Gummble MCP in Codex: Setup and Fixing OAuth Errors (2026)

How do you add Gummble MCP to Codex?

Run one command in your terminal:

codex mcp add gummble --url https://mcp.gummble.com/mcp

That is the entire setup. Codex detects that Gummble uses OAuth, opens your browser to sign in, and stores the connection. Once it is connected, Codex can search 300,000+ real app screens, 24,000+ flows, and real UX microcopy so it designs from shipped products instead of guessing. MCP access is included on every paid Gummble plan, and new accounts get a 7-day free trial.

Do not run codex mcp login gummble afterward. The add command already authenticated you. Running login again starts a second authorization and registers a redundant client on your account. One add is the whole job. This one point is the cause of most "why is Codex asking me to authorize twice" confusion.

The config.toml alternative

If you prefer to edit config directly, Codex stores MCP servers in ~/.codex/config.toml (global) or .codex/config.toml inside a trusted project. Add:

[mcp_servers.gummble]
url = "https://mcp.gummble.com/mcp"

Then authenticate once:

codex mcp login gummble

Use the add command or the config file, not both. The CLI add path is simpler because it handles OAuth for you.

Confirm it is connected

codex mcp list

Gummble should show as logged in. Inside the Codex TUI you can also run /mcp to see connected servers and their tools.

Fixing Codex MCP OAuth errors

Most Codex MCP problems are client-side and have a specific fix. Here is how to read the common ones.

"No authorization support detected" or "Auth: Unsupported"

This is a Codex client bug on older versions, not a server problem. Codex's HTTP client omitted a User-Agent header on its OAuth discovery request, which some CDNs and WAFs block, so Codex concluded the server had no OAuth and gave up. It is tracked in the openai/codex repo.

The fix is to update Codex to the latest version:

codex --version

Gummble's server advertises OAuth correctly, using the RFC 9728 protected-resource metadata that the MCP auth spec requires, served at https://mcp.gummble.com/.well-known/oauth-protected-resource/mcp. So once you are on a current Codex build, codex mcp add discovers the auth flow and signs you in. If you are stuck on an older Codex you cannot upgrade, the config.toml plus codex mcp login gummble path can also get past it.

"Codex asks me to authorize twice"

You ran both codex mcp add --url and codex mcp login. Each command runs its own OAuth flow, so you saw two browser prompts and two "Successfully logged in" messages. That is by design, not a bug. Use only codex mcp add gummble --url https://mcp.gummble.com/mcp and you authorize once.

"codex mcp not working" or "failed to start"

Check three things in order:

1. Run codex mcp list and confirm the URL is exactly https://mcp.gummble.com/mcp, with no trailing slash or typo.
2. Confirm you are on a paid Gummble plan. MCP is gated, so an unauthenticated or free-tier token is rejected. Start a free trial if you have not.
3. Re-authenticate: codex mcp login gummble. Tokens expire, and a stale token reads as a dead server.

"transport closed" or connection timeout

Gummble is a remote Streamable HTTP server, so a dropped connection is usually a network or proxy issue on your side. Retry the request, and if you are behind a corporate proxy, make sure mcp.gummble.com is reachable. If your OAuth provider needs a fixed callback port because of a firewall, set mcp_oauth_callback_port at the top level of config.toml.

Re-authenticating after a token expires

Run codex mcp login gummble to refresh. This is the one time running login on its own is correct: when you already added the server earlier and just need a fresh token.

What to do once it is connected

Prompt Codex with a research job, then let it pull references before it writes UI:

Use Gummble to find 5 mobile paywalls with annual-discount framing, then summarize how each one anchors value before price.

Use Gummble to find empty-state microcopy from fintech apps, then rewrite our "no transactions yet" screen in three of those voices.

That second prompt uses Gummble's microcopy search, which no other design MCP offers. For the full set of 10 copy-paste prompts across paywalls, onboarding flows, and UX writing, see How to Give Claude Code Real Design References. The same prompts work in Codex.

Frequently asked questions

Why does Codex ask me to authorize twice?

Because you ran codex mcp login after codex mcp add. The add command already authenticated you. Run only codex mcp add gummble --url https://mcp.gummble.com/mcp and you authorize once.

How do I fix "No authorization support detected" in Codex?

Update Codex to the latest version. The error is a client bug where Codex's OAuth discovery request was blocked by CDN bot protection. Gummble's server advertises OAuth correctly, so a current Codex connects without issue.

Where does Codex store MCP config?

In ~/.codex/config.toml for global servers, or .codex/config.toml inside a trusted project. Gummble's entry is [mcp_servers.gummble] with url = "https://mcp.gummble.com/mcp".

Do I need a paid plan to use Gummble MCP in Codex?

Yes. MCP access is included on all paid plans, starting at $9 per month, with a 7-day free trial for new accounts. See the Gummble MCP page.

Can Gummble MCP modify my files in Codex?

No. It is read-only. It exposes search tools such as gummble_search_screens, gummble_search_flows, and gummble_search_microcopy, with no write access.

Does this also work in Claude Code and Cursor?

Yes. Gummble MCP is a remote server that works with any MCP-compatible client. See the setup guide for Claude Code, Cursor, Windsurf, and v0, or compare against Mobbin MCP.

---

Published by the Gummble team. Codex commands, config paths, and the referenced openai/codex issue are accurate as of July 2026; Codex behavior changes between versions, so check codex --version if a command differs.