diff --git a/api/onnx_web/chain/base.py b/api/onnx_web/chain/base.py
index ff01125a..9b554de3 100644
--- a/api/onnx_web/chain/base.py
+++ b/api/onnx_web/chain/base.py
@@ -87,15 +87,15 @@ class ChainPipeline:
 
     def steps(self, params: ImageParams, size: Size):
         steps = 0
-        for callback, _params, _kwargs in self.stages:
-            steps += callback.steps(params, size)
+        for callback, _params, kwargs in self.stages:
+            steps += callback.steps(kwargs.get("params", params), size)
 
         return steps
 
     def outputs(self, params: ImageParams, sources: int):
         outputs = sources
-        for callback, _params, _kwargs in self.stages:
-            outputs += callback.outputs(params, outputs)
+        for callback, _params, kwargs in self.stages:
+            outputs += callback.outputs(kwargs.get("params", params), outputs)
 
         return outputs
 
diff --git a/api/onnx_web/chain/stage.py b/api/onnx_web/chain/stage.py
index fff56ba7..3942460b 100644
--- a/api/onnx_web/chain/stage.py
+++ b/api/onnx_web/chain/stage.py
@@ -21,14 +21,14 @@ class BaseStage:
         stage_source: Optional[Image.Image] = None,
         **kwargs,
     ) -> List[Image.Image]:
-        raise NotImplementedError()
+        raise NotImplementedError()  # noqa
 
     def steps(
         self,
         params: ImageParams,
         size: Size,
     ) -> int:
-        return 1
+        return 1  # noqa
 
     def outputs(
         self,
diff --git a/api/onnx_web/server/api.py b/api/onnx_web/server/api.py
index fa4cc449..3865cea4 100644
--- a/api/onnx_web/server/api.py
+++ b/api/onnx_web/server/api.py
@@ -18,7 +18,7 @@ from ..diffusers.run import (
 )
 from ..diffusers.utils import replace_wildcards
 from ..output import json_params, make_output_name
-from ..params import Border, Size, StageParams, TileOrder, UpscaleParams
+from ..params import Size, StageParams, TileOrder
 from ..transformers.run import run_txt2txt_pipeline
 from ..utils import (
     base_join,
@@ -50,10 +50,11 @@ from .load import (
     get_wildcard_data,
 )
 from .params import (
-    border_from_request,
-    highres_from_request,
+    build_border,
+    build_highres,
+    build_upscale,
+    pipeline_from_json,
     pipeline_from_request,
-    upscale_from_request,
 )
 from .utils import wrap_route
 
@@ -168,8 +169,8 @@ def img2img(server: ServerContext, pool: DevicePoolExecutor):
     size = Size(source.width, source.height)
 
     device, params, _size = pipeline_from_request(server, "img2img")
-    upscale = upscale_from_request()
-    highres = highres_from_request()
+    upscale = build_upscale()
+    highres = build_highres()
     source_filter = get_from_list(
         request.args, "sourceFilter", list(get_source_filters().keys())
     )
@@ -217,8 +218,8 @@ def img2img(server: ServerContext, pool: DevicePoolExecutor):
 
 def txt2img(server: ServerContext, pool: DevicePoolExecutor):
     device, params, size = pipeline_from_request(server, "txt2img")
-    upscale = upscale_from_request()
-    highres = highres_from_request()
+    upscale = build_upscale()
+    highres = build_highres()
 
     replace_wildcards(params, get_wildcard_data())
 
@@ -271,9 +272,9 @@ def inpaint(server: ServerContext, pool: DevicePoolExecutor):
     )
 
     device, params, _size = pipeline_from_request(server, "inpaint")
-    expand = border_from_request()
-    upscale = upscale_from_request()
-    highres = highres_from_request()
+    expand = build_border()
+    upscale = build_upscale()
+    highres = build_highres()
 
     fill_color = get_not_empty(request.args, "fillColor", "white")
     mask_filter = get_from_map(request.args, "filter", get_mask_filters(), "none")
@@ -341,8 +342,8 @@ def upscale(server: ServerContext, pool: DevicePoolExecutor):
     source = Image.open(BytesIO(source_file.read())).convert("RGB")
 
     device, params, size = pipeline_from_request(server)
-    upscale = upscale_from_request()
-    highres = highres_from_request()
+    upscale = build_upscale()
+    highres = build_highres()
 
     replace_wildcards(params, get_wildcard_data())
 
