Post to Mastodon from Codex

Codex drafts it. You approve it. PostDelegate posts it.Mastodon: Posts and threads on mastodon.social, with images or a video.

How to post to Mastodon from Codex

Add PostDelegate to Codex. Add the server to ~/.codex/config.toml as below. Run codex mcp login postdelegate and sign in in your browser.
~/.codex/config.toml
```
[mcp_servers.postdelegate]
url = "https://app.postdelegate.com/mcp-oauth-dynamic"
```
Connect Mastodon in PostDelegate. On the calendar page choose Add Channel, then Mastodon. Sign in to your mastodon.social account and approve the permissions PostDelegate asks for: reading your profile, publishing posts and uploading media.
Ask Codex for a draft. Describe the post in plain words. Codex checks your Mastodon channel's rules, creates the post and sends back a preview link.

Teach Codex the posting rules

Add PostDelegate’s AGENTS.md to your repository, so Codex knows the MCP tools, the REST API and the safety rules when it works there. Agent files has the steps.

What to ask Codex

Mention any Mastodon setting in plain words and Codex fills it in. Codex can also read text files in your project, such as a changelog or a draft in Markdown.

Draft a Mastodon post about our open-source release, under 500 characters, with two relevant hashtags.
Which Mastodon posts do I have scheduled next week? Move nothing, just list them.
Summarise the README’s “Why” section as a Mastodon thread and save it as a draft.

What Codex can do on your Mastodon channel

Check the rules first. Before writing, it reads your Mastodon channel's length limit (500 characters) and required settings.
Draft, schedule or post. It creates a draft, a scheduled post or an immediate post, and runs the same checks as the app.
Use your media. It attaches files from your media library or adds one from a public link.
Review and fix. It lists what is scheduled, changes the Mastodon settings of a post that has not gone out, and deletes posts you no longer want.

A Mastodon post is up to 500 characters with up to four images or one video. PostDelegate keeps the text and media together with the planned post, publishes it as a public post at the time you pick, and turns extra entries into a thread of replies.

Before you start

PostDelegate connects accounts on mastodon.social. Accounts on other Mastodon servers cannot be connected yet.
Posts are published as public posts, limited to 500 characters with up to four images or one video.

The Mastodon channel guide has every field, and MCP tools lists exactly what an assistant can and cannot do.

Questions

Will Codex publish to Mastodon without asking me?

Not unless you ask it to. Ask for a draft and the post waits on your calendar until you schedule it, and your workspace's approvals apply as usual. Tools that change data are marked as such, so Codex can ask you before it schedules or deletes anything.

Do I need an API key to connect Codex?

No. Codex signs in with your PostDelegate account through your browser. An API key is only for clients that cannot sign in, as described in MCP clients.

Does it cost extra to use Codex with PostDelegate?

No. The MCP server is on every plan, and Codex runs on your own Codex account, so PostDelegate never charges for AI. Every plan starts with a 7-day free trial with no card.

Can Codex attach images or video to a Mastodon post?

It can use files already in your media library, or add one from a public link. It cannot fetch files from your computer, so upload those in the app first. See MCP tools.

Can I connect an account on another Mastodon server?

Not yet. PostDelegate connects accounts on mastodon.social. Accounts on other Mastodon servers cannot be connected today.

Can I schedule a Mastodon thread?

Yes. Add more entries to the post with Add post in a thread, and they are published as replies to the first post.

Mastodon from other assistants

Other networks from Codex

Prefer to plan Mastodon posts yourself? See the Mastodon scheduler.