Connect ChatGPT

ChatGPT connects from OpenAI’s cloud, so Postern needs a public HTTPS address on port 443 before you start.

Before you start

• A paid ChatGPT plan that offers Developer mode. It is what lets ChatGPT call a server of your own. Step 3 turns it on.
• A public HTTPS address on port 443, already set up. ChatGPT connects from OpenAI’s cloud on port 443 only. It cannot reach localhost or your private Tailscale network. Nothing on the internet can reach Postern until you set this up, and it is off by default: Set up remote access — Tailscale plus Funnel, about 20 minutes, once.
• Postern running, and the Console at http://localhost:8787. Everything on this side happens at Agents & keys.
• Your password manager open. Postern shows the key once. ChatGPT asks for it at the end of the sign-in, in another window, after step 2 has replaced it on your clipboard.

About 10 minutes, once the address is up. Every ChatGPT label below comes from a real run on 1 August 2026. Where that run recorded no label, this page names none. OpenAI renames these screens, so trust your screen over this page.

If you already saved an agent key that expires, start at step 2.

1. Create a key that expires, and save it

   Open the Console at http://localhost:8787. Go to Agents & keys and press Mint a key.

   In Name, type chatgpt. That name is what the record prints under Who.

   Under Grant which sectors, tick each sector ChatGPT may reach. The six toggles read Finance, Mail, Calendar, Contacts, Health and Home. A grant covers read and act across every provider in the sector, and only Home has anything to act on today — what a grant covers. A key with no sectors ticked still connects, and Postern then denies every read.

   Under Expires, press 30 days, 60 days or 90 days. Do not press Never: the sign-in in step 5 refuses a key that never expires. Once you save an address, the form starts on 90 days and prints This gate is published. A key you paste into a hosted client should expire.

   Postern cannot show you this key again. It keeps a scrambled copy it can check against, never the key itself. The only remedy is a new key. Step 2 then puts your address on the clipboard, over the key, and ChatGPT does not ask for the key until step 5.

   Press Mint the key. A screen opens headed chatgpt is ready, with the key under Agent key — shown once. Press the Copy beside it, then paste and save it in your password manager.

2. Copy the address ChatGPT connects to

   On that same screen, follow Connect a hosted client (claude.ai, ChatGPT) →. From anywhere else: Agents & keys → Set up the bridge →. Both open Connect claude.ai or ChatGPT.

   If your address works for ChatGPT, that page prints it under Paste this into claude.ai or ChatGPT. Press Copy there. It ends in /mcp, which the Console adds itself — the endpoint:

   https://gateway.example-tailnet.ts.net/mcp
   

   The MCP endpoint block on the previous screen prints the address on the machine Postern runs on, which ChatGPT can never reach. It still reads that way after you save a public address. Copy only from Paste this into claude.ai or ChatGPT.

   No Copy button, and the pattern https://your-mac.tailnet.ts.net/mcp in place of your address? One sentence on that page says which of five things is true.

   What the page says	What to do
   Bridge is off — agents can only reach this gate with a pasted key	Nothing was ever published. Set up remote access.
   Bridge is off — an address is saved but not published yet	In the folder that holds docker-compose.yml, run docker compose restart app.
   Bridge is off — this gateway couldn't read its own exposure setting	Open Settings → Remote access, which says why.
   This gateway didn’t answer with its bridge status	About the Console’s own request, not about Postern. Reload.
   Hosted clients egress on port 443 only; on any other port the connection is reset with nothing you'll see.	Your address is local, plain http, or off port 443. Fix it in Settings → Remote access.

3. Turn on Developer mode in ChatGPT

   Open ChatGPT’s settings, then Plugins. Scroll to the bottom of that list, past Browse plugins, and press Developer mode.

   ChatGPT moves you to Security and login, and the address ends #settings/Security?section=developer-mode. The Developer mode row there carries a red ⊘ ELEVATED RISK badge and the line Allows you to add unverified connectors that could modify or erase data permanently. Use at your own risk.

   That badge is correct. Developer mode is what lets ChatGPT call a server you point it at, rather than one OpenAI reviewed. Turn Developer mode on.

   No menu in ChatGPT says Connectors. The settings rail says Plugins, ChatGPT’s banner says Apps, and the addresses still say Connectors. Three names, one thing. Go by the rail.

   The run behind this page met that screen with Developer mode already on. Nobody wrote down the switch’s own name, or what it reads afterwards. Go by the row’s name.

4. Create the plugin and point it at your address

   Open chatgpt.com/plugins. The page carries the heading Plugins — Work with ChatGPT across your favorite tools. Press the + button, top right. The New Plugin form opens.

   • Name — type Postern. Its placeholder reads Custom Tool.
   • Connection — leave the toggle on Server URL, not Tunnel, and paste the address you copied in step 2. Its placeholder reads https://example.com/sse.
   • Authentication — already reads OAuth. Leave it.
   • Icon and Description are optional. Skip both.

   Watch Advanced OAuth settings as you paste. It starts at Enter a valid MCP Server URL to review discovered OAuth settings. Once your address goes in, it changes to Review discovered OAuth settings, or enter them manually, then choose a client setup method and configure default scopes. That change means ChatGPT reached your Postern.

   Under the red ⚠ Custom MCP servers introduce risk warning, tick I understand and want to continue. Create stays greyed out until you do. Press Create.

