HALLUX

Check that a package, module or DOI exists in its registry before an agent installs, imports or cites it.

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What it can do

  • Hallux Check Command: Call this BEFORE running any command that installs a dependency: npm, yarn, pnpm, bun, pip, uv, poetry, pipx, cargo, go get, dotnet add package, nuget. Language models invent pla
  • Hallux Check: Does this identifier actually exist? Call before acting on any name you recalled rather than read: a package to install, a module to import, a DOI to cite. Returns one of: exists, deprec
  • Hallux Check Manifest: Call this after writing or editing a dependency file, and before committing it. Supported: package.json, requirements.txt, pyproject.toml, Cargo.toml, go.mod. Checks every depen

What data it sees

Do you need an account

No: the server works without sign-in

Check that a package, module or DOI exists in its registry before an agent installs, imports or cites it.

Covers npm, PyPI, crates.io, Go modules, Maven, NuGet and DOIs. Returns one of six verdicts: exists, deprecated, absent, phantom (a name models repeatedly invent), squat (such a name that someone has since registered) or unknown. A registry it cannot reach answers unknown, never a pass.

Tools: hallux_check_command (an install command, before it runs), hallux_check_manifest (a dependency file, after an edit) and hallux_check (identifiers directly).

No account and no key: the open tier allows 500 identifiers a day per client. Docs: https://blvkware.dev/hallux/

How to connect

How to connect HALLUX to Claude

The server address to paste into Claude settings:

https://hallux--blvkware.run.tools

  1. Open Claude (claude.ai or the desktop app).
  2. Go to Settings → Connectors.
  3. Click Add custom connector.
  4. Paste the server address copied below into Remote MCP server URL and click Add.
  5. In a chat, click + → Connectors and switch the new connector on.

Custom connectors are available on Free, Pro, Max, Team and Enterprise plans (Free is limited to one). On Team and Enterprise an organization Owner adds the connector first under Organization settings → Connectors.

Authorization

After you click Add, a sign-in window for the service opens. Sign in with your own account and approve access. Claude never sees your password.

How to connect HALLUX to ChatGPT

The server address to paste into ChatGPT settings:

https://hallux--blvkware.run.tools

  1. Open ChatGPT in a browser (chatgpt.com). A Plus, Pro, Business, Enterprise or Edu plan is required.
  2. Turn on developer mode once: Settings → Apps → Advanced settings → Developer mode.
  3. Open Settings → Connectors and click Create.
  4. Fill in the form: Name (anything), Description (one line about what the service does), MCP server URL (copy it below).
  5. Under Authentication choose OAuth if the service requires sign-in, otherwise None. Click Create.
  6. In a new chat open + → Apps/Connectors and enable the connector.

OpenAI has renamed this section before (Connectors → Apps/Plugins). If the label differs, search settings for "developer mode". On Business/Enterprise workspaces an admin must allow custom connectors first.

Authorization

On first use ChatGPT opens the service's sign-in window. Sign in and approve access.

How to connect HALLUX to Cursor

The server address to paste into Cursor settings:

https://hallux--blvkware.run.tools

Fastest: click Open in Cursor below and confirm the prompt.

Manually:

  1. In Cursor open Settings → Cursor Settings → MCP and click Add new global MCP server.
  2. Paste the JSON copied below into ~/.cursor/mcp.json (per project: .cursor/mcp.json in the repo root).
  3. Save the file. The server appears in the MCP list; authorize it there if asked.

Authorization

If the service needs sign-in, an authorize button appears next to the server in the MCP list.

Server tool list (4)

Raw names from tools/list. Only developers need these.

hallux_check_commandCall this BEFORE running any command that installs a dependency: npm, yarn, pnpm, bun, pip, uv, poetry, pipx, cargo, go get, dotnet add package, nuget. Language models invent plausible package names that have never existed, and attackers register those names because they can predict them. Installing one runs attacker code. You cannot tell the difference by looking at the name, which is why this check exists. Pass the command exactly as you intend to run it. The identifiers are extracted for you. If the result says BLOCK, do not run the command. Use the `successor` if one is given, otherwise tell the user what was found and stop.
hallux_checkDoes this identifier actually exist? Call before acting on any name you recalled rather than read: a package to install, a module to import, a DOI to cite. Returns one of: exists, deprecated, absent, phantom, squat, unknown. exists - proceed deprecated - proceed, but use `successor` absent - not in the registry. Do not proceed phantom - does not exist AND models repeatedly invent it. Do not proceed squat - was invented by models, then registered by someone. Treat as hostile unknown - could not verify. Never treat this as permission Live namespaces: cite.doi, pkg.crates, pkg.go, pkg.maven, pkg.npm, pkg.nuget, pkg.pypi. An unsupported namespace returns `unknown`, never an error, so it is safe to ask.
hallux_check_manifestCall this after writing or editing a dependency file, and before committing it. Supported: package.json, requirements.txt, pyproject.toml, Cargo.toml, go.mod. Checks every dependency in one pass, including dev and optional groups, which is where an invented name usually arrives.
hallux_watchRegister identifiers for notification when their verdict changes. The transition that matters is phantom to squat: a name models invent that somebody then registers. Use this for a dependency that came back `absent` or `phantom` and that the user intends to use anyway, or for a set of dependencies worth monitoring. Delivered by signed webhook to a URL you supply.