diff --git a/docs/changelog.rst b/docs/changelog.rst
index a5976fa..b7cebad 100644
--- a/docs/changelog.rst
+++ b/docs/changelog.rst
@@ -15,6 +15,7 @@ Changelog
    applied. Uninstalling from the same panel removes the PAS plugin
    and the per-user JWT signing secrets.
 
+- #105 Assemble worksheets (layout + QC analyses) through the API
 - #104 Fix Analyses field ignoring a plain list of analysis service UIDs
 - #103 Allow updating the setup configuration objects
 - #102 Support DX Duration (Timedelta) fields via a field manager
diff --git a/src/senaite/jsonapi/api/mutation.py b/src/senaite/jsonapi/api/mutation.py
index 9dc7144..d17f6eb 100644
--- a/src/senaite/jsonapi/api/mutation.py
+++ b/src/senaite/jsonapi/api/mutation.py
@@ -325,9 +325,15 @@ def update_object_with_data(content, record):
                 continue
             logger.debug("update_object_with_data::field %r updated", k)
 
-    invalid = bika_api.validate(content)
-    if invalid:
-        raise BadRequestError(u.to_json(invalid))
+        # Validate the whole object only for the field-manager path, where
+        # the payload maps directly to schema fields. A custom IUpdate
+        # adapter assembles the object through domain operations (e.g. a
+        # worksheet's addAnalyses populates system-managed fields such as
+        # the layout that the generic schema validator cannot check) and
+        # is responsible for its own validity.
+        invalid = bika_api.validate(content)
+        if invalid:
+            raise BadRequestError(u.to_json(invalid))
 
     if record.get("transition", None):
         t = record.get("transition")
diff --git a/src/senaite/jsonapi/configure.zcml b/src/senaite/jsonapi/configure.zcml
index cd6046e..d523003 100644
--- a/src/senaite/jsonapi/configure.zcml
+++ b/src/senaite/jsonapi/configure.zcml
@@ -141,6 +141,19 @@
       factory=".datamanagers.DexterityDataManager"
       />
 
+  <!-- UPDATE HANDLERS
+       Custom create/update handling for types that cannot be assembled
+       through plain field setting.
+  -->
+
+  <!-- Assemble Worksheets through their add methods (builds the layout
+       and supports QC reference/duplicate analyses) -->
+  <adapter
+      for="senaite.core.interfaces.IWorksheet"
+      provides=".interfaces.IUpdate"
+      factory=".update.WorksheetUpdate"
+      />
+
 