   The button shows a spinner. ChatGPT then lands on App Preferences, where Permissions reads Allow low-risk. That setting decides when ChatGPT asks you before it uses a plugin, not what Postern allows. The run behind this page changed nothing there. The address still says Connectors, as it does everywhere in ChatGPT’s settings.

   A second tab opens on your own address, served by your own Postern. Step 5 happens in that tab.

   If no tab opens, your browser blocked it. Allow pop-ups for chatgpt.com, then press Create again. You can also close that tab before you approve: press Create again to reopen it.

   If ChatGPT says instead that it could not reach your server, and nothing appears in your logs: nothing arrived, so there was nothing to log. Fix the address in step 2, then wait five minutes before you retry. The Console says the same thing under the address: If claude.ai or ChatGPT says it can't connect, fix the address, wait five minutes, and try once: a hosted client remembers a failed check for a few minutes.

5. Approve the sign-in on your own machine

   Your own Postern serves this tab. It opens blank, then resolves to your own address. It is plain and unstyled, in a system font on a white background — nothing like the Console. That is normal.

   It carries the heading Authorize agent access, then two lines. The first is the name ChatGPT registered with your Postern, followed by is asking to connect to your gateway. The second reads Approving sends a sign-in code to, then the address that code goes to, then . If you did not start this from that app, close this page. Postern prints both from what ChatGPT registered.

   Read both lines before you approve. Anyone who can reach your address can ask to connect, so those two lines are your only check — why the bridge cannot refuse an unknown client. If the name is not the app you started this from, or the address does not belong to OpenAI, close the page.

   Paste the key from step 1 into Paste an agent key from the Console, then press Approve.

   The tab goes black with a spinner and returns to ChatGPT. Postern shows no page of its own to say it worked. ChatGPT confirms instead, with a green message over your plugin’s own page. That page lists no actions yet. That is what a new plugin shows, not a broken connection.

   Your browser’s password manager pops over the key field. Dismiss it. It can cover the Approve button underneath, and the key is not a login.

   The page answers This agent key never expires. Keys used with a cloud client must have an expiry — mint or rotate a key with a 30/90/365-day expiry in the Console, then try again. The key is good; its lifetime is not. Ignore the 365: the Console offers Never, 30 days, 60 days and 90 days, and nothing else.

   Rotate it. Console → Agents & keys → chatgpt → Rotate. The form opens headed Rotate chatgpt. Press 90 days, then Rotate the key, then Copy. Save the new key and run this step again with it. A rotation keeps the name and the sectors, so you do not tick the sectors again.

6. Ask ChatGPT something, then read the record

   In a chat, attach the plugin you named Postern. A [P] Postern chip lands in the message field. Type your question after it.

   ChatGPT shows plain-English progress, never tool names: Describing the Current Context means ChatGPT called describe_context. On the Allow low-risk setting from step 4 it asked no permission per call. A Postern entry in the Sources rail is the sign that a call landed.

   ChatGPT can narrate work it never did. On the 1 August 2026 run it printed a progress line about a weekly total, then Worked for 50s, then: Postern didn’t provide any transaction data in this chat, so I can’t calculate the total without guessing. No call for it reached the record. When an answer looks empty, open Console → The ledger before you change anything.

   That failure also offers the wrong fix: its link points at chatgpt.com/apps, the public directory, where a plugin you made yourself never appears. Yours is on the plugins page, under Personal → Created by me.

Confirm it works

• chatgpt.com/plugins lists Postern under Personal → Created by me.
• Console → The ledger holds a row with chatgpt under Who.
• That row names the tool ChatGPT called under Tool.
• Leave the sector filter alone. The Console says why: One sector at a time also leaves out every call that belonged to no sector — an agent asking what the gate holds, or a handshake the gate refused. Those are still recorded; they just cannot match a sector.
• An empty answer with a row means Postern has no sources yet. No row means nothing arrived.

If something went wrong

What you see	What to do
That agent key was not accepted. Check the key in the Console and try again.	You pasted the address, not the key. Paste the key from your password manager into Paste an agent key from the Console.
This agent key never expires. Keys used with a cloud client must have an expiry	Console → Agents & keys → chatgpt → Rotate → 90 days → Rotate the key → Copy. Approve again with the new key.
ChatGPT could not reach your server, and your logs show nothing	The request never arrived. Fix the address in Settings → Remote access, wait five minutes, try once.
Nothing answers at http://localhost:8787, and Postern runs on another machine	Open the Console over SSH first: Set up remote access.

What you have now

ChatGPT holds a temporary pass issued by your own machine, never the key itself. It sees exactly the sectors you ticked in step 1, and appears in the record under the name you gave it. Its access ends when the key expires — the OAuth bridge, for hosted agents.

Revoke the key and Postern refuses ChatGPT’s next call. Rotate it and its passes die at the same moment — revoking and rotating a key.

Three standing costs come with this.

• The key now lives on OpenAI’s infrastructure and dies on the date you chose. Postern then refuses ChatGPT’s calls, and to replace the key you work this page again from step 1.
• Your address stays reachable from the internet until you turn it off in Settings → Remote access. That is also what turns the sign-in off: Stop publishing and the sign-in disappears — nothing else about this gate changes.
• ChatGPT asked no permission per call on the run behind this page, so the sectors you ticked are its whole boundary for as long as the key lives.

Any wait you feel comes from ChatGPT, not Postern. Postern answers reads from its cache, on your own machine.

Next

ChatGPT can only answer from sources Postern already holds. Pick the one you can finish now.

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