# Maximum Prompt Length for GPT-Image2: Hard Limits and Validation

> Discover the 10,000 character maximum prompt length for GPT-Image2. Learn hard limits and how to validate your prompts with this essential guide.

- Repository: [苍何/awesome-gpt-image-2](https://github.com/freestylefly/awesome-gpt-image-2)
- Tags: api-reference
- Published: 2026-09-09

---

**The maximum prompt length for GPT-Image2 is strictly capped at 10,000 characters.**

The `freestylefly/awesome-gpt-image-2` repository implements strict prompt validation to prevent oversized payloads from reaching the underlying **APIMart** service. Understanding this limit is essential for developers integrating with the image generation API, as exceeding the threshold triggers immediate request rejection.

## Where the Limit is Defined

The character ceiling is hard-coded at line 5 of [`shared/apimart.js`](https://github.com/freestylefly/awesome-gpt-image-2/blob/main/shared/apimart.js) as the exported constant `APIMART_MAX_PROMPT_LENGTH`. This centralized definition establishes a single source of truth for the APIMart service constraints across the entire codebase.

```javascript
// shared/apimart.js (line 5)
export const APIMART_MAX_PROMPT_LENGTH = 10_000;

```

By referencing this constant rather than scattering magic numbers throughout the application, the repository ensures that validation logic remains synchronized with the external API’s requirements.

## How the Limit is Enforced

Before any image generation request reaches the external API, the `reserveGeneration` function validates the prompt length at line 117 of [`api/generate-image.js`](https://github.com/freestylefly/awesome-gpt-image-2/blob/main/api/generate-image.js). The function checks if the prompt exceeds `APIMART_MAX_PROMPT_LENGTH` and throws an error immediately if the constraint is violated.

```javascript
// api/generate-image.js
import { APIMART_MAX_PROMPT_LENGTH } from '../shared/apimart.js';

export async function reserveGeneration(client, profile, userId, caseId, prompt) {
  if (!prompt || prompt.length > APIMART_MAX_PROMPT_LENGTH || !Number.isFinite(caseId)) {
    throw new Error('Invalid prompt or case ID');
  }
  // Proceed with generation...
}

```

This preemptive validation prevents unnecessary network calls and ensures the APIMart backend never receives malformed requests that would inevitably fail.

## Validating Prompts Client-Side

To avoid runtime errors, implement validation logic that mirrors the server's checks. The following pattern trims whitespace and verifies length constraints before submission:

```javascript
import { APIMART_MAX_PROMPT_LENGTH } from '../shared/apimart.js';

function isPromptValid(prompt) {
  const trimmed = String(prompt || '').trim();
  return trimmed.length > 0 && trimmed.length <= APIMART_MAX_PROMPT_LENGTH;
}

// Usage
const userPrompt = 'Your detailed image description here...';
if (!isPromptValid(userPrompt)) {
  throw new Error(`Prompt must be between 1 and ${APIMART_MAX_PROMPT_LENGTH} characters`);
}

```

## Summary

- The **maximum prompt length for GPT-Image2** is **10,000 characters**, represented as `10_000` in JavaScript numeric literal notation.
- The constant `APIMART_MAX_PROMPT_LENGTH` in [`shared/apimart.js`](https://github.com/freestylefly/awesome-gpt-image-2/blob/main/shared/apimart.js) serves as the authoritative source for this limit.
- The `reserveGeneration` function in [`api/generate-image.js`](https://github.com/freestylefly/awesome-gpt-image-2/blob/main/api/generate-image.js) enforces this constraint before transmitting requests to the APIMart service.
- Client-side validation should check that prompts contain between 1 and 10,000 characters after trimming whitespace.

## Frequently Asked Questions

### What is the maximum prompt length for GPT-Image2?

The maximum prompt length for GPT-Image2 is **10,000 characters**. This hard limit is enforced by the underlying APIMart service and validated in both the client and server code within the `freestylefly/awesome-gpt-image-2` repository.

### Where is the prompt length limit defined in the codebase?

The limit is defined in [`shared/apimart.js`](https://github.com/freestylefly/awesome-gpt-image-2/blob/main/shared/apimart.js) as the exported constant `APIMART_MAX_PROMPT_LENGTH`. This centralized definition allows the value to be imported and reused across validation functions, ensuring consistency between client-side checks and server-side enforcement.

### What happens if I exceed the 10,000 character limit?

If a prompt exceeds 10,000 characters, the `reserveGeneration` function in [`api/generate-image.js`](https://github.com/freestylefly/awesome-gpt-image-2/blob/main/api/generate-image.js) throws an error with the message "Invalid prompt or case ID". The request is rejected before reaching the external APIMart API, preventing unnecessary network overhead and API errors.

### Can I configure or increase the prompt length limit?

No. The 10,000 character maximum is a fixed constraint of the external APIMart service, not a configurable application setting. The `APIMART_MAX_PROMPT_LENGTH` constant reflects this external limitation and should not be modified, as the upstream service will reject payloads exceeding this size regardless of local configuration changes.