diff --git a/MANIFEST.in b/MANIFEST.in
index 159e4d9ed..9182037f6 100644
--- a/MANIFEST.in
+++ b/MANIFEST.in
@@ -3,3 +3,4 @@ graft artiq/examples
 include artiq/gui/logo*.svg
 include versioneer.py
 include artiq/_version.py
+include artiq/gateware/targets/kasli_generic.schema.json
diff --git a/artiq/frontend/artiq_ddb_template.py b/artiq/frontend/artiq_ddb_template.py
index 15d584fb1..718d50511 100755
--- a/artiq/frontend/artiq_ddb_template.py
+++ b/artiq/frontend/artiq_ddb_template.py
@@ -2,12 +2,12 @@
 
 import argparse
 import sys
-import json
 import textwrap
 from collections import defaultdict
 from itertools import count
 
 from artiq import __version__ as artiq_version
+from artiq.gateware import jsondesc
 
 
 def process_header(output, description):
@@ -57,8 +57,8 @@ def process_header(output, description):
         }}
         """).format(
             variant=description["variant"],
-            core_addr=description.get("core_addr", "192.168.1.70"),
-            ref_period=1/(8*description.get("rtio_frequency", 125e6))),
+            core_addr=description["core_addr"],
+            ref_period=1/(8*description["rtio_frequency"])),
         file=output)
 
 
@@ -116,7 +116,7 @@ class PeripheralManager:
 
     def process_urukul(self, rtio_offset, peripheral):
         urukul_name = self.get_name("urukul")
-        synchronization = peripheral.get("synchronization", False)
+        synchronization = peripheral["synchronization"]
         channel = count(0)
         self.gen("""
             device_db["eeprom_{name}"]={{
@@ -181,10 +181,10 @@ class PeripheralManager:
             }}""",
             name=urukul_name,
             sync_device="\"ttl_{name}_sync\"".format(name=urukul_name) if synchronization else "None",
-            refclk=peripheral.get("refclk", self.master_description.get("rtio_frequency", 125e6)),
+            refclk=peripheral.get("refclk", self.master_description["rtio_frequency"]),
             clk_sel=peripheral["clk_sel"])
-        dds = peripheral.get("dds", "ad9910")
-        pll_vco = peripheral.get("pll_vco", None)
+        dds = peripheral["dds"]
+        pll_vco = peripheral.get("pll_vco")
         for i in range(4):
             if dds == "ad9910":
                 self.gen("""
@@ -280,8 +280,8 @@ class PeripheralManager:
                 }},
             }}""",
             name=mirny_name,
-            refclk=peripheral.get("refclk", 100e6),
-            clk_sel=peripheral.get("clk_sel", 0))
+            refclk=peripheral["refclk"],
+            clk_sel=peripheral["clk_sel"])
 
         return next(channel)
 
@@ -394,7 +394,7 @@ class PeripheralManager:
             }}""",
             sampler_name=sampler_name,
             sampler_channel=rtio_offset+next(channel))
-        pll_vco = peripheral.get("pll_vco", None)
+        pll_vco = peripheral.get("pll_vco")
         for urukul_name in (urukul0_name, urukul1_name):
             self.gen("""
                 device_db["spi_{urukul_name}"] = {{
@@ -425,10 +425,10 @@ class PeripheralManager:
                 }}""",
                 urukul_name=urukul_name,
                 urukul_channel=rtio_offset+next(channel),
-                refclk=peripheral.get("refclk", self.master_description.get("rtio_frequency", 125e6)),
+                refclk=peripheral.get("refclk", self.master_description["rtio_frequency"]),
                 clk_sel=peripheral["clk_sel"],
                 pll_vco=",\n        \"pll_vco\": {}".format(pll_vco) if pll_vco is not None else "",
-                pll_n=peripheral.get("pll_n", 32))
+                pll_n=peripheral["pll_n"])
         return next(channel)
 
     def process_zotino(self, rtio_offset, peripheral):
@@ -573,13 +573,12 @@ def main():
 
     args = parser.parse_args()
 
-    with open(args.master_description, "r") as f:
-        master_description = json.load(f)
+    master_description = jsondesc.load(args.master_description)
 
     satellites = []
-    for destination, description in args.satellite:
-        with open(description, "r") as f:
-            satellites.append((int(destination, 0), json.load(f)))
+    for destination, description_path in args.satellite:
+        satellite_description = jsondesc.load(description_path)
+        satellites.append((int(destination, 0), satellite_description))
 
     if args.output is not None:
         with open(args.output, "w") as f:
diff --git a/artiq/gateware/jsondesc.py b/artiq/gateware/jsondesc.py
new file mode 100644
index 000000000..b936c3a43
--- /dev/null
+++ b/artiq/gateware/jsondesc.py
@@ -0,0 +1,35 @@
+from os import path
+import json
+from jsonschema import Draft7Validator, validators
+
+def extend_with_default(validator_class):
+    validate_properties = validator_class.VALIDATORS["properties"]
+
+    def set_defaults(validator, properties, instance, schema):
+        for property, subschema in properties.items():
+            if "default" in subschema:
+                instance.setdefault(property, subschema["default"])
+
+            for error in validate_properties(
+                validator, properties, instance, schema,
+            ):
+                yield error
+
+    return validators.extend(
+        validator_class, {"properties" : set_defaults},
+    )
+
+schema_path = path.join(path.dirname(__file__), "targets/kasli_generic.schema.json")
+with open(schema_path, "r") as f:
+    schema = json.load(f)
+
+validator = extend_with_default(Draft7Validator)(schema)
+
+def load(description_path):
+    with open(description_path, "r") as f:
+        result = json.load(f)
+
+    global validator
+    validator.validate(result)
+
+    return result
diff --git a/artiq/gateware/targets/kasli_generic.py b/artiq/gateware/targets/kasli_generic.py
index 577b93dad..168b14ee4 100755
--- a/artiq/gateware/targets/kasli_generic.py
+++ b/artiq/gateware/targets/kasli_generic.py
@@ -1,14 +1,12 @@
 #!/usr/bin/env python3
 
