diff --git a/api/onnx_web/chain/blend_img2img.py b/api/onnx_web/chain/blend_img2img.py
index 3bd24933..8a00dfe7 100644
--- a/api/onnx_web/chain/blend_img2img.py
+++ b/api/onnx_web/chain/blend_img2img.py
@@ -27,16 +27,19 @@ def blend_img2img(
     source_image: Image.Image,
     *,
     strength: float,
+    prompt: str = None,
+    **kwargs,
 ) -> Image.Image:
     logger.info('generating image using img2img', params.prompt)
 
     pipe = load_pipeline(OnnxStableDiffusionImg2ImgPipeline,
                             params.model, params.provider, params.scheduler)
 
+    prompt = prompt or params.prompt
     rng = np.random.RandomState(params.seed)
 
     result = pipe(
-        params.prompt,
+        prompt,
         generator=rng,
         guidance_scale=params.cfg,
         image=source_image,
diff --git a/api/onnx_web/chain/blend_inpaint.py b/api/onnx_web/chain/blend_inpaint.py
index bdf42780..5ed461db 100644
--- a/api/onnx_web/chain/blend_inpaint.py
+++ b/api/onnx_web/chain/blend_inpaint.py
@@ -46,6 +46,7 @@ def blend_inpaint(
     fill_color: str = 'white',
     mask_filter: Callable = mask_filter_none,
     noise_source: Callable = noise_source_histogram,
+    **kwargs,
 ) -> Image.Image:
     logger.info('upscaling image by expanding borders', expand)
 
diff --git a/api/onnx_web/chain/correct_gfpgan.py b/api/onnx_web/chain/correct_gfpgan.py
index 3190747c..b24970cb 100644
--- a/api/onnx_web/chain/correct_gfpgan.py
+++ b/api/onnx_web/chain/correct_gfpgan.py
@@ -60,6 +60,7 @@ def correct_gfpgan(
     *,
     upscale: UpscaleParams,
     upsampler: Optional[RealESRGANer] = None,
+    **kwargs,
 ) -> Image.Image:
     if upscale.correction_model is None:
         logger.warn('no face model given, skipping')
diff --git a/api/onnx_web/chain/persist_disk.py b/api/onnx_web/chain/persist_disk.py
index ca877157..6e74429b 100644
--- a/api/onnx_web/chain/persist_disk.py
+++ b/api/onnx_web/chain/persist_disk.py
@@ -21,6 +21,7 @@ def persist_disk(
     source_image: Image.Image,
     *,
     output: str,
+    **kwargs,
 ) -> Image.Image:
     dest = base_join(ctx.output_path, output)
     source_image.save(dest)
diff --git a/api/onnx_web/chain/persist_s3.py b/api/onnx_web/chain/persist_s3.py
index 6698fe11..2653a7f1 100644
--- a/api/onnx_web/chain/persist_s3.py
+++ b/api/onnx_web/chain/persist_s3.py
@@ -26,6 +26,7 @@ def persist_s3(
     bucket: str,
     endpoint_url: str = None,
     profile_name: str = None,
+    **kwargs,
 ) -> Image.Image:
     session = Session(profile_name=profile_name)
     s3 = session.client('s3', endpoint_url=endpoint_url)
diff --git a/api/onnx_web/chain/source_txt2img.py b/api/onnx_web/chain/source_txt2img.py
index 88d49590..4ae06580 100644
--- a/api/onnx_web/chain/source_txt2img.py
+++ b/api/onnx_web/chain/source_txt2img.py
@@ -29,8 +29,11 @@ def source_txt2img(
     source_image: Image.Image,
     *,
     size: Size,
+    prompt: str = None,
+    **kwargs,
 ) -> Image.Image:
-    logger.info('generating image using txt2img, %s steps', params.steps)
+    prompt = prompt or params.prompt
+    logger.info('generating image using txt2img, %s steps: %s', params.steps, prompt)
 
     if source_image is not None:
         logger.warn('a source image was passed to a txt2img stage, but will be discarded')
@@ -42,7 +45,7 @@ def source_txt2img(
     rng = np.random.RandomState(params.seed)
 
