# ExactGround: stop AI coding agents from installing packages that do not exist

**ExactGround is a free, open-source guard for AI coding agents (Claude Code, Codex, Gemini CLI, Cursor).** It checks every `npm`/`pnpm`/`yarn`/`bun`/`npx` and `pip`/`uv`/`poetry`/`pdm`/`pipx` install, and every new dependency written into a manifest, against the public npm registry and PyPI before the command runs. It blocks:
- package names that do not exist (hallucinated packages, the root of "slopsquatting");
- versions that were never published;
- young or little-used look-alikes of popular packages;
- npm security placeholders.

It has zero dependencies, runs locally and is MIT-licensed. An optional hosted API also answers "does this function exist in *this* version?".

[![CI](https://github.com/alidaram99/exactground/actions/workflows/ci.yml/badge.svg)](https://github.com/alidaram99/exactground/actions/workflows/ci.yml) · Website: https://alidaram99.github.io/exactground/ · Hosted API: https://apify.com/dropin-apis/exactground-api

```console
$ npx -y github:alidaram99/exactground check pypi:requests pypi:reqeusts pypi:huggingface-cli react@99.0.0
OK      pypi:requests
BLOCK   pypi:reqeusts — "reqeusts" does not exist on PyPI; did you mean "requests"? (it is 1 edit away)
BLOCK   pypi:huggingface-cli — "huggingface-cli" does not exist on PyPI
BLOCK   react@99.0.0 — version 99.0.0 of "react" was never published (latest is 19.3.0)
```

## Why this matters

- **Package hallucination is common and repeatable.** The USENIX Security 2025 study *We Have a Package for You!* generated 2.23 million code samples with 16 models. **19.7% referenced at least one package that does not exist** (205,474 unique names). 43% of hallucinated names reappeared on all 10 reruns of the same prompt ([paper](https://www.usenix.org/conference/usenixsecurity25/presentation/spracklen)).
- **Slopsquatting** turns that into an attack: someone registers the invented name with malware, and the next agent that runs `pip install <invented-name>` installs it ([Wikipedia](https://en.wikipedia.org/wiki/Slopsquatting); [CSA research note, 2026](https://labs.cloudsecurityalliance.org/research/csa-research-note-slopsquatting-ai-supply-chain-20260419-csa/)). `huggingface-cli` (above) is the classic example: a name models invent for the real `huggingface_hub[cli]`.
- **Agents install without a human looking.** A rule like "don't invent packages" in `CLAUDE.md` or `AGENTS.md` is text the model may ignore, especially after context compaction. A hook is code that runs every time.

## Quick start

Node.js 20 or newer. No install needed:

```sh
npx -y github:alidaram99/exactground check left-pad expresss pypi:numpy==1.26.4
npx -y github:alidaram99/exactground scan "npm i zod react-hook-formz && pip install -r requirements.txt"
npx -y github:alidaram99/exactground manifest package.json
```

For hooks, use a local checkout (faster, and no download on every tool call):

```sh
git clone --depth 1 --branch v0.1.0 https://github.com/alidaram99/exactground.git ~/tools/exactground
```

## Add it to your coding agent

`exactground init <agent>` prints the exact config with absolute paths for your checkout. `--write` merges it into the current project and keeps your existing hooks.

### Claude Code (plugin)

```sh
claude plugin marketplace add alidaram99/exactground
claude plugin install exactground@exactground-marketplace
```

The plugin registers a `PreToolUse` hook on `Bash|Write|Edit|MultiEdit`.
- A blocked install is denied with the reason shown to Claude, for example: *"reqeusts" does not exist on PyPI; did you mean "requests"?*
- Warnings are allowed and passed to Claude as context.

Manual alternative: `node ~/tools/exactground/bin/exactground.mjs init claude --write`.

### Codex

```sh
codex plugin marketplace add alidaram99/exactground --ref v0.1.0
```

Install the plugin, then review and trust the hook in `/hooks`; Codex only runs trusted hooks. Manual alternative: `exactground init codex --write` writes `.codex/hooks.json`, with `PreToolUse` on `Bash` and `apply_patch`, so patches that add dependencies to `package.json`, `requirements.txt` or `pyproject.toml` are checked too.

### Gemini CLI

`exactground init gemini --write` adds a `BeforeTool` hook for `run_shell_command|write_file|replace` to `.gemini/settings.json`.

### Cursor

`exactground init cursor --write` adds a `beforeShellExecution` hook to `.cursor/hooks.json`. Cursor cannot block file edits before they happen, so ExactGround catches the follow-up `npm install`/`pip install`/`uv sync` instead: a bare install checks every manifest dependency that is not yet in the lockfile.

