Gummble MCP in Codex: Setup and OAuth Troubleshooting (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

On supported Codex versions, the client discovers Gummble OAuth and opens a browser authorization flow. Once connected, Codex can search 300,000+ real app screens, 21,000+ browsable flows, and real UX microcopy. MCP access is included on every paid Gummble plan; check the pricing page and checkout for current trial eligibility.

If codex mcp add already completed browser authorization, do not immediately run codex mcp login gummble as a second step. Use codex mcp list to inspect the connection first; run the separate login command only when the current Codex client reports that authorization is still required.

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"

This can happen when codex mcp login starts another browser flow after codex mcp add already completed authorization. Check codex mcp list after adding the server, and run the separate login command only when the client still reports that authorization is required.

"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. Check plan and trial eligibility if access is unavailable.
3. Re-authenticate: codex mcp login gummble. Tokens expire, and a stale token reads as a dead server.

"transport closed" or connection timeout

A dropped connection can come from client, network, proxy, authorization, or server state. Retry once, confirm mcp.gummble.com is reachable, and capture the Codex version and timestamp if it repeats. If your environment needs a fixed callback port because of a firewall, check the current Codex configuration documentation for mcp_oauth_callback_port support.

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 dedicated microcopy search. 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?

This can happen when a separate codex mcp login is run after codex mcp add already completed authorization. Inspect codex mcp list before starting another browser flow.

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

Update Codex, confirm the server URL, and retry OAuth discovery. If the error persists, capture the Codex version and timestamp for support; the message can reflect client-version, discovery, or network-policy differences.

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 $9.99 per month. Check the pricing page and checkout for current trial eligibility, then 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?

Gummble uses remote MCP, but client setup and OAuth support differ. See the current setup guide and verify the client-specific instructions before connecting. For plan and feature comparison, use the canonical Mobbin MCP alternative page.

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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.