 import argparse
-import json
 
 from misoc.integration.builder import builder_args, builder_argdict
 from misoc.targets.kasli import soc_kasli_args, soc_kasli_argdict
 
-from artiq.gateware import rtio
+from artiq.gateware import rtio, eem, jsondesc
 from artiq.gateware.rtio.phy import ttl_simple, ttl_serdes_7series, edge_counter
-from artiq.gateware import eem
 from artiq.gateware.targets.kasli import StandaloneBase, MasterBase, SatelliteBase
 from artiq.build_soc import *
 
@@ -20,7 +18,7 @@ def peripheral_dio(module, peripheral):
     }
     if len(peripheral["ports"]) != 1:
         raise ValueError("wrong number of ports")
-    if peripheral.get("edge_counter", False):
+    if peripheral["edge_counter"]:
         edge_counter_cls = edge_counter.SimpleEdgeCounter
     else:
         edge_counter_cls = None
@@ -37,7 +35,7 @@ def peripheral_urukul(module, peripheral):
         port, port_aux = peripheral["ports"]
     else:
         raise ValueError("wrong number of ports")
-    if peripheral.get("synchronization", False):
+    if peripheral["synchronization"]:
         sync_gen_cls = ttl_simple.ClockGen
     else:
         sync_gen_cls = None
@@ -110,7 +108,7 @@ def peripheral_fastino(module, peripheral):
     if len(peripheral["ports"]) != 1:
         raise ValueError("wrong number of ports")
     eem.Fastino.add_std(module, peripheral["ports"][0],
-        peripheral.get("log2_width", 0))
+        peripheral["log2_width"])
 
 
 def peripheral_phaser(module, peripheral):
@@ -146,7 +144,7 @@ class GenericStandalone(StandaloneBase):
         StandaloneBase.__init__(self, hw_rev=hw_rev, **kwargs)
 
         self.config["SI5324_AS_SYNTHESIZER"] = None
-        self.config["RTIO_FREQUENCY"] = "{:.1f}".format(description.get("rtio_frequency", 125e6)/1e6)
+        self.config["RTIO_FREQUENCY"] = "{:.1f}".format(description["rtio_frequency"]/1e6)
         if "ext_ref_frequency" in description:
             self.config["SI5324_EXT_REF"] = None
             self.config["EXT_REF_FREQUENCY"] = "{:.1f}".format(
@@ -189,8 +187,8 @@ class GenericMaster(MasterBase):
         self.class_name_override = description["variant"]
         MasterBase.__init__(self,
             hw_rev=hw_rev,
-            rtio_clk_freq=description.get("rtio_frequency", 125e6),
-            enable_sata=description.get("enable_sata_drtio", False),
+            rtio_clk_freq=description["rtio_frequency"],
+            enable_sata=description["enable_sata_drtio"],
             **kwargs)
         if "ext_ref_frequency" in description:
             self.config["SI5324_EXT_REF"] = None
@@ -226,8 +224,8 @@ class GenericSatellite(SatelliteBase):
         self.class_name_override = description["variant"]
         SatelliteBase.__init__(self,
                                hw_rev=hw_rev,
-                               rtio_clk_freq=description.get("rtio_frequency", 125e6),
-                               enable_sata=description.get("enable_sata_drtio", False),
+                               rtio_clk_freq=description["rtio_frequency"],
+                               enable_sata=description["enable_sata_drtio"],
                                **kwargs)
         if hw_rev == "v1.0":
             # EEM clock fan-out from Si5324, not MMCX
@@ -263,9 +261,7 @@ def main():
     parser.add_argument("--gateware-identifier-str", default=None,
                         help="Override ROM identifier")
     args = parser.parse_args()
-
-    with open(args.description, "r") as f:
-        description = json.load(f)
+    description = jsondesc.load(args.description)
 
     if description["target"] != "kasli":
         raise ValueError("Description is for a different target")
diff --git a/artiq/gateware/targets/kasli_generic.schema.json b/artiq/gateware/targets/kasli_generic.schema.json
index 0af0441dd..1ea8a6d09 100644
--- a/artiq/gateware/targets/kasli_generic.schema.json
+++ b/artiq/gateware/targets/kasli_generic.schema.json
@@ -42,7 +42,8 @@
         "core_addr": {
             "type": "string",
             "format": "ipv4",
-            "description": "IPv4 address"
+            "description": "IPv4 address",
+            "default": "192.168.1.70"
         },
         "vendor": {
             "type": "string",
@@ -262,7 +263,8 @@
 		            "maximum": 3
 		        },
 		        "pll_n": {
-                            "type": "integer"
+                            "type": "integer",
+                            "default": 32
                         },
 		        "pll_vco": {
                             "type": "integer"