Comfy-Org/ComfyUI · error · ValueError

Positive prompt is too long: {len(prompt)} characters

Error message

Positive prompt is too long: {len(prompt)} characters

What it means

Raised by validate_prompts when the positive prompt exceeds the model's max_length (typically 2500 chars for Kling models, lower for some). Client-side length check performed before the API call so Kling never sees an oversized prompt.

Source

Thrown at comfy_api_nodes/nodes_kling.py:286

    )


def is_valid_image_response(response: KlingImageGenerationsResponse) -> bool:
    """Verifies that the response contains a task result with at least one image."""
    return (
        response.data is not None
        and response.data.task_result is not None
        and response.data.task_result.images is not None
        and len(response.data.task_result.images) > 0
    )


def validate_prompts(prompt: str, negative_prompt: str, max_length: int) -> bool:
    """Verifies that the positive prompt is not empty and that neither promt is too long."""
    if not prompt:
        raise ValueError("Positive prompt is empty")
    if len(prompt) > max_length:
        raise ValueError(f"Positive prompt is too long: {len(prompt)} characters")
    if negative_prompt and len(negative_prompt) > max_length:
        raise ValueError(
            f"Negative prompt is too long: {len(negative_prompt)} characters"
        )
    return True


def validate_task_creation_response(response) -> None:
    """Validates that the Kling task creation request was successful."""
    if not is_valid_task_creation_response(response):
        error_msg = f"Kling initial request failed. Code: {response.code}, Message: {response.message}, Data: {response.data}"
        logging.error(error_msg)
        raise Exception(error_msg)


def validate_video_result_response(response) -> None:
    """Validates that the Kling task result contains a video."""
    if not is_valid_video_response(response):

View on GitHub (pinned to 1c6d8d45b3)

Solutions

1. Shorten the prompt below the model's character limit (2500 for most Kling video nodes)
2. Move overflow detail into the negative prompt only if that field has room — no, trim both to fit
3. If long context is needed, summarize the prompt with an LLM node before the Kling node
4. Show the character count in the UI/node to catch oversize prompts before running

Example fix

// before
prompt = full_story_text  # 4800 chars

// after
MAX = 2500
prompt = full_story_text[:MAX] if len(full_story_text) > MAX else full_story_text  # or summarize

MAX_PROMPT = 2500

def fits(prompt: str) -> bool:
    return len(prompt) <= MAX_PROMPT

assert fits(prompt), f"prompt is {len(prompt)} chars, max {MAX_PROMPT}"

def prompt_within_limit(prompt: str, max_length: int = 2500) -> bool:
    return isinstance(prompt, str) and 0 < len(prompt) <= max_length

try:
    out = await kling_node(prompt=prompt, ...)
except ValueError as e:
    if "too long" in str(e):
        out = await kling_node(prompt=prompt[:2500], ...)
    else:
        raise

When it happens

Trigger: Feeding a Kling node a prompt longer than the max_length passed to validate_prompts — e.g. pasting an entire story, concatenating many prompt fragments, or LLM-generated mega-prompts.

Common situations: Chained prompt-template nodes accumulating text; copying long descriptions from documents; different Kling models having different limits (check the node's limit).

Related errors

• Positive prompt is empty
• Negative prompt is too long: {len(negative_prompt)} characte
• kling-video-o1 only supports durations of 5 or 10 seconds.
• kling-video-o1 does not support audio generation.
• kling-video-o1 does not support 4k resolution.

AI-assisted analysis of Comfy-Org/ComfyUI@1c6d8d45b3 (2026-08-14). Data as JSON: /api/errors/b0e5bb3c78cb3f25. Report an issue: GitHub.