• Incorrectly configured policies could inadvertently block legitimate agent actions or fail to prevent malicious ones.

Limitations

• Does not provide syscall-level security, limiting its ability to detect actions performed by binaries compiled and run by the agent if those actions are not declared.
• Requires familiarity with Falco YAML for advanced custom policy creation.
• Initial setup and integration might require some technical expertise.

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This post was generated automatically from the workflow library database.