How to Open Claude: Web, Desktop, Mobile, and API

"How to open Claude" usually means one of two things: you want to start a chat session in your browser or app, or you're a developer trying to open a connection to Claude from your own code. Both are covered here, with the fastest path for each.

If you just want to chat, the shortest route is claude.ai in a browser or the official desktop/mobile app. If you want to call Claude from a script, backend, or product, you need an API key and an HTTP client — that's a different kind of "opening" and it's where most confusion actually happens.

Opening Claude in a Web Browser

This is the default way most people use Claude and requires no installation.

1. Go to claude.ai in any modern browser (Chrome, Firefox, Safari, Edge).
2. Sign in with an existing account, or create one with an email address or Google account.
3. Once logged in, you land directly in a new chat window — there's nothing else to configure.
4. Bookmark the URL or pin the tab if you use it daily.

If the page won't load, it's almost always one of three things: an ad blocker or privacy extension blocking scripts, a corporate network firewall restricting the domain, or a temporary outage on Anthropic's side. Try an incognito/private window first — it rules out extensions in about ten seconds.

Opening the Claude Desktop App

The desktop app (available for macOS and Windows) opens like any native application once installed:

1. Download the installer from Anthropic's official site.
2. Run the installer and grant any permissions requested (accessibility, notifications).
3. Launch it from your Applications folder, Start menu, or dock/taskbar.
4. Sign in with the same credentials you use on the web.

The desktop app keeps a persistent window, supports global keyboard shortcuts to summon it, and can stay running in the background — useful if you switch into Claude many times a day and don't want to reopen a browser tab each time.

Opening Claude on Mobile

The iOS and Android apps behave like the desktop app: install from the App Store or Google Play, sign in, and you're in a chat screen. If you already use Claude on the web, your conversation history syncs across devices as long as you're signed into the same account.

Opening Claude Programmatically (API Access)

This is where "opening Claude" changes meaning entirely. Instead of a UI, you're opening an HTTPS connection and sending structured requests. This is what you need if you're building a feature, an internal tool, or any product that calls Claude on a user's behalf.

The direct route is Anthropic's own API, which requires generating a key from a developer console, setting up billing, and handling streaming, tool calls, and rate limits yourself.

A faster route if you already have Claude access through a subscription is SubToAPI, which converts that access into a standard API key you can use in any HTTP client. Instead of managing a separate API billing relationship, you get a sub_live_... key and call a regular REST endpoint.

Opening a connection looks like this:

curl https://api.subtoapi.app/v1/messages \
  -H "Authorization: Bearer $SUBTOAPI_KEY" \
  -H "Content-Type: application/json" \
  -d '{
    "model": "claude-sonnet-4",
    "max_tokens": 512,
    "messages": [
      { "role": "user", "content": "Open a conversation and say hello." }
    ]
  }'

Or from JavaScript:

const res = await fetch("https://api.subtoapi.app/v1/messages", {
  method: "POST",
  headers: {
    "Authorization": `Bearer ${process.env.SUBTOAPI_KEY}`,
    "Content-Type": "application/json"
  },
  body: JSON.stringify({
    model: "claude-sonnet-4",
    max_tokens: 512,
    messages: [{ role: "user", content: "Open a conversation and say hello." }]
  })
});

const data = await res.json();
console.log(data);

That single POST request is the entire act of "opening" Claude from code — there's no session handshake or separate connect step. Every request is stateless and authenticated with your key.

To get set up: create an account at /signup, grab your key from the dashboard, and follow /docs/quickstart for a working example in under five minutes. Full endpoint details are in /docs/messages, and if you need real-time token-by-token output instead of a single response, see /docs/streaming.

Choosing the Right Way to Open Claude

| Use case | Best method | |---|---| | Quick question, casual use | Browser (claude.ai) | | Daily heavy use, want a dedicated window | Desktop app | | On the go | Mobile app | | Building a feature or automation | API (direct or via SubToAPI) | | Team needs shared usage tracking and seats | SubToAPI dashboard with per-member keys |

If you're choosing between managing your own API billing and using an existing subscription through SubToAPI, the deciding factor is usually whether you want a second billing relationship. SubToAPI plans start at €9/month (Solo), with Team at €19/seat and Scale at €49/seat for larger usage and more seats — see /pricing for the full breakdown. A free trial is available at signup so you can test the integration before committing.

Troubleshooting Common "Can't Open Claude" Issues

• Blank page or spinner that never loads: clear cookies for the domain or try a different browser profile.
• "Invalid API key" on first request: double-check you copied the full key including the sub_live_ prefix and that there's no trailing whitespace in your environment variable.
• Desktop app won't launch after install: on macOS, check Gatekeeper hasn't quarantined the app (System Settings → Privacy & Security); on Windows, run the installer as administrator.
• Works in browser but not in your script: this is almost always a missing or malformed Authorization header — confirm the exact format Bearer <key> with a space, not a colon.

Questions

Does "opening Claude" require an internet connection? Yes, for all methods — web, desktop, mobile, and API — Claude runs server-side, so an active connection is required even though the desktop and mobile apps feel local.

Can I open Claude without creating an account? No. Every access method, including the API, requires authentication — either a signed-in session for chat use or an API key for programmatic use.

What's the fastest way to open Claude from code if I already pay for a Claude subscription? Use SubToAPI: sign up at /signup, generate a key, and send your first request following /docs/quickstart — no separate API billing setup required.