Midjourney API Quick Start

🎯 Understand the Core Concept

The MidJourney API simulates Discord button interactions. Unlike typical REST APIs, it works as a state machine where each operation returns new buttons for the next step.

The 4 Core APIs

API	Purpose	When to Use
`POST /mj/submit/imagine`	Text-to-image generation	Starting point for all workflows
`GET /mj/task/{id}/fetch`	Query task status & get buttons	After every submit (poll until done)
`POST /mj/submit/action`	Click a button (upscale, vary, zoom, etc.)	When you want to operate on an image
`POST /mj/submit/modal`	Submit additional input	Only when status is `MODAL`

📊 Complete Workflow Diagram

┌─────────────────────────────────────────────────────────────────────────────┐
│                         MIDJOURNEY API WORKFLOW                             │
└─────────────────────────────────────────────────────────────────────────────┘

  ┌──────────────────┐
  │  POST /submit/   │  ← Step 1: Submit prompt, get task_id
  │     imagine      │
  └────────┬─────────┘
           │ Returns: { "result": "task_id_1" }
           ▼
  ┌──────────────────┐
  │ GET /task/{id}/  │  ← Step 2: Poll until status = "SUCCESS"
  │      fetch       │
  └────────┬─────────┘
           │ Returns: imageUrl + buttons[] (U1,U2,U3,U4,V1,V2,V3,V4,🔄)
           ▼
  ┌──────────────────┐
  │  POST /submit/   │  ← Step 3: Click a button using customId
  │     action       │
  └────────┬─────────┘
           │ Returns: { "result": "task_id_2" }
           ▼
  ┌──────────────────┐
  │ GET /task/{id}/  │  ← Step 4: Poll the new task
  │      fetch       │
  └────────┬─────────┘
           │
           ├─── status = "SUCCESS" → Done! Get imageUrl
           │
           └─── status = "MODAL" → Need additional input (see Step 5)
                      │
                      ▼
           ┌──────────────────┐
           │  POST /submit/   │  ← Step 5: Submit mask/prompt for special operations
           │      modal       │
           └────────┬─────────┘
                    │ Returns: { "result": "task_id_3" }
                    ▼
           ┌──────────────────┐
           │ GET /task/{id}/  │  ← Step 6: Poll until SUCCESS
           │      fetch       │
           └──────────────────┘

🔑 Key Concept: Buttons & customId

Every successful task returns a buttons array. Each button has a customId that you use to trigger the next action.

Example response from /mj/task/{id}/fetch:

{
  "status": "SUCCESS",
  "imageUrl": "https://api.cometapi.com/mj/image/xxx",
  "buttons": [
    { "customId": "MJ::JOB::upsample::1::abc123", "label": "U1" },
    { "customId": "MJ::JOB::upsample::2::abc123", "label": "U2" },
    { "customId": "MJ::JOB::variation::1::abc123", "label": "V1" },
    { "customId": "MJ::JOB::reroll::0::abc123", "emoji": "🔄" }
  ]
}

⚠️ Important: customId is NOT a fixed value. It changes for every task. Always get it from the buttons array.

📋 Button Reference by Stage

After IMAGINE (4-grid image)

These buttons are returned when your initial image generation completes:

Button	customId Pattern	Action	Result
U1-U4	`MJ::JOB::upsample::1::xxx`	Upscale single image	High-res single image
V1-V4	`MJ::JOB::variation::1::xxx`	Generate variations	New 4-grid
🔄	`MJ::JOB::reroll::0::xxx::SOLO`	Regenerate all	New 4-grid

After UPSCALE (single image)

After upscaling, you get access to editing tools:

Label	Needs Modal?
Upscale (Subtle) / Upscale (2x)	❌ No
Upscale (Creative) / Upscale (4x)	❌ No
Vary (Subtle) 🪄	❌ No
Vary (Strong) 🪄	❌ No
Vary (Region) 🖌️	✅ Yes (mask)
Zoom Out 2x / 1.5x 🔍	❌ No
Custom Zoom 🔍	✅ Yes (prompt)
⬅️➡️⬆️⬇️ Pan	❌ No
Animate 🎞️	❌ No
🔄 Reroll	❌ No

Note: Button labels and customId formats may vary depending on the MJ version specified in your prompt (e.g., --v 6.1 vs --v 5.2). Always read buttons from the API response.

⚠️ Inpaint (Vary Region) button only appears after Upscale!

⚡ Complete Example: Generate & Upscale

Step 1: Submit Imagine Request

Response:

{ "code": 1, "result": "1768464763141701" }

Step 2: Poll Task Status

Response (when complete):

{
  "status": "SUCCESS",
  "imageUrl": "https://api.cometapi.com/mj/image/1768464763141701",
  "buttons": [
    { "customId": "MJ::JOB::upsample::1::5f20922e-xxx", "label": "U1" },
    { "customId": "MJ::JOB::upsample::2::5f20922e-xxx", "label": "U2" },
    ...
  ]
}

Step 3: Click U1 to Upscale

Response:

{ "code": 1, "result": "1768464800000000" }

Step 4: Poll New Task & Get Result

When you call /mj/submit/action and the task status becomes MODAL instead of SUCCESS, you must call /mj/submit/modal to provide additional input.

Operation	Button	What to Submit
Inpaint	Vary (Region)	`maskBase64` (PNG mask) + `prompt`
Custom Zoom	🔍 Custom Zoom	`prompt` (e.g., "your prompt --zoom 2")

Example: Inpaint Flow

🚀 Speed Mode Selection

Add speed prefix to the path:

Mode	Path Prefix	Example
Fast	`/mj-fast`	`/mj-fast/mj/submit/imagine`
Turbo	`/mj-turbo`	`/mj-turbo/mj/submit/imagine`
Relax	(default)	`/mj/submit/imagine`

🔗 Other Entry Points

These APIs are independent entry points that don't follow the imagine → action flow:

API	Purpose
`POST /mj/submit/blend`	Blend 2-5 images into one
`POST /mj/submit/describe`	Generate prompt from image
`POST /mj/submit/video`	Convert image to video
`POST /mj/submit/edits`	Edit image with mask

❓ Troubleshooting Tips

Based on the API design and workflow, here are common issues you may encounter:

Problem	Likely Cause	Solution
Can't find Vary (Region) button	Looking at 4-grid image	Upscale first (click U1-U4), then check buttons
Task status stuck at `MODAL`	Operation requires additional input	Call `/mj/submit/modal` with required data
`customId` not working	Using outdated or hardcoded value	Always get fresh `customId` from `/mj/task/{id}/fetch` response
Empty `buttons` array	Task still in progress	Wait for `status: "SUCCESS"` before accessing buttons

🎯 Understand the Core Concept#

The 4 Core APIs#

📊 Complete Workflow Diagram#

🔑 Key Concept: Buttons & customId#

📋 Button Reference by Stage#

After IMAGINE (4-grid image)#

After UPSCALE (single image)#

⚡ Complete Example: Generate & Upscale#

Step 1: Submit Imagine Request#

Step 2: Poll Task Status#

Step 3: Click U1 to Upscale#

Step 4: Poll New Task & Get Result#

⚠️ When is Modal Required?#

Confirmed Modal Operations#

🚀 Speed Mode Selection#

🔗 Other Entry Points#

❓ Troubleshooting Tips#