     result = pipe(
-        params.prompt,
+        prompt,
         height=size.height,
         width=size.width,
         generator=rng,
diff --git a/api/onnx_web/chain/upscale_outpaint.py b/api/onnx_web/chain/upscale_outpaint.py
index bbb4ae30..f6957aa8 100644
--- a/api/onnx_web/chain/upscale_outpaint.py
+++ b/api/onnx_web/chain/upscale_outpaint.py
@@ -46,6 +46,7 @@ def upscale_outpaint(
     fill_color: str = 'white',
     mask_filter: Callable = mask_filter_none,
     noise_source: Callable = noise_source_histogram,
+    **kwargs,
 ) -> Image.Image:
     logger.info('upscaling image by expanding borders: %s', expand)
 
diff --git a/api/onnx_web/chain/upscale_resrgan.py b/api/onnx_web/chain/upscale_resrgan.py
index 3d83083e..bc9ec56d 100644
--- a/api/onnx_web/chain/upscale_resrgan.py
+++ b/api/onnx_web/chain/upscale_resrgan.py
@@ -77,6 +77,7 @@ def upscale_resrgan(
     source_image: Image.Image,
     *,
     upscale: UpscaleParams,
+    **kwargs,
 ) -> Image.Image:
     logger.info('upscaling image with Real ESRGAN', upscale.scale)
 
diff --git a/api/onnx_web/chain/upscale_stable_diffusion.py b/api/onnx_web/chain/upscale_stable_diffusion.py
index 4543cccd..a189663d 100644
--- a/api/onnx_web/chain/upscale_stable_diffusion.py
+++ b/api/onnx_web/chain/upscale_stable_diffusion.py
@@ -67,6 +67,7 @@ def upscale_stable_diffusion(
     source: Image.Image,
     *,
     upscale: UpscaleParams,
+    **kwargs,
 ) -> Image.Image:
     logger.info('upscaling with Stable Diffusion')
 
diff --git a/api/onnx_web/serve.py b/api/onnx_web/serve.py
index 34833ce4..9fcf414a 100644
--- a/api/onnx_web/serve.py
+++ b/api/onnx_web/serve.py
@@ -18,6 +18,7 @@ from flask_cors import CORS
 from flask_executor import Executor
 from glob import glob
 from io import BytesIO
+from jsonschema import validate
 from logging import getLogger
 from PIL import Image
 from onnxruntime import get_available_providers
@@ -26,10 +27,12 @@ from typing import Tuple
 
 
 from .chain import (
+    blend_img2img,
+    blend_inpaint,
     correct_gfpgan,
-    source_txt2img,
     persist_disk,
     persist_s3,
+    source_txt2img,
     upscale_outpaint,
     upscale_resrgan,
     upscale_stable_diffusion,
@@ -120,10 +123,15 @@ mask_filters = {
     'gaussian-screen': mask_filter_gaussian_screen,
 }
 chain_stages = {
-    'correction-gfpgan': correct_gfpgan,
-    'upscaling-outpaint': upscale_outpaint,
-    'upscaling-resrgan': upscale_resrgan,
-    'upscaling-stable-diffusion': upscale_stable_diffusion,
+    'blend-img2img': blend_img2img,
+    'blend-inpaint': blend_inpaint,
+    'correct-gfpgan': correct_gfpgan,
+    'persist-disk': persist_disk,
+    'persist-s3': persist_s3,
+    'source-txt2img': source_txt2img,
+    'upscale-outpaint': upscale_outpaint,
+    'upscale-resrgan': upscale_resrgan,
+    'upscale-stable-diffusion': upscale_stable_diffusion,
 }
 
 # Available ORT providers
@@ -547,37 +555,38 @@ def upscale():
 
 @app.route('/api/chain', methods=['POST'])
 def chain():
+    data = request.json
+
+    with open('./schema.yaml', 'r') as f:
+        schema = yaml.safe_load(f.read())
+
+    logger.info('validating chain request: %s against %s', data, schema)
+    validate(data, schema)
+
+    # get defaults from the regular parameters
     params, size = pipeline_from_request()
     output = make_output_name('chain', params, size)
 