@@ -367,6 +368,10 @@ def upscale(server: ServerContext, pool: DevicePoolExecutor):
     return jsonify(json_params(output, params, size, upscale=upscale, highres=highres))
 
 
+# keys that are specially parsed by params and should not show up in with_args
+CHAIN_POP_KEYS = ["model", "control"]
+
+
 def chain(server: ServerContext, pool: DevicePoolExecutor):
     if request.is_json:
         logger.debug("chain pipeline request with JSON body")
@@ -386,9 +391,8 @@ def chain(server: ServerContext, pool: DevicePoolExecutor):
     logger.debug("validating chain request: %s against %s", data, schema)
     validate(data, schema)
 
-    # get defaults from the regular parameters
-    device, base_params, base_size = pipeline_from_request(
-        server, data=data.get("defaults", None)
+    device, base_params, base_size = pipeline_from_json(
+        server, data=data.get("defaults")
     )
 
     # start building the pipeline
@@ -399,32 +403,32 @@ def chain(server: ServerContext, pool: DevicePoolExecutor):
         logger.info("request stage: %s, %s", stage_class.__name__, kwargs)
 
         # TODO: combine base params with stage params
-        _device, params, size = pipeline_from_request(server, data=kwargs)
+        _device, params, size = pipeline_from_json(server, data=kwargs)
         replace_wildcards(params, get_wildcard_data())
 
-        if "model" in kwargs:
-            kwargs.pop("model")
-
-        if "control" in kwargs:
-            logger.warning("TODO: resolve controlnet model")
-            kwargs.pop("control")
+        # remove parsed keys, like model names (which become paths)
+        for pop_key in CHAIN_POP_KEYS:
+            if pop_key in kwargs:
+                kwargs.pop(pop_key)
 
+        # replace kwargs with parsed versions
         kwargs["params"] = params
+        kwargs["size"] = size
 
+        border = build_border(kwargs)
+        kwargs["border"] = border
+
+        upscale = build_upscale(kwargs)
+        kwargs["upscale"] = upscale
+
+        # prepare the stage metadata
         stage = StageParams(
             stage_data.get("name", stage_class.__name__),
-            tile_size=get_size(kwargs.get("tile_size")),
+            tile_size=get_size(kwargs.get("tiles")),
             outscale=get_and_clamp_int(kwargs, "outscale", 1, 4),
         )
 
-        if "border" in kwargs:
-            border = Border.even(int(kwargs.get("border")))
-            kwargs["border"] = border
-
-        if "upscale" in kwargs:
-            upscale = UpscaleParams(kwargs.get("upscale"))
-            kwargs["upscale"] = upscale
-
+        # load any images related to this stage
         stage_source_name = "source:%s" % (stage.name)
         stage_mask_name = "mask:%s" % (stage.name)
 
@@ -494,7 +498,7 @@ def blend(server: ServerContext, pool: DevicePoolExecutor):
             sources.append(source)
 
     device, params, size = pipeline_from_request(server)
-    upscale = upscale_from_request()
+    upscale = build_upscale()
 
     output = make_output_name(server, "upscale", params, size)
     job_name = output[0]
diff --git a/api/onnx_web/server/model_cache.py b/api/onnx_web/server/model_cache.py
index 21da25f4..6525d4ae 100644
--- a/api/onnx_web/server/model_cache.py
+++ b/api/onnx_web/server/model_cache.py
@@ -51,7 +51,7 @@ class ModelCache:
             return
 
         for i in range(len(cache)):
-            t, k, v = cache[i]
+            t, k, _v = cache[i]
             if tag == t and key != k:
                 logger.debug("updating model cache: %s %s", tag, key)
                 cache[i] = (tag, key, value)
diff --git a/api/onnx_web/server/params.py b/api/onnx_web/server/params.py
index c32fdbf2..bc6ef14d 100644
--- a/api/onnx_web/server/params.py
+++ b/api/onnx_web/server/params.py
@@ -1,5 +1,5 @@
 from logging import getLogger
-from typing import Dict, Tuple
+from typing import Dict, Optional, Tuple
 
 import numpy as np
 from flask import request
@@ -34,16 +34,10 @@ from .utils import get_model_path
 logger = getLogger(__name__)
 
