Hosted MCP: start succeeds, but navigate / observe immediately return No active session in ChatGPT custom app

[XxYouDeaDPunKxX]

Summary

I am using the Browserbase hosted MCP endpoint inside a ChatGPT custom app.

The start tool successfully creates a Browserbase session and returns a sessionId with available: true.

However, the next tool call immediately fails with:

No active session

This happens even on a simple public website, so it does not appear to be related to the target website, login walls, cookies, anti-bot behavior, or page complexity.

---

Endpoint shape tested

Hosted MCP endpoint:

https://mcp.browserbase.com/mcp?browserbaseApiKey=<REDACTED>

Also tested with:

https://mcp.browserbase.com/mcp?browserbaseApiKey=<REDACTED>&keepAlive=true

Same behavior in both cases.

No API keys, CDP URLs, signing keys, private session data, or target private pages are included in this report.

---

Reproduction steps

1. Configure Browserbase hosted MCP in a ChatGPT custom app using the hosted MCP URL.

2. Call the start tool.

3. start returns success, including:

   • a sessionId
   • available: true

4. Call navigate with a simple public URL:

   https://news.ycombinator.com/

5. navigate fails with:

   No active session

6. Call start again using the same returned sessionId.

7. start(sessionId) returns success again.

8. Call navigate again with the same public URL.

9. navigate still fails with:

   No active session

---

Actual behavior

The Browserbase session appears to be created or reused successfully by start, but subsequent tools such as navigate, observe, or extract do not see any active session.

Observed pattern:

start: success, sessionId returned, available: true
navigate: No active session
start(sessionId): success, same sessionId, available: true
navigate: No active session

---

Expected behavior

After start succeeds, subsequent Browserbase MCP tools in the same ChatGPT custom app interaction should be able to use the active Browserbase session.

Alternatively, if the active session must be selected or rebound explicitly, there should be a documented way to do that for tools such as navigate, observe, and extract.

---

Why this does not seem site-specific

The issue was reproduced with:

https://news.ycombinator.com/

This is a simple public page that does not require login.

So the problem appears to happen before any website-specific behavior is relevant.

---

Environment

• Browserbase hosted MCP endpoint
• Streamable HTTP / hosted MCP transport
• Client: ChatGPT custom app
• Tested with and without keepAlive=true
• Date tested: 2026-06-17

---

Possibly related area

This may be related to hosted MCP / Streamable HTTP session lifecycle behavior.

The specific symptom here is not a long-running session timing out.

Instead, the issue is immediate:

start succeeds, but the next tool call does not see an active session.

---

Questions

Could you confirm the intended behavior for hosted MCP in this flow?

1. Should start make the Browserbase session active for subsequent hosted MCP tool calls?
2. Is the ChatGPT custom app / MCP client expected to preserve any MCP session header or transport-level state between tool calls?
3. Is there a supported way to pass or select the Browserbase sessionId for navigate, observe, or extract?
4. Is keepAlive=true expected to affect active-session binding, or only Browserbase session lifetime?
5. Is this client flow currently supported with ChatGPT custom apps?

---

Security / privacy note

I have intentionally redacted all sensitive values.

This report does not include:

• Browserbase API keys
• CDP URLs
• signing keys
• real session IDs
• private target URLs
• user account information