---
title: "Mastodon API: post and schedule from code"
url: "https://get1post.com/developers/mastodon.md"
canonical_url: "https://get1post.com/developers/mastodon"
last_updated: "2026-10-26"
type: "reference"
summary: "Post and schedule to Mastodon with the 1Post API and MCP server: the request, the reply, every rule it is checked against and a dry run."
related: ["https://get1post.com/platforms/mastodon.md", "https://get1post.com/platforms/mastodon/specs.md", "https://get1post.com/docs/api-posts.md", "https://get1post.com/docs/mcp.md"]
---

# Mastodon API: post and schedule from code

Post and schedule to Mastodon with the 1Post API and MCP server: the request, the reply, every rule it is checked against and a dry run.

Post to Mastodon from code with one request: POST /v1/posts with your account id, the text and a schedule_at time. Mastodon text is limited to 500 characters, counted by code points. 1Post allows up to 100 posts a day for each connected account, and a dry run checks a post against every rule first.

## Connect Mastodon first

1. Open Accounts in 1Post and choose Connect, then Mastodon.
2. Enter the address of your instance.
3. Approve access on your instance.
4. Choose the account in the composer.

Then GET /v1/accounts returns the id of the Mastodon account to use in the request.

## Send a post to Mastodon

**Schedule a post**

```bash
curl https://api.get1post.com/v1/posts \
  -H "Authorization: Bearer $ONEPOST_API_KEY" \
  -H "Idempotency-Key: mastodon-first-post" \
  -d '{"accounts":["ACCOUNT_ID"],"text":"A short note on what shipped today.","schedule_at":"2026-11-02T15:00:00Z"}'
```

The reply is 202 with the post (status scheduled) and one destination for Mastodon, which moves from queued to published or failed.

## What you can send to Mastodon

- Text
- Media up to your instance's limits
- Threads
- Polls (not together with media)

## What Mastodon publishes

- On the instance read, a post holds 500 characters and up to 4 attachments, each URL counts 23 characters, and a poll has up to 4 options of 50 characters. Every instance sets its own values.

## Mastodon rules the request is checked against

| Rule | What 1Post checks |
| --- | --- |
| Text limit | 500 characters, counted by code points |
| Media accepted | Images, GIFs, Video |
| Images per post | 4 |
| Videos per post | 1 |
| Images and video together | Not in one post |
| Threads | Yes, as a chain of replies |
| First comment | Yes |
| Polls | 2 to 4 options; not together with media |
| Posts per day, per connected account (1Post) | 100 |

The same table with sources is on the [Mastodon specs page](https://get1post.com/platforms/mastodon/specs.md).

## Mastodon options in the request

- Thread: send parts instead of text. Each part is one post in the chain, up to 100 parts, and each is counted on its own.
- First comment: add first_comment with text to an account object, and delay_min if it should wait.
- Poll: 2 to 4 options, sent in the account's settings.

**A two-part thread in the next free slot**

```json
{
  "accounts": [
    "ACCOUNT_ID"
  ],
  "parts": [
    {
      "text": "1/ The short version."
    },
    {
      "text": "2/ The detail.",
      "delay_min": 1
    }
  ],
  "use_next_free_slot": true
}
```

## Check the post before it is queued

Add "dry_run": true to test a post: nothing is kept, a valid one answers 200 and a broken one answers 422 naming the rule.

**A refused request, abridged**

```json
{
  "error": {
    "code": "invalid_for_platform",
    "message": "mastodon refuses this post: Mastodon counts 532 of 500 characters in part 1. (text_too_long).",
    "fix": "Fix the rule named in the message and send the post again.",
    "retryable": false,
    "request_id": "REQUEST_ID"
  }
}
```

An assistant connected to the [MCP server](https://get1post.com/docs/mcp.md) sends the same fields to create_post; [set one up](https://get1post.com/assistants.md).

## Questions

**Can I post to Mastodon with an API key?**

Yes. A key with write scope can create, change and cancel Mastodon posts for the workspace it belongs to, with the role of the member who made it. See [API authentication](https://get1post.com/docs/api-authentication.md).

**What happens if a Mastodon post breaks a rule?**

The request is refused with invalid_for_platform and the failing rule is named. Fix it and send the request again, or send it with dry_run to test the fix first.

**How many Mastodon posts can I send in a day?**

Up to 100 for each connected account. A request that would pass that answers daily_cap with the time the day frees up.

**My instance allows longer posts. Does 1Post know?**

Yes. Set your instance's limit on the connection and the composer and counters use it instead of 500.

## Sources

- [Mastodon documentation: Instance entity](https://docs.joinmastodon.org/entities/Instance/), read 2026-10-22

## Related

- [Schedule Mastodon posts: formats, limits, setup](https://get1post.com/platforms/mastodon.md)
- [Mastodon specs and limits: text, media, daily cap](https://get1post.com/platforms/mastodon/specs.md)
- [Creating and changing posts with the API: 1Post docs](https://get1post.com/docs/api-posts.md)
- [The MCP server: 1Post docs](https://get1post.com/docs/mcp.md)