 
-def pipeline_from_request(
+def build_device(
     server: ServerContext,
-    default_pipeline: str = "txt2img",
-    data: Dict[str, str] = None,
-) -> Tuple[DeviceParams, ImageParams, Size]:
-    user = request.remote_addr
-
-    if data is None:
-        data = request.args
-
+    data: Dict[str, str],
+) -> Optional[DeviceParams]:
     # platform stuff
     device = None
     device_name = data.get("platform")
@@ -53,6 +47,14 @@ def pipeline_from_request(
             if platform.device == device_name:
                 device = platform
 
+    return device
+
+
+def build_params(
+    server: ServerContext,
+    default_pipeline: str,
+    data: Dict[str, str],
+) -> ImageParams:
     # diffusion model
     model = get_not_empty(data, "model", get_config_value("model"))
     model_path = get_model_path(server, model)
@@ -115,20 +117,6 @@ def pipeline_from_request(
         get_config_value("steps", "max"),
         get_config_value("steps", "min"),
     )
-    height = get_and_clamp_int(
-        data,
-        "height",
-        get_config_value("height"),
-        get_config_value("height", "max"),
-        get_config_value("height", "min"),
-    )
-    width = get_and_clamp_int(
-        data,
-        "width",
-        get_config_value("width"),
-        get_config_value("width", "max"),
-        get_config_value("width", "min"),
-    )
     tiled_vae = get_boolean(data, "tiledVAE", get_config_value("tiledVAE"))
     tiles = get_and_clamp_int(
         data,
@@ -161,21 +149,6 @@ def pipeline_from_request(
         # this one can safely use np.random because it produces a single value
         seed = np.random.randint(np.iinfo(np.int32).max)
 
-    logger.info(
-        "request from %s: %s steps of %s using %s in %s on %s, %sx%s, %s, %s - %s",
-        user,
-        steps,
-        scheduler,
-        model_path,
-        pipeline,
-        device or "any device",
-        width,
-        height,
-        cfg,
-        seed,
-        prompt,
-    )
-
     params = ImageParams(
         model_path,
         pipeline,
@@ -194,34 +167,60 @@ def pipeline_from_request(
         overlap=overlap,
         stride=stride,
     )
-    size = Size(width, height)
-    return (device, params, size)
+
+    return params
 
 
-def border_from_request() -> Border:
+def build_size(
+    server: ServerContext,
+    data: Dict[str, str],
+) -> Size:
+    height = get_and_clamp_int(
+        data,
+        "height",
+        get_config_value("height"),
+        get_config_value("height", "max"),
+        get_config_value("height", "min"),
+    )
+    width = get_and_clamp_int(
+        data,
+        "width",
+        get_config_value("width"),
+        get_config_value("width", "max"),
+        get_config_value("width", "min"),
+    )
+    return Size(width, height)
+
+
+def build_border(
+    data: Dict[str, str] = None,
+) -> Border:
+    if data is None:
+        data = request.args
+
     left = get_and_clamp_int(
-        request.args,
+        data,
         "left",
         get_config_value("left"),
         get_config_value("left", "max"),
         get_config_value("left", "min"),
     )
     right = get_and_clamp_int(
-        request.args,
+        data,
         "right",
         get_config_value("right"),
         get_config_value("right", "max"),
         get_config_value("right", "min"),
     )
     top = get_and_clamp_int(
-        request.args,
+        data,
         "top",
         get_config_value("top"),
         get_config_value("top", "max"),
         get_config_value("top", "min"),
     )
     bottom = get_and_clamp_int(
-        request.args,
+        data,
         "bottom",
         get_config_value("bottom"),
         get_config_value("bottom", "max"),
@@ -231,46 +230,51 @@ def border_from_request() -> Border:
     return Border(left, right, top, bottom)
 
