Dependency Verification Skill for Claude

> A package name the model produced is a claim, not a fact. The

> registry is the fact. Verify before you install.

Dependency Verification

Overview

Code-generating language models recommend packages that do not

exist at a measured rate of 5.2% (commercial models) to 21.7%

(open models) across 576,000 samples (Spracklen et al. 2024,

arXiv 2406.10279). Worse, 58% of hallucinated names recur across

reruns, so an attacker can predict them, register the empty name,

and ship malware. This is "slopsquatting." A proof-of-concept

package (huggingface-cli) drew over 30,000 downloads after being

registered against a commonly hallucinated name. Package

hallucination is also inversely correlated with coding-benchmark

score, so a better model does not make this go away.

The defense is cheap: confirm the name exists in its registry

before installing or recommending it. This skill defines that

check and is enforced by the guard_package_hallucination.py

PreToolUse hook.

When To Use

Apply before any of these:

• Running pip install, uv add, npm install, pnpm add,

yarn add, cargo add, poetry add, or pdm add.

• Writing a dependency into pyproject.toml, requirements.txt,

package.json, or Cargo.toml.

• Recommending a package to the user in prose.

When NOT To Use

• Bumping versions of packages already known to exist (use

sanctum:version-updates)

• Auditing a dependency's supply chain (use

leyline:supply-chain-advisory)

The Two Signals

A package fails verification on either signal:

• Nonexistent: the name is absent from its registry. This is

a likely hallucination. Do not install it. Search for the

correct name or confirm the package was renamed or removed.

• Typosquat / slopsquat: the name is one or two edits from a

popular package (for example reqeusts versus requests).

This is either a typo or a deliberate impersonation. Confirm

the exact name you intend before proceeding.

A name that is unknown to the bundled popular-package set but

present in the registry passes. A name that cannot be checked

because the registry is unreachable is reported as unverified,

never blocked: the guard does not fail closed on a network error.

A Confidence Signal, Not a Gate

Registry existence is the pass/fail check. Real-world usage is a

separate, softer signal that builds confidence on top of it. Once a

package clears the two signals above, cross-checking that it is

actually used by other projects raises your confidence that the name

is the established one rather than a freshly-registered impostor that

happens to exist.

Useful confidence signals, none of them blocking:

• GitHub dependents or code search hits for the exact package name

(an established package is imported across many repositories).

• Repository stars, recent commit activity, and release cadence on

the package's source.

• Download counts and publish history on the registry (a popular

name registered yesterday is a red flag; a modest name with years

of releases is reassuring).

Treat low usage as a prompt to look closer, never as a reason to

reject on its own. New, niche, internal, and private packages are

legitimately low-usage, so a missing GitHub footprint must not block

an install the registry already confirmed. Use this signal to build

confidence and to disambiguate between two similarly-named packages,

not to gate.

Verification Procedure

• Extract the exact package names the command or manifest edit

would fetch (strip version specifiers and flags).

• For each name, confirm existence in the registry. See

registry-checks.md for the

per-ecosystem endpoints and the offline-degradation rule.

• For any name close to a popular package, restate the intended

name and confirm it is the one you meant.

• Capture the verification as evidence (the registry URL and the

HTTP status) when the install lands in a PR, per

imbue:proof-of-work.

Relationship to the Guard Hook

The guard_package_hallucination.py hook runs this check

automatically on every Bash install command. Shadow mode (warn

only) is the default; set VOW_SHADOW_MODE=0 to block

typosquat and nonexistent installs. Disable the network lookup

with IMBUE_PKG_REGISTRY_CHECK=0 to rely on the offline

typosquat signal alone. The hook is a backstop, not a substitute:

verify deliberately when you add a dependency rather than waiting

for the gate.

Related Skills

• imbue:proof-of-work: capture the registry check as evidence.
• leyline:supply-chain-advisory: broader dependency supply-chain

auditing (lockfile drift, artifact integrity, bad versions).

Exit Criteria

• [ ] Every package in the install command or manifest edit is

confirmed present in its registry, or the install is

abandoned.

• [ ] Any name within two edits of a popular package is restated

and confirmed before install.

• [ ] A name that could not be verified online is reported as

unverified and not silently installed.

• [ ] For PR-bound installs, the registry check is captured as

proof-of-work evidence.