## What it checks

| Situation | Verdict |
|---|---|
| Name not on npm/PyPI (`npm i reacct-dom`, `pip install reqeusts`) | **block**, with "did you mean" |
| Pinned version never published (`react@99.0.0`, `numpy==9.9`) | **block** |
| npm security placeholder (`0.0.1-security`: malware was removed) | **block** |
| Look-alike of a top-3,000 package that is < 180 days old or < 500 weekly downloads | **block** |
| Look-alike that is old and widely used | warn |
| Published < 30 days ago, < 500 weekly downloads, deprecated, or yanked | warn |
| Registry unreachable | allowed with a warning (`--strict` or `"strict": true` blocks) |
| `--index-url`/`--extra-index-url` in use (private packages possible) | missing names only warn |

**Where it looks:**
- direct installs;
- `npx`/`pnpm dlx`/`bunx`/`uvx` runs;
- `pip install -r` files, including nested `-r`;
- bare `npm install`/`yarn`/`pnpm install`/`uv sync`/`poetry install` (dependencies missing from the lockfile);
- `Write`/`Edit` of `package.json`, `requirements*.txt` and `pyproject.toml`;
- Codex `apply_patch`.

Commands wrapped in `bash -lc "…"` are unwrapped.

**Configuration:** optional `.exactground.json` at the project root:

```json
{ "allow": ["my-internal-lib", "pypi:corp-utils"], "privateScopes": ["@acme"], "strict": false, "newPackageDays": 30, "lowDownloads": 500 }
```

Lookups are cached for 24 hours in `~/.cache/exactground` (misses for 30 minutes, so a name registered later is noticed).

## Version-exact API checks (hosted, pay per check)

Most hallucinations are real packages used wrongly: `useActionState` in a React 18 project, or `numpy.asfarray` after NumPy 2.0 removed it. The [ExactGround API](https://apify.com/dropin-apis/exactground-api) answers those questions from the published package itself: npm `.d.ts` via the TypeScript compiler, and Python wheels parsed statically, without running any code. It is an MCP server:

```sh
claude mcp add --transport http exactground https://dropin-apis--exactground-api.apify.actor/mcp --header "Authorization: Bearer $APIFY_TOKEN"
```

| Tool | Price |
|---|---|
| `check_symbols` | $0.002 per symbol |
| `check_packages` | $0.0005 per package |
| `check_diff` | $0.01 per diff (every import added by a change) |

From the CLI: `APIFY_TOKEN=… exactground api check_symbols '{"ecosystem":"pypi","package":"numpy","version":"2.1.0","symbols":["numpy.asfarray"]}'`.

## How it compares

| Tool | What it does | Blocks a hallucinated install inside the agent? | Version-exact API check? |
|---|---|---|---|
| **ExactGround** | Registry reality + typosquat signals in agent hooks (free); API checks (hosted) | **Yes**: Claude Code, Codex, Gemini CLI, Cursor hooks | **Yes** (hosted API) |
| [Socket Firewall](https://docs.socket.dev/docs/socket-firewall-overview) | Proxy that blocks confirmed malware at install time | Malware yes; a non-existent name simply fails to install (or installs a fresh squat until it is confirmed) | No |
| [Context7](https://context7.com/) | Puts version-specific docs into the prompt | No; the agent can still invent names | No; documentation text, not a yes/no check |
| `npm audit` / `pip-audit` | Known vulnerabilities in installed packages | No; runs after install, on packages that exist | No |
| Type checkers (`tsc`, `pyright`) | Exact API checks for typed code after install | No | Yes, but only after code and environment exist |

These work together. ExactGround is the cheap gate in front of the install, and Socket and audits cover the security of real packages.

## FAQ

### How do I stop Claude Code from installing hallucinated npm or PyPI packages?

Install the ExactGround Claude Code plugin (two commands above). Its `PreToolUse` hook checks the package names in every Bash install command and every `package.json`/`requirements.txt`/`pyproject.toml` edit, and denies the tool call if a name does not exist.

### What is slopsquatting?

Registering a package name that AI models hallucinate, so that agents and developers who trust the suggestion install the attacker's code. The term was coined by Seth Larson; the USENIX 2025 study measured how often models invent names.

### Does ExactGround send my code anywhere?

The local guard sends only package names to the public registries (`registry.npmjs.org`, `api.npmjs.org`, `pypi.org`), the same requests your package manager makes. The hosted API receives only what you send to it.

### Will it block my private packages?

Not if you list them in `.exactground.json` (`allow` or `privateScopes`). A missing name only warns when pip/uv use a custom `--index-url`.

### Does it slow the agent down?

A check is one cached HTTP request per new package name, usually 100–400 ms, and nothing for commands that do not install anything.

### Is a hook a security boundary?

No. Agent hooks are guardrails. Claude Code and Codex document that hooks can time out or be bypassed, Codex hosted tools are not hooked, and Cursor cannot block file edits before they happen. ExactGround fails open on internal errors and registry outages unless you set `strict`. Keep lockfiles, CI checks and an install-time scanner too.

### Which ecosystems are supported?

npm (npm, pnpm, yarn, bun, npx) and PyPI (pip, uv, poetry, pdm, pipx, uvx).

## Development

```sh
npm test        # 27 offline tests: parser, policy, cache, all four hook formats, manifests, patches
```

Popular-package lists come from [npm-high-impact](https://github.com/wooorm/npm-high-impact) (MIT) and [top-pypi-packages](https://hugovk.github.io/top-pypi-packages/) (see `data/`).

## License

MIT. Not affiliated with npm, PyPI, Anthropic, OpenAI, Google or Cursor.