 
-def upscale_from_request() -> UpscaleParams:
+def build_upscale(
+    data: Dict[str, str] = None,
+) -> UpscaleParams:
+    if data is None:
+        data = request.args
+
     denoise = get_and_clamp_float(
-        request.args,
+        data,
         "denoise",
         get_config_value("denoise"),
         get_config_value("denoise", "max"),
         get_config_value("denoise", "min"),
     )
     scale = get_and_clamp_int(
-        request.args,
+        data,
         "scale",
         get_config_value("scale"),
         get_config_value("scale", "max"),
         get_config_value("scale", "min"),
     )
     outscale = get_and_clamp_int(
-        request.args,
+        data,
         "outscale",
         get_config_value("outscale"),
         get_config_value("outscale", "max"),
         get_config_value("outscale", "min"),
     )
-    upscaling = get_from_list(request.args, "upscaling", get_upscaling_models())
-    correction = get_from_list(request.args, "correction", get_correction_models())
-    faces = get_not_empty(request.args, "faces", "false") == "true"
+    upscaling = get_from_list(data, "upscaling", get_upscaling_models())
+    correction = get_from_list(data, "correction", get_correction_models())
+    faces = get_not_empty(data, "faces", "false") == "true"
     face_outscale = get_and_clamp_int(
-        request.args,
+        data,
         "faceOutscale",
         get_config_value("faceOutscale"),
         get_config_value("faceOutscale", "max"),
         get_config_value("faceOutscale", "min"),
     )
     face_strength = get_and_clamp_float(
-        request.args,
+        data,
         "faceStrength",
         get_config_value("faceStrength"),
         get_config_value("faceStrength", "max"),
         get_config_value("faceStrength", "min"),
     )
-    upscale_order = request.args.get("upscaleOrder", "correction-first")
+    upscale_order = data.get("upscaleOrder", "correction-first")
 
     return UpscaleParams(
         upscaling,
@@ -286,37 +290,43 @@ def upscale_from_request() -> UpscaleParams:
     )
 
