AUTOMATIC1111/stable-diffusion-webui · error · HTTPException

Sampler not found

Error message

Sampler not found

What it means

HTTP 400 raised by validate_sampler_name when the sampler_name in an API request has no entry in sd_samplers.all_samplers_map. This map is built from the sampler definitions the running webui knows (euler, dpm++ family, heun, etc., plus any registered by extensions), so an unknown or renamed sampler string is rejected before generation starts.

Source

Thrown at modules/api/api.py:46

from modules.realesrgan_model import get_realesrgan_models
from modules import devices
from typing import Any
import piexif
import piexif.helper
from contextlib import closing
from modules.progress import create_task_id, add_task_to_queue, start_task, finish_task, current_task

def script_name_to_index(name, scripts):
    try:
        return [script.title().lower() for script in scripts].index(name.lower())
    except Exception as e:
        raise HTTPException(status_code=422, detail=f"Script '{name}' not found") from e


def validate_sampler_name(name):
    config = sd_samplers.all_samplers_map.get(name, None)
    if config is None:
        raise HTTPException(status_code=400, detail="Sampler not found")

    return name


def setUpscalers(req: dict):
    reqDict = vars(req)
    reqDict['extras_upscaler_1'] = reqDict.pop('upscaler_1', None)
    reqDict['extras_upscaler_2'] = reqDict.pop('upscaler_2', None)
    return reqDict


def verify_url(url):
    """Returns True if the url refers to a global resource."""

    import socket
    from urllib.parse import urlparse
    try:
        parsed_url = urlparse(url)

View on GitHub (pinned to 82a973c043)

Solutions

1. GET /sdapi/v1/samplers and use one of the returned name values verbatim, splitting scheduler into the separate scheduler field
2. Update the webui so newly supported samplers exist, or install the extension that provides the sampler
3. Use a well-known stable sampler such as 'Euler' or 'DPM++ 2M' plus scheduler 'Karras'

Example fix

# before
json={'prompt':'cat','sampler_name':'DPM++ 2M Karras'}

# after
json={'prompt':'cat','sampler_name':'DPM++ 2M','scheduler':'Karras'}

samplers = requests.get(f'{base}/sdapi/v1/samplers', auth=auth).json()
names = {s['name'] for s in samplers}
if payload['sampler_name'] not in names:
    payload['sampler_name'] = 'Euler'  # or raise
if payload.get('scheduler') and payload['scheduler'].lower() not in {s.lower() for s in {'karras','exponential','sgm_uniform','simple','beta','normal','linear','dddim'}}:
    payload['scheduler'] = None

def sampler_is_valid(name: str, fetched_samplers: list[dict]) -> bool:
    return name in {s['name'] for s in fetched_samplers}

resp = requests.post(txt2img_url, json=payload, auth=auth)
if resp.status_code == 400 and resp.json()['detail'] == 'Sampler not found':
    payload['sampler_name'] = 'DPM++ 2M'; payload['scheduler'] = 'Karras'
    resp = requests.post(txt2img_url, json=payload, auth=auth)

When it happens

Trigger: POST /sdapi/v1/txt2img or /sdapi/v1/img2img with sampler_name like 'dpm++ 2m karras' instead of the split form (sampler_name='DPM++ 2M', scheduler='karras'); using a sampler added by a newer webui or an extension that is not installed; using deprecated sampler_index values that no longer resolve.

Common situations: Clients written against older API versions where combined sampler names were valid; k_diffusion sampler renames between releases (e.g. 'DPM adaptive' vs 'dpmadaptive'); extensions failing to load and thus not registering their samplers; typo or wrong case plus alias mismatch.

Related errors

• Invalid encoded image
• always on script {alwayson_script_name} not found
• Cannot have a selectable script in the always on scripts par
• Init image not found
• Image not found

AI-assisted analysis of AUTOMATIC1111/stable-diffusion-webui@82a973c043 (2026-08-14). Data as JSON: /api/errors/3840c4a8fde52b47. Report an issue: GitHub.