Use the API from a ChatGPT custom GPT

A custom GPT can call the Ur Next Door API through Actions. ChatGPT reads the API's OpenAPI document, learns every endpoint, and sends your key with each call. You need a ChatGPT plan that lets you create GPTs.

Step 1: Create a key for the GPT

In Settings > API keys on urnextdoor.com, create a key named ChatGPT GPT with the scopes content and read (add schedule to manage scheduled items). media is of limited use in a GPT; see the image section below. Pick a 30 or 90 day expiry. See Create an API key.

Step 2: Create the GPT

1. In ChatGPT, open GPTs and choose Create.
2. Switch to the Configure tab.
3. Give it a name, for example My Ur Next Door publisher.
4. In Instructions, paste the system prompt, and replace its "MY KEY" section with: The API key is configured in this GPT's Action. Never ask me for it and never mention it.

Step 3: Add the Action

1. At the bottom of Configure, choose Create new action.

2. Choose Import from URL and enter:

   Text

   https://urnextdoor.com/api/v1/openapi.json

   ChatGPT loads the schema and lists the operations (getMe, createPost, uploadMedia and the rest). The document is public, so no key is needed to import it.

3. Under Authentication, choose API Key, paste your key, and set Auth Type to Bearer. Save.

4. If ChatGPT asks for a privacy policy URL, use https://urnextdoor.com/privacy.

Step 4: Keep it private and save

Choose Create (or Update) and, when asked who can access it, choose Only me.

Step 5: Test it

In the preview pane, try:

Who am I on Ur Next Door? Use getMe and tell me my plan and the key's scopes.

ChatGPT asks you to allow the call the first time. Then try a real post:

Draft a short post about three ways to save water at home, with the tags water and home.
Show me the draft, and publish it with createPost only after I say yes.

ChatGPT asks for confirmation before actions that change data, such as creating a post. Read what it is about to send before you allow it. The request it makes is equivalent to:

curl -X POST "https://urnextdoor.com/api/v1/posts" \
  -H "Authorization: Bearer $UND_API_KEY" \
  -H "Content-Type: application/json" \
  -H "Idempotency-Key: $(uuidgen)" \
  -d '{
  "title": "Five easy ways to save water at home",
  "body": "<p>Small habits add up. These five saved our building a lot of water this summer.</p><ul><li>Fix dripping taps the same week.</li><li>Run the washing machine only when it is full.</li></ul>",
  "tags": [
    "water",
    "home"
  ]
}'

const res = await fetch("https://urnextdoor.com/api/v1/posts", {
  method: "POST",
  headers: {
    Authorization: `Bearer ${process.env.UND_API_KEY}`,
    "Content-Type": "application/json",
    "Idempotency-Key": crypto.randomUUID(),
  },
  body: JSON.stringify({
    title: "Five easy ways to save water at home",
    body: "<p>Small habits add up. These five saved our building a lot of water this summer.</p><ul><li>Fix dripping taps the same week.</li><li>Run the washing machine only when it is full.</li></ul>",
    tags: ["water", "home"],
  }),
});
console.log(res.status, await res.json());

import os
import uuid

import requests

api_key = os.environ["UND_API_KEY"]

response = requests.post(
    "https://urnextdoor.com/api/v1/posts",
    headers={
        "Authorization": f"Bearer {api_key}",
        "Idempotency-Key": str(uuid.uuid4()),
    },
    json={
        "title": "Five easy ways to save water at home",
        "body": "<p>Small habits add up. These five saved our building a lot of water this summer.</p><ul><li>Fix dripping taps the same week.</li><li>Run the washing machine only when it is full.</li></ul>",
        "tags": ["water", "home"],
    },
    timeout=30,
)
print(response.status_code, response.json())

<?php
$apiKey = getenv('UND_API_KEY');

$payload = [
    'title' => 'Five easy ways to save water at home',
    'body' => '<p>Small habits add up. These five saved our building a lot of water this summer.</p><ul><li>Fix dripping taps the same week.</li><li>Run the washing machine only when it is full.</li></ul>',
    'tags' => ['water', 'home'],
];

$ch = curl_init('https://urnextdoor.com/api/v1/posts');
curl_setopt_array($ch, [
    CURLOPT_CUSTOMREQUEST => 'POST',
    CURLOPT_RETURNTRANSFER => true,
    CURLOPT_HTTPHEADER => [
        'Authorization: Bearer ' . $apiKey,
        'Content-Type: application/json',
        'Idempotency-Key: ' . bin2hex(random_bytes(16)),
    ],
    CURLOPT_POSTFIELDS => json_encode($payload),
]);
$body = curl_exec($ch);
$status = curl_getinfo($ch, CURLINFO_RESPONSE_CODE);

echo $status, PHP_EOL, $body, PHP_EOL;

Sample response: 201 Created

{
  "ok": true,
  "id": 41,
  "slug": "five-easy-ways-to-save-water-at-home",
  "url": "/posts/five-easy-ways-to-save-water-at-home",
  "web_url": "https://urnextdoor.com/posts/five-easy-ways-to-save-water-at-home",
  "item": {
    "id": 41,
    "type": "post",
    "slug": "five-easy-ways-to-save-water-at-home"
  },
  "request_id": "9f8e7d6c5b4a3921"
}

Images in a GPT

GPT Actions are text only, and ChatGPT caps a single request at about 100,000 characters. A base64 image is about a third bigger than the file, so base64 upload through uploadMedia only works for small images, roughly 70 KB or less.

ChatGPT passes files it holds (images you upload or it generates) to Actions as download links in its own openaiFileIdRefs format, which the Ur Next Door API does not read today. Importing files that ChatGPT holds is on the roadmap.

What works today:

• Pass an https:// image URL as featured_image or in gallery. The image is linked, not copied.
• For generated or large images, use Claude Code or Codex CLI, which can upload files from your computer.

Limits to know

• An Action call times out after about 45 seconds, and ChatGPT backs off after repeated 429 or 500 answers.
• Your daily quotas apply to the GPT like any other tool.
• A GPT may not send an Idempotency-Key with every call, so if a create seems to fail, check your profile (or GET /api/v1/scheduled for scheduled items) before asking it to try again.

Frequently asked questions

Next steps

• System prompt for the GPT's instructions.
• Keep your API key safe.
• Prompt recipes.