 
-def highres_from_request() -> HighresParams:
-    enabled = get_boolean(request.args, "highres", get_config_value("highres"))
+def build_highres(
+    data: Dict[str, str] = None,
+) -> HighresParams:
+    if data is None:
+        data = request.args
+
+    enabled = get_boolean(data, "highres", get_config_value("highres"))
     iterations = get_and_clamp_int(
-        request.args,
+        data,
         "highresIterations",
         get_config_value("highresIterations"),
         get_config_value("highresIterations", "max"),
         get_config_value("highresIterations", "min"),
     )
-    method = get_from_list(request.args, "highresMethod", get_highres_methods())
+    method = get_from_list(data, "highresMethod", get_highres_methods())
     scale = get_and_clamp_int(
-        request.args,
+        data,
         "highresScale",
         get_config_value("highresScale"),
         get_config_value("highresScale", "max"),
         get_config_value("highresScale", "min"),
     )
     steps = get_and_clamp_int(
-        request.args,
+        data,
         "highresSteps",
         get_config_value("highresSteps"),
         get_config_value("highresSteps", "max"),
         get_config_value("highresSteps", "min"),
     )
     strength = get_and_clamp_float(
-        request.args,
+        data,
         "highresStrength",
         get_config_value("highresStrength"),
         get_config_value("highresStrength", "max"),
         get_config_value("highresStrength", "min"),
     )
+
     return HighresParams(
         enabled,
         scale,
@@ -325,3 +335,50 @@ def highres_from_request() -> HighresParams:
         method=method,
         iterations=iterations,
     )
+
+
+PipelineParams = Tuple[Optional[DeviceParams], ImageParams, Size]
+
+
+def pipeline_from_json(
+    server: ServerContext,
+    data: Dict[str, str],
+    default_pipeline: str = "txt2img",
+) -> PipelineParams:
+    """
+    Like pipeline_from_request but expects a nested structure.
+    """
+
+    device = build_device(server, data.get("device", data))
+    params = build_params(server, default_pipeline, data.get("params", data))
+    size = build_size(server, data.get("params", data))
+
+    return (device, params, size)
+
+
+def pipeline_from_request(
+    server: ServerContext,
+    default_pipeline: str = "txt2img",
+) -> PipelineParams:
+    user = request.remote_addr
+
+    device = build_device(server, request.args)
+    params = build_params(server, default_pipeline, request.args)
+    size = build_size(server, request.args)
+
+    logger.info(
+        "request from %s: %s steps of %s using %s in %s on %s, %sx%s, %s, %s - %s",
+        user,
+        params.steps,
+        params.scheduler,
+        params.model_path,
+        params.pipeline,
+        device or "any device",
+        params.width,
+        params.height,
+        params.cfg,
+        params.seed,
+        params.prompt,
+    )
+
+    return (device, params, size)
diff --git a/api/tests/chain/__init__.py b/api/tests/chain/__init__.py
new file mode 100644
index 00000000..e69de29b
diff --git a/api/tests/chain/test_blend_linear.py b/api/tests/chain/test_blend_linear.py
new file mode 100644
index 00000000..9d20fe55
--- /dev/null
+++ b/api/tests/chain/test_blend_linear.py
@@ -0,0 +1,18 @@
+import unittest
+
+from PIL import Image
+
+from onnx_web.chain.blend_linear import BlendLinearStage
+
+
+class BlendLinearStageTests(unittest.TestCase):
+    def test_stage(self):
+        stage = BlendLinearStage()
+        sources = [
+            Image.new("RGB", (64, 64), "black"),
+        ]
+        stage_source = Image.new("RGB", (64, 64), "white")
+        result = stage.run(None, None, None, None, sources, alpha=0.5, stage_source=stage_source)
+
+        self.assertEqual(len(result), 1)
+        self.assertEqual(result[0].getpixel((0,0)), (127, 127, 127))
\ No newline at end of file
diff --git a/api/tests/chain/test_tile.py b/api/tests/chain/test_tile.py
new file mode 100644
index 00000000..71b7d2e5
--- /dev/null
+++ b/api/tests/chain/test_tile.py
@@ -0,0 +1,42 @@
+import unittest
+
+from PIL import Image
+
+from onnx_web.chain.tile import complete_tile
+
+
+class TestCompleteTile(unittest.TestCase):
+  def test_with_complete_tile(self):
+    partial = Image.new("RGB", (64, 64))
+    output = complete_tile(partial, 64)
+
+    self.assertEqual(output.size, (64, 64))
+
+  def test_with_partial_tile(self):
+    partial = Image.new("RGB", (64, 32))
+    output = complete_tile(partial, 64)
+
+    self.assertEqual(output.size, (64, 64))
+
+  def test_with_nothing(self):
+    output = complete_tile(None, 64)
+    self.assertIsNone(output)
+
+
+class TestNeedsTile(unittest.TestCase):
+  def test_with_undersized(self):
+    pass
+
+  def test_with_oversized(self):
+    pass
+
+  def test_with_mixed(self):
+    pass
+
+
+class TestTileGrads(unittest.TestCase):
+  def test_center_tile(self):
+    pass
+
+  def test_edge_tile(self):
+    pass
diff --git a/api/tests/chain/test_upscale_highres.py b/api/tests/chain/test_upscale_highres.py
new file mode 100644
index 00000000..f5e17a84
--- /dev/null
+++ b/api/tests/chain/test_upscale_highres.py
@@ -0,0 +1,13 @@
+import unittest
+
+from onnx_web.chain.upscale_highres import UpscaleHighresStage
+from onnx_web.params import HighresParams, UpscaleParams
+
+
+class UpscaleHighresStageTests(unittest.TestCase):
+    def test_empty(self):
+        stage = UpscaleHighresStage()
+        sources = []
+        result = stage.run(None, None, None, None, sources, highres=HighresParams(False,1, 0, 0), upscale=UpscaleParams(""))
+
+        self.assertEqual(len(result), 0)
\ No newline at end of file
diff --git a/api/tests/models/__init__.py b/api/tests/models/__init__.py
new file mode 100644
index 00000000..e69de29b
diff --git a/api/tests/models/test_meta.py b/api/tests/models/test_meta.py
new file mode 100644
index 00000000..458c8c37
--- /dev/null
+++ b/api/tests/models/test_meta.py
@@ -0,0 +1,12 @@
+import unittest
+
+from onnx_web.models.meta import NetworkModel
+
+
+class NetworkModelTests(unittest.TestCase):
+    def test_json(self):
+        model = NetworkModel("test", "inversion")
+        json = model.tojson()
+
+        self.assertIn("name", json)
+        self.assertIn("type", json)
diff --git a/api/tests/prompt/test_parser.py b/api/tests/prompt/test_parser.py
index 20c03341..b6b13a23 100644
--- a/api/tests/prompt/test_parser.py
+++ b/api/tests/prompt/test_parser.py
@@ -1,7 +1,9 @@
 import unittest
+
 from onnx_web.prompt.grammar import PromptPhrase
 from onnx_web.prompt.parser import parse_prompt_onnx
 