-    # parse body as json, list of stages
-    example = ChainPipeline(stages=[
-        (source_txt2img, StageParams(), {
-            'size': size,
-        }),
-        (upscale_outpaint, StageParams(), {
-            'expand': Border.even(SizeChart.half),
-        }),
-        (persist_disk, StageParams(tile_size=SizeChart.hd8k), {
-            'output': output,
-        }),
-        (upscale_stable_diffusion, StageParams(tile_size=SizeChart.mini,outscale=4), {
-            'upscale': UpscaleParams('stable-diffusion-x4-upscaler', params.provider, scale=4, outscale=4)
-        }),
-        (persist_disk, StageParams(tile_size=SizeChart.hd8k), {
-            'output': output,
-        }),
-        (persist_s3, StageParams(tile_size=SizeChart.hd8k), {
-            'bucket': 'storage-stable-diffusion',
-            'endpoint_url': 'http://scylla.home.holdmyran.ch:8000',
-            'output': output,
-            'profile_name': 'ceph',
-        }),
-    ])
+    pipeline = ChainPipeline()
+    for stage_data in data.get('stages', []):
+        logger.info('request stage: %s', stage_data)
+
+        callback = chain_stages[stage_data.get('type')]
+        kwargs = stage_data.get('params', {})
+
+        stage = StageParams(
+            stage_data.get('name', callback.__name__),
+            tile_size=int(kwargs.get('tile_size', SizeChart.auto)),
+            outscale=int(kwargs.get('outscale', 1)),
+        )
+        # TODO: create Border from border
+        # TODO: create Upscale from upscale
+        pipeline.append((callback, stage, kwargs))
 
     # build and run chain pipeline
-    executor.submit_stored(output, example, context,
-                           params, Image.new('RGB', (1, 1)))
+    fake_source = Image.new('RGB', (1, 1))
+    executor.submit_stored(output, pipeline, context,
+                           params, fake_source, output=output, size=size)
 
     return jsonify({
         'output': output,
diff --git a/api/requirements.txt b/api/requirements.txt
index e368009b..9b07a6eb 100644
--- a/api/requirements.txt
+++ b/api/requirements.txt
@@ -18,4 +18,5 @@ boto3
 flask
 flask-cors
 flask_executor
+jsonschema
 pyyaml
\ No newline at end of file
diff --git a/api/schema.yaml b/api/schema.yaml
new file mode 100644
index 00000000..4b031b09
--- /dev/null
+++ b/api/schema.yaml
@@ -0,0 +1,69 @@
+$id: https://github.com/ssube/onnx-web/blob/main/api/schema.yaml
+$schema: https://json-schema.org/draft/2020-12/schema
+
+$defs:
+  border_params:
+    type: object
+    properties:
+      bottom:
+        type: number
+      left:
+        type: number
+      right:
+        type: number
+      top:
+        type: number
+
+  image_params:
+    type: object
+    required: [prompt]
+    properties:
+      prompt:
+        type: string
+
+  upscale_params:
+    type: object
+    required: [outscale, scale]
+    properties:
+      outscale:
+        type: number
+      scale:
+        type: number
+
+  request_stage:
+    type: object
+    required: [name, type, params]
+    properties:
+      name:
+        type: string
+      type:
+        type: string
+      params:
+        type: object
+        properties:
+          args:
+            type: object
+            additionalProperties: False
+            patternProperties:
+              "^[-_A-Za-z]+$":
+                oneOf:
+                  - type: number
+                  - type: string
+          border:
+            $ref: "#/$defs/border_params"
+          image:
+            $ref: "#/$defs/image_params"
+          upscale:
+            $ref: "#/$defs/upscale_params"
+
+  request_chain:
+    type: array
+    items:
+      $ref: "#/$defs/request_stage"
+
+type: object
+additionalProperties: False
+required: [stages]
+properties:
+  stages:
+    $ref: "#/$defs/request_chain"
diff --git a/common/pipelines/example.json b/common/pipelines/example.json
new file mode 100644
index 00000000..f7b284ff
--- /dev/null
+++ b/common/pipelines/example.json
@@ -0,0 +1,43 @@
+{
+  "stages": [
+    {
+      "name": "start",
+      "type": "source-txt2img",
+      "params": {
+        "prompt": "a magical wizard"
+      }
+    },
+    {
+      "name": "refine",
+      "type": "blend-img2img",
+      "params": {
+        "prompt": "a magical wizard in a robe fighting a dragon"
+      }
+    },
+    {
+      "name": "upscale",
+      "type": "upscale-stable-diffusion",
+      "params": {
+        "model": "stable-diffusion-x4-upscaler",
+        "prompt": "a magical wizard in a robe fighting a dragon",
+        "scale": 4,
+        "outscale": 4,
+        "tile_size": 128
+      }
+    },
+    {
+      "name": "save-local",
+      "type": "persist-disk",
+      "params": {}
+    },
+    {
+      "name": "save-ceph",
+      "type": "persist-s3",
+      "params": {
+        "bucket": "storage-stable-diffusion",
+        "endpoint_url": "http://scylla.home.holdmyran.ch:8000",
+        "profile_name": "ceph"
+      }
+    }
+  ]
+}
\ No newline at end of file