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Connect ChatGPT & Claude.ai to Lawbster

Browser clients like ChatGPT and Claude.ai support MCP servers as "custom connectors" with OAuth out of the box — no code, no plain-text token, everything in the browser.

Prerequisites

  • ChatGPT Pro / Team / Enterprise or Claude.ai Pro / Max / Team / Enterprise
  • A Lawbster account → 14 days free
  • Logged into Lawbster in the same browser (for the OAuth sign-in click)

Why OAuth instead of an API key?

Browser clients shouldn't store plain-text tokens. The OAuth flow obtains a short-lived JWT that's auto-refreshed. Safer and more convenient — no API-key handling.

ChatGPT (Pro / Team / Enterprise)

  1. Settings → Connectors → Add custom connector
  2. Name: Lawbster
  3. MCP Server URL: https://lawbster.planitprima.com/mcp
  4. Authentication: OAuth
  5. Save → a browser tab opens → sign in to Lawbster → Allow

Done. Lawbster shows up as a tool source in any new chat. Toggle it on in the Tools dropdown — ChatGPT now calls legal_search, legal_lookup etc. whenever they fit.

Claude.ai (Pro / Max / Team / Enterprise)

  1. Settings → Connectors → Add custom
  2. Name: Lawbster
  3. Remote MCP server URL: https://lawbster.planitprima.com/mcp
  4. Sign in → sign in to Lawbster → Allow

In any chat: tools icon → enable Lawbster. Bonus: Claude.ai supports resources — legal://rechtsrahmen and friends show up as attachable references.

Test

Ask ChatGPT or Claude:

What does Art. 6 GDPR require for processing personal data? Please cite the provisions.

The assistant calls legal_lookup with Art. 6 GDPR, returns the full text with all paragraphs, possibly enriched with legal_get_context for Art. 5 and Art. 7.

What happens during OAuth?

The client runs a standard OAuth 2.1 authorization-code flow against Lawbster's identity provider, verifies your login and obtains a short-lived JWT access token (plus refresh token). The token is stored encrypted in the connector store and refreshed automatically — nobody sees the plain text.

Before each tools/call, the JWT is sent to Lawbster, validated against the identity provider's public key set, and counted against the per-seat quota.

Seats and OAuth

Each OAuth subject (= your Lawbster login) counts as a separate seat — same as an API key. If you connect Lawbster in both ChatGPT and Claude.ai with the same Lawbster identity, that's one seat (same subject_id in the quota counter).

Troubleshooting

Connector shows 'Connection failed'

OAuth flow incomplete — sign in again. Sometimes it helps to log out of Lawbster in the browser and back in.

Tools aren't being called

In ChatGPT: open the Tools dropdown, enable Lawbster. ChatGPT only calls tools that are explicitly enabled for the session (default behaviour for custom connectors since November 2025).

401 after a while

Refresh token expired. Run the sign-in flow again.

Next steps: Tool reference · Resources · FAQ