Caushell

Compiler-style pre-execution safety analysis for Harness shell actions.

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Quick start ·

Configuration ·

What Caushell catches ·

Working with sandboxes ·

How it works

Caushell (causal + shell) runs between a Harness and the local shell. Before a shell action reaches the local shell, Caushell performs pre-execution semantic analysis.

Shell action → AST → command modeling → session execution graph → safety analysis → decision

It preserves command structure, data flow and state changes across commands, and context such as paths, variables, working directory, and Git state. It also emits reviewable structured evidence for debugging, policy extension, and audit.

What Caushell catches

Caushell decides based on the actual impact a shell action can have on the local environment. It covers common risk classes such as:

• Blocking catastrophic deletion or overwrite of critical targets such as system directories, disks, and partitions
• Requiring approval when remote content flows into a shell or interpreter
• Recognizing dangerous shell actions generated under the influence of untrusted context
• Requiring approval for operations that can destroy the Git worktree, index, branches, or stash
• Recognizing the actual impact of variable expansion, globbing, redirection, pipelines, and working directory changes

The examples below show the default policy. Each check produces exactly one final decision.

| Risk | Harness shell action | Default decision |

| --- | --- | --- |

| Normal inspection command | ls src | Allow |

| File mutation outside the workspace | rm /tmp/other/file | NeedApproval |

| Remote content execution | curl https://example.com/install.sh \| bash | NeedApproval |

| Git local state discard | git reset --hard HEAD~1 | NeedApproval |

| Git untracked file deletion | git clean -fdx | NeedApproval |

| Relative path delete after cd / | cd / && rm -rf etc | Deny |

| System path deletion | rm -rf /etc/* | Deny |

| Disk / partition overwrite | sudo dd if=image.iso of=/dev/sda | Deny |

Working with sandboxes

Caushell handles pre-execution analysis, while a sandbox enforces runtime restrictions. They can be used together.

1. Protecting workspace and Git state

Development workflows usually require a sandbox to allow workspace reads and writes as well as Git commands. Under this configuration, git reset --hard can still discard local work; Caushell can require confirmation or block the action before execution.

2. Identifying file use and data flow

A sandbox can control file read and write permissions, but the risk of a file also depends on how it is used. The same read or write creates different risk relationships when it involves a normal project file, remotely downloaded content, input from outside the workspace, startup configuration, or sensitive configuration. Whether the content flows to the network also affects the decision.

Tests or local runs may need to read .env, while dependency installation or API calls also require network access. Reading sensitive configuration and sending its contents to a remote endpoint forms an exfiltration chain; Caushell can use taint analysis to identify these shell-visible data flows.

3. Making decisions before the process starts

Runtime sandboxing blocks a process after it starts and reaches a restricted boundary. Caushell returns a decision before the shell action executes.

For a combined command, pre-execution analysis can identify a later high-risk operation before the entire action starts, avoiding the execution of earlier commands. It can also require confirmation or block the action before the process produces side effects.

Quick start

Install the Caushell runtime:

curl -fsSL https://github.com/fatmo666/Caushell/releases/latest/download/install.sh | bash
export PATH="$HOME/.local/bin:$PATH"

Stable releases are published from v* tags. The installer downloads the latest stable GitHub release by default. To pin a version, set CAUSHELL_VERSION, for example CAUSHELL_VERSION=v0.0.9.

Prebuilt releases support Linux x86_64 as a static binary, macOS x86_64, and Apple Silicon. Windows and Linux ARM64 do not have prebuilt packages yet.

Then install the corresponding Harness integration. In Codex and Claude Code, these integrations are installed as plugins.

Codex

codex plugin marketplace add fatmo666/Caushell
codex plugin marketplace upgrade caushell
codex plugin add caushell-codex@caushell

Check the installation:

caushell doctor codex

This checks the installed binaries, hook wrapper, runtime/config compatibility, and daemon state. runtime daemon is down is only a warning before the first Harness shell action.

To verify the Codex integration more deeply, run:

caushell doctor codex --smoke

The smoke test checks that Codex sees the enabled caushell-codex plugin, then sends harmless synthetic PreToolUse and PostToolUse hook events through the installed Caushell hook. The success signal is Result: OK.

For normal Codex use, review and trust the Caushell hook in /hooks if Codex asks you to do so.