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.
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 |
| 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 |
Caushell handles pre-execution analysis, while a sandbox enforces runtime restrictions. They can be used together.
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.
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.
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.
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 plugin marketplace add fatmo666/Caushell
codex plugin marketplace upgrade caushell
codex plugin add caushell-codex@caushellCheck the installation:
caushell doctor codexThis 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 --smokeThe 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.
Codex hooks currently cannot ask for approval directly. When Caushell classifies a shell action as NeedApproval, the Codex integration blocks it by default and prints the reason. To let Codex run NeedApproval actions while still recording Caushell decisions, switch the Codex mode to observe:
caushell config set codex.need_approval_mode observeDeny decisions are always blocked.
claude plugin marketplace add fatmo666/Caushell
claude plugin marketplace update caushell
claude plugin install caushell-claude@caushell || claude plugin update caushell-claudeCheck the installation:
caushell doctor claudeThis 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 that Claude Code actually invokes the Caushell lifecycle hooks, run:
caushell doctor claude --smokeThe smoke test runs one harmless Claude Code Bash action and verifies that Caushell observed both PreToolUse and PostToolUse. The success signal is Result: OK.
Install the integration into each DSH profile you use:
# Web
dsh plugin --profile web add \
https://github.com/fatmo666/Caushell/releases/latest/download/caushell-dsh-bash.tgz
# TUI
dsh plugin --profile tui add \
https://github.com/fatmo666/Caushell/releases/latest/download/caushell-dsh-bash.tgz
# Headless
dsh plugin --profile headless add \
https://github.com/fatmo666/Caushell/releases/latest/download/caushell-dsh-bash.tgzPersistent Bash is not supported. See the DeepSeek Harness integration for source installation and configuration.
After the first installation, update Caushell with one command:
caushell updatecaushell --update is a compatible alias. The updater checks the release manifest, verifies the release checksum before replacing the runtime bundle, refreshes only enabled Codex or Claude Code plugins that are already installed, and runs a post-update doctor check. It never installs a Harness integration that you have not selected. Restart the active Harness after the update.
If an older installation reports unknown command: update, run the installer once more; subsequent updates can then use the built-in updater.
Useful variants:
caushell update --check # check the release manifest without changing files
caushell update --runtime-only # update runtime binaries only
caushell update --version v0.0.9 # pin a stable release tag
caushell build-info # show version, commit, release, and targetFor the configuration file location, configuration management commands, and user configuration fields, see:
- How Caushell works: the complete flow from a Harness shell action to the final decision
- Semantic model: Shell AST, command modeling, variable resolution, and the session execution graph
- Security model: risk analysis, Decision Assembly, and the Harness execution boundary
Caushell runs before every shell action, so latency is an important metric. Current measurements cover the Codex and Claude Code integrations.
| Item | Result |
|---|---|
| Latency | 1,000-command continuous test: Codex p95 3.10ms, Claude Code p95 3.05ms |
| Risk coverage | Remote content entering shell execution, catastrophic path deletion, disk/partition overwrite, xargs expansion, working directory changes, path/glob bypasses, destructive Git operations |
Caushell is available under the Apache License 2.0.
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