How to Post to Social Media with Grok (MCP Connector Guide)

Grok can write a post and put it on your calendar for X, LinkedIn, Threads, Instagram and four other networks, once you give it a PostAxis connector URL. Grok's connectors take a single URL with no sign-in step, so the URL carries a PostAxis API key, and that one detail shapes how you should set it up and look after it. This guide is for founders, marketers and anyone who already thinks out loud in Grok and wants the result to go out on schedule, not sit in a chat log.

Setup takes about three minutes. Most of this post is about what to do after that: prompts that work, what happens behind each one, and how to keep the key safe.

What you can automate with Grok

Grok is a chat assistant, so it shines at the writing and planning half of social media:

• Launch posts in several versions, a sharp line for X and a longer story for LinkedIn, scheduled together.
• A week of posts around one theme, shown to you as a list before anything is saved.
• Immediate updates like an outage all-clear on Telegram and a Facebook Page, published now.
• Photo posts for Instagram and Threads from an image you already host.
• Quick questions about your queue: "What goes out tomorrow?" or "Move Thursday's post to Friday."

What you need

• A PostAxis account. Every plan starts with a 7-day free trial.
• The PostAxis API add-on. Grok connects with an API key, and keys need the add-on.
• At least one social account connected under Accounts in PostAxis.
• Grok, with access to its connectors (custom MCP servers). Where the setting appears can depend on your plan and app version.

How to connect Grok to PostAxis (step by step)

1. Create your PostAxis account. Sign up at app.postaxis.io.

2. Connect your social accounts. Open Accounts in PostAxis and connect the networks you want Grok to use: Instagram, TikTok, YouTube, X, LinkedIn, Facebook, Threads or Telegram. Grok can only post to accounts connected here, and it never sees your social media passwords.

3. Create an API key. In PostAxis open Settings → API keys and click Create API key. Copy it right away; it is shown only once. Give it a name like "Grok" so you know what to revoke later.

4. Build your connector URL. Replace YOUR_API_KEY with the key you copied.

https://postaxis.io/api/mcp?key=YOUR_API_KEY

5. Add the connector in Grok. Add a new connector (custom MCP server) and paste the full URL. The exact menu name can change between Grok versions; look for connectors or MCP in Grok's settings.

6. Check it works. Start a new chat and ask:

Which social accounts can you post to through PostAxis?

Grok should list your connected accounts by network. That means it reached PostAxis, the key is valid and the tools are available. Now ask for a post.

Treat the URL like a password

Most agents sign in to PostAxis with OAuth: a browser page opens, you approve, the agent gets a token, and your key never exists as text. Grok's connectors only take a URL, so the key travels inside it. That is a normal pattern for URL-only clients, but it changes the rules:

• Anyone with the full URL can post as you. They get the same 11 tools Grok gets, on every account you connected.
• Don't paste it anywhere else. Not in a shared doc, a team chat, a screenshot, a bug report or a support ticket. If you need to show someone the setup, show ?key=YOUR_API_KEY.
• One key per agent. If you also connect another tool with a key, create a separate one. When one leaks, you revoke one key and nothing else breaks.
• Revoke on any doubt. Open Settings → API keys and revoke the key. It stops working immediately. Create a new key and update the connector URL in Grok.
• Revoke when you stop using it. A key for a connector you removed is a key nobody is watching.

4 workflows you can copy

Launch day on X and LinkedIn

The most common job: one announcement, two very different networks.

Our CSV export is live today. Write one line for X (under 200 characters,
no hashtags, link to postaxis.io/changelog at the end) and a short paragraph for
LinkedIn about why customers asked for it. Schedule both for tomorrow at
09:00 America/Chicago.

What Grok does: calls list_accounts to find your X and LinkedIn accounts, get_platform_rules to check the limits, then create_post once, with a separate caption for each account. You get one post ID with two versions, both scheduled for 09:00. PostAxis checks each version against its network's rules before saving.

Fill next week, but show me first

When the calendar is empty and you have one theme, let Grok plan and you approve.

Next week is empty. Plan one post a day, Monday to Friday at 10:00
Europe/Madrid, for X, LinkedIn and Threads, built around our pricing update.
Vary the angle each day. Validate the whole plan and show me the list before
saving anything.