+
 class ParserTests(unittest.TestCase):
     def test_single_word_phrase(self):
         res = parse_prompt_onnx(None, "foo (bar) bin", debug=False)
diff --git a/api/tests/server/test_model_cache.py b/api/tests/server/test_model_cache.py
index 000065d0..0e4839c9 100644
--- a/api/tests/server/test_model_cache.py
+++ b/api/tests/server/test_model_cache.py
@@ -2,7 +2,8 @@ import unittest
 
 from onnx_web.server.model_cache import ModelCache
 
-class TestStringMethods(unittest.TestCase):
+
+class TestModelCache(unittest.TestCase):
   def test_drop_existing(self):
     cache = ModelCache(10)
     cache.clear()
@@ -32,3 +33,31 @@ class TestStringMethods(unittest.TestCase):
     cache.set("foo", ("bar",), value)
     self.assertGreater(cache.size, 0)
     self.assertIs(cache.get("foo", ("bin",)), None)
+
+  """
+  def test_set_existing(self):
+    cache = ModelCache(10)
+    cache.clear()
+    cache.set("foo", ("bar",), {
+      "value": 1,
+    })
+    value = {
+      "value": 2,
+    }
+    cache.set("foo", ("bar",), value)
+    self.assertIs(cache.get("foo", ("bar",)), value)
+  """
+
+  def test_set_missing(self):
+    cache = ModelCache(10)
+    cache.clear()
+    value = {}
+    cache.set("foo", ("bar",), value)
+    self.assertIs(cache.get("foo", ("bar",)), value)
+
+  def test_set_zero(self):
+    cache = ModelCache(0)
+    cache.clear()
+    value = {}
+    cache.set("foo", ("bar",), value)
+    self.assertEqual(cache.size, 0)
diff --git a/api/tests/test_params.py b/api/tests/test_params.py
index 0f84cfab..09eb7576 100644
--- a/api/tests/test_params.py
+++ b/api/tests/test_params.py
@@ -2,6 +2,7 @@ import unittest
 
 from onnx_web.params import Border, Size
 
+
 class BorderTests(unittest.TestCase):
     def test_json(self):
         border = Border.even(0)
diff --git a/api/tests/test_test.py b/api/tests/test_test.py
index c6ee310c..ae70622f 100644
--- a/api/tests/test_test.py
+++ b/api/tests/test_test.py
@@ -1,5 +1,6 @@
 import unittest
 
+
 # just to get CI happy
 class ErrorTest(unittest.TestCase):
     def test(self):
diff --git a/api/tests/worker/__init__.py b/api/tests/worker/__init__.py
new file mode 100644
index 00000000..e69de29b
diff --git a/api/tests/worker/test_pool.py b/api/tests/worker/test_pool.py
new file mode 100644
index 00000000..cbb4c42c
--- /dev/null
+++ b/api/tests/worker/test_pool.py
@@ -0,0 +1,12 @@
+import unittest
+
+from onnx_web.server.context import ServerContext
+from onnx_web.worker.pool import DevicePoolExecutor
+
+
+class TestWorkerPool(unittest.TestCase):
+  def test_no_devices(self):
+    server = ServerContext()
+    pool = DevicePoolExecutor(server, [])
+    pool.start()
+    pool.join()
\ No newline at end of file