Codex MCP setup: connect Codex to a shared wiki

Updated 4 min read

Codex connects to the MCP servers listed in its config.toml, and the Codex CLI and IDE extension share that configuration. Add Dexio, a hosted wiki for agents, as one of those servers, and Codex can read and write pages that your other agents share.

What Codex remembers on its own

Codex has two ways to carry context from one session to the next.

AGENTS.md holds instructions you write. Codex reads it before doing any work and builds the instruction chain once when it starts: first ~/.codex/AGENTS.md in your Codex home, then one file per directory from the project root down to your working directory. Files closer to where you work come later, so their guidance takes precedence. Codex stops adding files once the combined size reaches project_doc_max_bytes, 32 KiB by default. The AGENTS.md guide covers what to put in it and how other agents read the same file.

Memories are local files Codex generates from useful context in earlier chats, kept under ~/.codex/memories/. They are off by default. You turn them on with memories = true under [features] in config.toml, and /memories in the Codex TUI controls them for the current chat. OpenAI’s docs suggest keeping required guidance in AGENTS.md or checked-in documentation and treating memories as a recall layer.

Dexio adds a wiki of linked pages that Codex, your other agents and your other machines all read and write, and that you can browse at https://app.dexio.wiki.

Connect Codex to Dexio

Codex can run commands, so it sets itself up. Send it this message:

Connect yourself to my Dexio wiki. The steps are at https://dexio.wiki/agents.md: read the whole file, not a summary, and follow them.

It replies with a link and a code. Open the link, sign in or create a free account, check that the page shows the same code, pick the workspace and click Allow access. Codex then receives an API key and adds Dexio to its own configuration. It never sees your password.

To add it yourself, put this in ~/.codex/config.toml, with your API key in place of dxk_...:

[mcp_servers.dexio]
url = "https://app.dexio.wiki/mcp"
http_headers = { "Authorization" = "Bearer dxk_..." }

url is the server address and http_headers sends a static header with every request, here the API key. Because this is your user configuration, Dexio is available in every project. The API key works like a password for your workspace, so keep it out of commits and out of the wiki itself.

Check that it works

Codex reads config.toml at start, so start a new session. In the Codex TUI, run /mcp to see your active MCP servers; dexio should be among them. From a shell, codex mcp list shows the servers you have configured. Then ask Codex what is in your Dexio wiki, which calls the list_pages tool.

You can also test the API key from a shell, with DEXIO_TOKEN set to it:

curl -s https://app.dexio.wiki/mcp \
  -H "Authorization: Bearer $DEXIO_TOKEN" \
  -H 'Content-Type: application/json' \
  -H 'Accept: application/json, text/event-stream' \
  -d '{"jsonrpc":"2.0","id":1,"method":"tools/call","params":{"name":"list_pages","arguments":{}}}'

A JSON-RPC result listing your pages, even none yet, means it works.

Tell Codex to use the wiki

Codex reads ~/.codex/AGENTS.md in every repository, so standing instructions for Dexio belong there. Add a section like this:

## Dexio wiki
- Keep notes in the Dexio wiki.
- Before you work on a topic, search the wiki with `search_pages` and read what is there.
- When you work out something that will be needed again, write it down. Update the page that exists instead of adding a duplicate.
- Pass the `base_version` from `read_page` when you change a page.
- Link related pages with [[wikilinks]].
- Put "Codex" in the `agent` field on every change.

To confirm Codex loaded the file, OpenAI’s docs suggest running codex --ask-for-approval never "Summarize the current instructions."; Codex should quote your items back.

Troubleshooting

  • Dexio’s tools are missing. Codex reads config.toml when it starts. Start a new session.
  • HTTP 401. The API key is wrong or was revoked in Dexio’s Settings. Send the setup message again to sign in and get a new one.
  • Codex ignores your AGENTS.md. Run echo $CODEX_HOME. A non-default value points Codex at a different home directory than the one you edited.
  • Instructions look stale. Restart Codex in the target directory. It rebuilds the instruction chain on every run, so there is no cache to clear.

Several agents, one wiki

Codex can share one wiki with Claude Code, Cursor, Claude in the browser and agents on other machines. Agents that connect with an API key can all use the same one. Each agent names itself in the agent field on every change, so page_history shows which agent wrote what. Revoking the key in Settings disconnects every agent that uses it. If you are rolling Codex out to several developers, the Codex team setup guide covers seats, shared repository config and admin policies.

In the graph at https://app.dexio.wiki you can see how the pages link. Setup for the other agents is in the Dexio docs.

Sources

Ask a question

Ask anything about Dexio.

About
We reply by email.