What Grok does: builds the plan and calls create_posts_bulk with validate_only=true. That runs every check and saves nothing, so you get a list plus any problems. Edit in plain language ("Wednesday is too salesy, make it a customer question"), then say "save it" and Grok sends the same call without the flag. A bulk call holds up to 50 posts.

Post an all-clear right now

Some posts cannot wait for a schedule.

The outage is fixed. Post a short all-clear to our Telegram channel and our
Facebook page now: what broke, that it is fixed, and that no data was lost.
Plain tone, no exclamation marks. Confirm when both are live.

What Grok does: create_post with publish now (single posts can go out immediately; bulk calls cannot), then get_post to read the per-network status and confirm both went out. If one network failed, the status says so and you can ask Grok to retry.

Put a photo out tonight

PostAxis does not generate images, so bring your own. Any public image URL works.

Here is today's product shot: https://example.com/shot.jpg
Post it to Instagram and Threads at 18:00 Europe/London. Two-line caption,
no more than three hashtags, and keep the Threads version casual.

What Grok does: upload_media_from_url pulls the image into your PostAxis media library, then create_post attaches it to both accounts with per-network captions. Instagram requires media, so this is the shape every Instagram request should take.

Network limits Grok works within

Video must be MP4 or MOV, 3 to 300 seconds, and one per post. You cannot mix images and video in the same post.

Grok will occasionally write an X post that runs long. PostAxis catches it before saving and returns an error that says what to fix, so a bad post never reaches your calendar. Grok reads the error and tries again.

Tips for better posts

• Give Grok a style note. Use Grok's custom instructions (or paste a short brief at the start of a chat) with your audience, tone, banned words and hashtag rules. It saves you repeating yourself.
• Validate first. For anything beyond one post, ask Grok to validate before saving. It is a free dry run.
• Say the timezone. "09:00 America/Chicago", not "9am". Without one, the agent uses the timezone it was told or UTC.
• Use drafts for anything sensitive. "Save it as a draft" puts the post under Drafts in PostAxis. Read it there and schedule it yourself.
• Name networks explicitly. "Post everywhere" works, but "X and LinkedIn" gets you better, network-specific writing.
• Check the calendar after big batches. Everything Grok creates shows up at app.postaxis.io/calendar, where you can edit or delete it.

Troubleshooting

Is a key in the URL safe? It is as safe as you keep it. Treat the whole URL like a password. If it leaks, revoke the key under Settings → API keys and create a new one.

401 Unauthorized. The key was revoked, mistyped or deleted. Check it is still active under Settings → API keys, and that the URL contains the full key after ?key=.

Grok says no accounts are connected. Connect at least one account under Accounts in PostAxis. With several workspaces, tell Grok which one: "use my Acme workspace".

A post was rejected before saving. PostAxis checks caption length, media count, video length and format first. Ask Grok to read the error and fix it.

Posts are at the wrong time. Say the timezone in the request, then ask Grok to update the scheduled posts.

FAQ

Can Grok post to social media automatically?

Yes. With the PostAxis connector added, Grok can draft, schedule or publish posts to any account you connected in PostAxis, across X, LinkedIn, Threads, Telegram, Facebook Pages, Instagram, TikTok and YouTube Shorts.

Why does Grok need an API key?

Grok's connectors only accept a URL and have no sign-in step, so PostAxis reads the key from the link. Clients that support OAuth, like ChatGPT and Claude, don't need a key.

Is it free?

Every PostAxis plan starts with a 7-day free trial. Because Grok connects with an API key, you also need the API add-on.

Does Grok see my social media passwords?

No. You connect social accounts inside PostAxis. Grok only talks to PostAxis through the key, and the key can be revoked at any time.

Does Grok write a different version for each network?

It can, and it should. Name the networks in one request and Grok sends one post with a version per network. PostAxis rejects any version that breaks that network's limits before it is saved.

Grok handles the words; PostAxis handles the timing, the rules and the publishing. The Grok agent page has the short version of the setup, the MCP reference covers every tool, and the complete guide to AI agents for social media explains OAuth versus API keys in more depth. If you also use other assistants, see the guides for ChatGPT and any MCP client. Start your free trial to try it.