Comfy-Org/ComfyUI · error · Exception

Field '{field_name} cannot be longer than {max_length} char

Error message

 Field '{field_name} cannot be longer than {max_length} characters; was {len(string)} characters long.

What it means

Raised by validate_string() in comfy_api_nodes/util/validation_utils.py when the string exceeds the node's max_length (checked after whitespace stripping). Providers cap prompt sizes (Heygen 1000/5000, Recraft 1000, Kling 2500, LTX 10000, Meshy 600...), and this guard fails locally instead of after upload. Note the message has cosmetic bugs — a leading space and a missing closing quote after the field name — but it fires correctly.

Source

Thrown at comfy_api_nodes/util/validation_utils.py:190

def validate_string(
    string: str,
    strip_whitespace=True,
    field_name="prompt",
    min_length=None,
    max_length=None,
):
    if string is None:
        raise Exception(f"Field '{field_name}' cannot be empty.")
    if strip_whitespace:
        string = string.strip()
    if min_length and len(string) < min_length:
        raise Exception(
            f"Field '{field_name}' cannot be shorter than {min_length} characters; was {len(string)} characters long."
        )
    if max_length and len(string) > max_length:
        raise Exception(
            f" Field '{field_name} cannot be longer than {max_length} characters; was {len(string)} characters long."
        )


def validate_container_format_is_mp4(video: Input.Video) -> None:
    """Validates video container format is MP4."""
    container_format = video.get_container_format()
    if container_format not in ["mp4", "mov,mp4,m4a,3gp,3g2,mj2"]:
        raise ValueError(f"Only MP4 container format supported. Got: {container_format}")


def _ratio_from_tuple(r: tuple[float, float]) -> float:
    a, b = r
    if a <= 0 or b <= 0:
        raise ValueError(f"Ratios must be positive, got {a}:{b}.")
    return a / b

View on GitHub (pinned to 1c6d8d45b3)

Solutions

1. Shorten the prompt below the node's documented limit (see the node tooltip or provider API docs).
2. If you need long context, switch to a provider node with a larger cap (e.g. text/LLM nodes) or summarize first with a local LLM node.
3. Strip ComfyUI-specific syntax (weights, LoRA tags) that the target API ignores and that inflate length.
4. When concatenating template segments, count characters before the API node and truncate deterministically.

Example fix

# before
validate_string(long_script, field_name='prompt', min_length=1, max_length=1000)
# Exception when len(long_script) > 1000

# after
validate_string(long_script[:1000], field_name='prompt', min_length=1, max_length=1000)

MAX = 1000  # per node/provider
if len(text) > MAX:
    text = text[:MAX]

try: validate_string(prompt, max_length=MAX) except Exception as e: raise UserVisibleError(str(e)) from e

When it happens

Trigger: Passing a long prompt to any node calling validate_string(prompt, max_length=N): a 1500-char prompt into Recraft (max 1000), a 4000-char Heygen script into a 1000-char field, or a huge pasted document into a Kling text box (2500).

Common situations: Users paste whole scripts/articles as prompts; prompt-template chains concatenate context until the string overruns; or a workflow tuned for one provider (LTX 10000) is reused with a stricter one (Meshy 600). Also triggered by LoRA-style prompt dumps including weighting syntax that the target API does not use anyway.

Related errors

• Field '{field_name}' cannot be shorter than {min_length} cha
• The prompt references @Audio{max_tag}, but reference mode is
• Field '{field_name}' cannot be empty.
• Connect at least one keyframe image.
• Spreading {len(images)} images across the clip needs an expl

AI-assisted analysis of Comfy-Org/ComfyUI@1c6d8d45b3 (2026-08-14). Data as JSON: /api/errors/3184bc85784b2b1a. Report an issue: GitHub.