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Live Dependency Resolver

LLMs have knowledge cutoff dates that are months old. When helping users install coding dependencies, this causes hallucinated version numbers, suggestions for deprecated packages, and incorrect install commands. This skill teaches agents to always verify packages against live registries before suggesting any installation - using CLI commands first for speed and simplicity, with web API fallback when CLI tools are unavailable.

When to use this skill

Trigger this skill when the user:

• Asks to install, add, or update any package or dependency
• Wants to check the latest version of a package
• Needs to scaffold a project with third-party dependencies
• Asks you to generate code that imports a third-party package
• Requests a package.json, requirements.txt, Cargo.toml, Gemfile, or go.mod
• Asks to compare package versions or check compatibility
• Mentions any package by name in a context where version matters

Do NOT trigger this skill for:

• OS-level packages (apt, brew, yum) - different registries and tools
• Private/internal registry packages - requires authentication, out of scope
• Post-install usage questions where the package is already installed and version is irrelevant

Key principles

1. Never trust your training data for versions - Your knowledge cutoff means every version number you "know" is potentially wrong. Always verify against the live registry before suggesting any version, even for well-known packages like React or Django.

2. CLI first, API fallback - Use CLI tools (npm view, pip index versions, cargo search, gem search, go list -m) as the primary lookup method. They're faster, work offline against local caches, and produce simpler output. Fall back to web APIs only when the CLI tool is unavailable or fails.

3. Verify package existence before recommending - Before suggesting an unknown or less-popular package, confirm it actually exists in the registry. A nonexistent package name in an install command wastes the user's time and erodes trust.

4. Show your work - When providing version information, include the command you ran and the raw output. This lets the user verify the result and learn the lookup method for future use.

5. Respect major version boundaries - Major version bumps often contain breaking changes. When a user's existing code targets v4.x, don't blindly suggest upgrading to v5.x. Flag major version differences and let the user decide.

Core concepts

Quick reference table

Decision tree

1. User mentions a package -> identify the ecosystem
2. Run the CLI command for that ecosystem
3. If CLI fails (tool not installed, network error) -> try the web API
4. If both fail -> tell the user you cannot verify and suggest they check manually
5. Never silently fall back to training data

Major version handling

When a user's project already pins to a major version (e.g. "react": "^17.0.0"), check whether the latest version is in the same major line. If it's a new major version, explicitly flag this: "The latest React is 19.x, but your project uses 17.x. Upgrading across major versions may require migration steps."

Common tasks

Check latest npm package version

# CLI (preferred)
npm view express version
# Returns: 4.21.2

# With more detail (all published versions)
npm view express versions --json

# Web API fallback
curl -s https://registry.npmjs.org/express/latest | jq '.version'

Gotcha: For scoped packages like @babel/core, the CLI works directly (npm view @babel/core version), but the API URL needs encoding: https://registry.npmjs.org/@babel%2fcore/latest.

Check latest Python package version

# CLI (preferred - requires pip 21.2+)
pip index versions numpy
# Output includes: LATEST: 2.2.3

# Web API fallback
curl -s https://pypi.org/pypi/numpy/json | jq '.info.version'

Gotcha: pip index versions requires pip 21.2+. On older pip versions, this command doesn't exist. Fall back to the PyPI JSON API. Also, always use python -m pip instead of bare pip to ensure you're targeting the correct Python installation, especially in virtual environments.

Check latest Go module version

# CLI (preferred - must be in a Go module directory)
go list -m golang.org/x/sync@latest
# Returns: golang.org/x/sync v0.12.0

# Web API fallback
curl -s https://proxy.golang.org/golang.org/x/sync/@latest | jq '.Version'

Gotcha: Go module paths are case-sensitive. github.com/User/Repo and github.com/user/repo are different modules. The Go proxy uses case-encoding where uppercase letters become ! + lowercase (e.g. !user/!repo).

Add a Rust crate dependency

# CLI: search for latest version
cargo search serde --limit 1
# Output: serde = "1.0.219"  # A generic serialization/deserialization framework

# CLI: add to project (cargo-edit required for older Rust, built-in since Rust 1.62)
cargo add serde --features derive

# Web API fallback
curl -s -H "User-Agent: live-dep-resolver" \
  https://crates.io/api/v1/crates/serde | jq '.crate.max_version'

Gotcha: cargo search output includes a description after the version. Parse carefully - extract just the version string within quotes. Also, crates.io API requires a User-Agent header or returns 403.

Check latest Ruby gem version

# CLI (preferred)
gem search ^rails$ --remote
# Output: rails (8.0.2)

# Web API fallback
curl -s https://rubygems.org/api/v1/gems/rails.json | jq '.version'

Gotcha: gem search without regex anchors (^...$) matches partial names. gem search rail returns dozens of gems. Always use ^name$ for exact matches.

Scoped npm packages and version ranges

# Check a scoped package
npm view @types/react version

# Check a specific version range's latest match
npm view react@^18 version
# Returns the latest 18.x version

# Check peer dependencies (important for plugin ecosystems)
npm view eslint-plugin-react peerDependencies --json

Python version compatibility check

# Check which Python versions a package supports
curl -s https://pypi.org/pypi/django/json | jq '.info.requires_python'
# Returns: ">=3.10"

# List all available versions to find one compatible with Python 3.9
pip index versions django
# Then check the classifiers for the specific version:
curl -s https://pypi.org/pypi/django/4.2.20/json | jq '.info.requires_python'

Anti-patterns