   <!-- AT FIELD MANAGERS
        Field level interface to get and set values and get a JSON compatible
diff --git a/src/senaite/jsonapi/update.py b/src/senaite/jsonapi/update.py
new file mode 100644
index 0000000..4fcc2c0
--- /dev/null
+++ b/src/senaite/jsonapi/update.py
@@ -0,0 +1,170 @@
+# -*- coding: utf-8 -*-
+#
+# This file is part of SENAITE.JSONAPI.
+#
+# SENAITE.JSONAPI is free software: you can redistribute it and/or modify it under
+# the terms of the GNU General Public License as published by the Free Software
+# Foundation, version 2.
+#
+# This program is distributed in the hope that it will be useful, but WITHOUT
+# ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS
+# FOR A PARTICULAR PURPOSE. See the GNU General Public License for more
+# details.
+#
+# You should have received a copy of the GNU General Public License along with
+# this program; if not, write to the Free Software Foundation, Inc., 51
+# Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
+#
+# Copyright 2017-2025 by it's authors.
+# Some rights reserved, see README and LICENSE.
+
+from AccessControl import Unauthorized
+from senaite.jsonapi import api
+from senaite.jsonapi import logger
+from senaite.jsonapi.exceptions import BadRequestError
+from senaite.jsonapi.exceptions import ForbiddenError
+from senaite.jsonapi.interfaces import IDataManager
+from senaite.jsonapi.interfaces import IUpdate
+from zope import interface
+
+# Keys consumed by the worksheet assembly instead of the generic
+# fieldmanager path. "Analyses" is accepted as an alias of "analyses".
+WS_ANALYSES = "analyses"
+WS_ANALYSES_ALIAS = "Analyses"
+WS_REFERENCE = "reference_analyses"
+WS_DUPLICATE = "duplicate_analyses"
+
+# Keys never routed through the data manager on update.
+SKIP_FIELDS = ("id", "transition")
+
+
+def extract_uid(value):
+    """Return the UID of a value that is either a UID string or a mapping
+    carrying a `uid` key, else None.
+    """
+    if isinstance(value, dict):
+        return value.get("uid")
+    if api.is_uid(value):
+        return value
+    return None
+
+
+class WorksheetUpdate(object):
+    """IUpdate adapter that assembles a Worksheet through its own add
+    methods.
+
+    Setting the `analyses` field directly only writes the back reference;
+    the worksheet `Layout` (what the results view renders) stays empty.
+    This adapter routes routine analyses through `Worksheet.addAnalyses`
+    so a slot layout is built, and exposes the QC add methods (reference
+    and duplicate analyses) that are otherwise unreachable through the
+    API.
+
+    Recognised keys (all optional):
+
+    - `analyses`: list of routine analysis UIDs (or `{"uid": ...}`)
+    - `reference_analyses`: list of
+      `{"reference_uid": <ReferenceSample>, "services": [<uid>, ...],
+        "slot": <int>}`
+    - `duplicate_analyses`: list of
+      `{"src_slot": <int>, "dest_slot": <int>}`
+
+    Every other key is applied through the regular field managers. The
+    caller (`update_object_with_data`) validates, fires any `transition`
+    and reindexes after this adapter returns.
+    """
+    interface.implements(IUpdate)
+
+    def __init__(self, context):
+        self.context = context
+
+    def is_update_allowed(self):
+        """Worksheets are assembled through this adapter."""
+        return True
+
+    def update_object(self, **data):
+        """Apply plain fields, then assemble routine and QC analyses."""
+        analyses = data.pop(WS_ANALYSES, None)
+        if analyses is None:
+            analyses = data.pop(WS_ANALYSES_ALIAS, None)
+        references = data.pop(WS_REFERENCE, None)
+        duplicates = data.pop(WS_DUPLICATE, None)
+
+        self.set_fields(data)
+        self.add_analyses(analyses)
+        self.add_reference_analyses(references)
+        self.add_duplicate_analyses(duplicates)
+        return self.context
+
+    def set_fields(self, data):
+        """Apply the non-assembly fields through the data manager."""
+        dm = IDataManager(self.context)
+        for name, value in data.items():
+            if name in SKIP_FIELDS:
+                continue
+            try:
+                success = dm.set(name, value, **data)
+            except Unauthorized:
+                raise ForbiddenError(
+                    "Not allowed to set the field '%s'" % name)
+            except ValueError as exc:
+                raise BadRequestError(str(exc))
+            if success is False:
+                logger.warn("WorksheetUpdate::skipping key=%r", name)
+
+    def add_analyses(self, analyses):
+        """Route routine analyses through Worksheet.addAnalyses."""
+        objects = self.resolve_objects(analyses)
+        if objects:
+            self.context.addAnalyses(objects)
+
+    def add_reference_analyses(self, records):
+        """Create QC reference analyses from reference samples."""
+        for record in records or []:
+            reference = self.get_object(record.get("reference_uid"))
+            service_uids = record.get("services") or []
+            slot = to_slot(record.get("slot"))
+            if reference is None or not service_uids:
+                logger.warn(
+                    "Skipping reference analyses record %r", record)
+                continue
+            self.context.addReferenceAnalyses(reference, service_uids, slot)
+
+    def add_duplicate_analyses(self, records):
+        """Create QC duplicate analyses from a source slot."""
+        for record in records or []:
+            src_slot = record.get("src_slot")
+            if src_slot is None:
+                logger.warn(
+                    "Skipping duplicate analyses record %r", record)
+                continue
+            dest_slot = to_slot(record.get("dest_slot"))
+            self.context.addDuplicateAnalyses(to_slot(src_slot), dest_slot)
+
+    def resolve_objects(self, values):
+        """Resolve a list of UID/`{uid}` values to objects."""
+        if not values:
+            return []
+        if not isinstance(values, (list, tuple)):
+            values = [values]
+        objects = []
+        for item in values:
+            obj = self.get_object(extract_uid(item))
+            if obj is None:
+                logger.warn("Skipping unresolvable analysis %r", item)
+                continue
+            objects.append(obj)
+        return objects
+
+    def get_object(self, uid):
+        if not uid:
+            return None
+        return api.get_object_by_uid(uid, None)
+
+
+def to_slot(value):
+    """Coerce a slot value to a non-negative int (0 = auto)."""
+    try:
+        return max(0, int(value))
+    except (TypeError, ValueError):
+        return 0