How do I install the NPM Exists skill?

Run npx skillmds@latest add mearman/npm-exists in your terminal (requires Node.js), paste this page's agent-chat prompt into Claude, Cursor, or any MCP-connected agent, or download the SKILL.md file and copy it into your agent's skills directory.

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This skill is tagged as working with Claude Code, Claude.ai, OpenAI Codex. SKILL.md is an open format, so most agents that read a skills directory can load it too.

Is NPM Exists free to use?

Yes. Installing skills from SkillMD is free, and the skill stays under its author's original license.

Who published NPM Exists?

Mearman (@mearman) published this skill. Their other Agent Skills are listed on their SkillMD profile.

NPM Exists by mearman — Agent Skill

Name: NPM Exists
Author: Mearman

File contents

Check npm Package Existence

Check if a package name exists in the npm registry.

Usage

npx tsx scripts/exists.ts <package-name> [options]

Arguments

Argument	Required	Description
`package-name`	Yes	The exact package name to check (case-sensitive)

Options

Option	Description
`--no-cache`	Bypass cache and fetch fresh data from API

Output

Package exists:

✓ Package "react" exists
  URL: https://www.npmjs.com/package/react
  Published: Yes

Package does not exist:

✗ Package "my-awesome-pkg-12345" does not exist
  The name is available for use

Script Execution (Preferred)

npx tsx scripts/exists.ts <package-name> [options]

Options:

--no-cache - Bypass cache and fetch fresh data from API

Run from the npm-registry plugin directory: ~/.claude/plugins/cache/npm-registry/

Existence Check API

HEAD https://registry.npmjs.org/{package}

Parameters

Parameter	Required	Description
`package`	Yes	The exact package name to check (case-sensitive)

Examples

Check if a package exists:

HEAD https://registry.npmjs.org/react

For scoped packages:

HEAD https://registry.npmjs.org/@babel/core

Response Interpretation

Package exists - HTTP 200 OK

The package is published and available
You can use npm info or npm install with this name

Package does not exist - HTTP 404 Not Found

The package name is available for use
No package with this exact name exists in the registry

Before publishing a new package, verify the name is available:

npx tsx exists.ts my-new-package

Validate Package Name

Confirm a package exists before installing or using it:

npx tsx exists.ts some-dependency

Scoped Packages

Check scoped package names:

npx tsx exists.ts @myorg/package-name

Naming Rules

Package names must:

Start with a letter, number, @, or _
Contain only URL-safe characters (letters, numbers, hyphens, underscores)
Not start with . or _
Not contain spaces
Not exceed 214 characters
Not be the same as a node.js/core module name

Scoped packages (@scope/name) have additional rules:

Scope must be the username of the npm owner
Scope must be followed by a slash

Caching

Existence checks are cached for 1 hour. Package availability changes infrequently, so short cache times provide a good balance between freshness and performance.

Use the --no-cache flag to bypass the cache.

Use npm-info to get detailed package metadata when it exists
Use npm-search to find similar or alternative packages
Use npm-downloads to see package statistics

Error Handling

Network errors: The npm registry may be temporarily unavailable. Retry after a brief delay.

Rate limiting: While existence checks use HEAD requests (minimal bandwidth), excessive rapid requests may be rate-limited.

Scoped packages: Remember that scoped packages require the full name including the scope (e.g., @babel/core, not just core).

---name: npm-existsdescription: Check if an npm package name exists in the registry. Use when the user asks if a package name is available, wants to check package existence, or verify if a package is published.---# Check npm Package ExistenceCheck if a package name exists in the npm registry.## Usage```bashnpx tsx scripts/exists.ts <package-name> [options]```### Arguments| Argument | Required | Description ||----------|----------|-------------|| `package-name` | Yes | The exact package name to check (case-sensitive) |### Options| Option | Description ||--------|-------------|| `--no-cache` | Bypass cache and fetch fresh data from API |### OutputPackage exists:```✓ Package "react" exists URL: https://www.npmjs.com/package/react Published: Yes```Package does not exist:```✗ Package "my-awesome-pkg-12345" does not exist The name is available for use```## Script Execution (Preferred)```bashnpx tsx scripts/exists.ts <package-name> [options]```Options:- `--no-cache` - Bypass cache and fetch fresh data from APIRun from the npm-registry plugin directory: `~/.claude/plugins/cache/npm-registry/`## Existence Check API```HEAD https://registry.npmjs.org/{package}```### Parameters| Parameter | Required | Description ||-----------|----------|-------------|| `package` | Yes | The exact package name to check (case-sensitive) |### ExamplesCheck if a package exists:```HEAD https://registry.npmjs.org/react```For scoped packages:```HEAD https://registry.npmjs.org/@babel/core```## Response Interpretation**Package exists** - HTTP 200 OK- The package is published and available- You can use `npm info` or `npm install` with this name**Package does not exist** - HTTP 404 Not Found- The package name is available for use- No package with this exact name exists in the registryBefore publishing a new package, verify the name is available:```bashnpx tsx exists.ts my-new-package```### Validate Package NameConfirm a package exists before installing or using it:```bashnpx tsx exists.ts some-dependency```### Scoped PackagesCheck scoped package names:```bashnpx tsx exists.ts @myorg/package-name```## Naming RulesPackage names must:- Start with a letter, number, `@`, or `_`- Contain only URL-safe characters (letters, numbers, hyphens, underscores)- Not start with `.` or `_`- Not contain spaces- Not exceed 214 characters- Not be the same as a node.js/core module nameScoped packages (`@scope/name`) have additional rules:- Scope must be the username of the npm owner- Scope must be followed by a slash## CachingExistence checks are cached for 1 hour. Package availability changes infrequently, so short cache times provide a good balance between freshness and performance.Use the `--no-cache` flag to bypass the cache.## Related- Use `npm-info` to get detailed package metadata when it exists- Use `npm-search` to find similar or alternative packages- Use `npm-downloads` to see package statistics## Error Handling**Network errors**: The npm registry may be temporarily unavailable. Retry after a brief delay.**Rate limiting**: While existence checks use HEAD requests (minimal bandwidth), excessive rapid requests may be rate-limited.**Scoped packages**: Remember that scoped packages require the full name including the scope (e.g., `@babel/core`, not just `core`).

Frequently asked questions

NPM Exists