diff --git a/buffet/commands/prop_constraints.cc b/buffet/commands/prop_constraints.cc
new file mode 100644
index 0000000..2376588
--- /dev/null
+++ b/buffet/commands/prop_constraints.cc
@@ -0,0 +1,139 @@
+// Copyright 2014 The Chromium OS Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#include "buffet/commands/prop_constraints.h"
+#include "buffet/commands/schema_constants.h"
+#include "buffet/string_utils.h"
+
+namespace buffet {
+
+// Specializations of TypedValueToJson<T>() for supported C++ types.
+std::unique_ptr<base::Value> TypedValueToJson(bool value) {
+  return std::unique_ptr<base::Value>(base::Value::CreateBooleanValue(value));
+}
+std::unique_ptr<base::Value> TypedValueToJson(int value) {
+  return std::unique_ptr<base::Value>(base::Value::CreateIntegerValue(value));
+}
+std::unique_ptr<base::Value> TypedValueToJson(double value) {
+  return std::unique_ptr<base::Value>(base::Value::CreateDoubleValue(value));
+}
+std::unique_ptr<base::Value> TypedValueToJson(const std::string& value) {
+  return std::unique_ptr<base::Value>(base::Value::CreateStringValue(value));
+}
+
+// Constraint ----------------------------------------------------------------
+Constraint::~Constraint() {}
+
+bool Constraint::ReportErrorLessThan(
+    ErrorPtr* error, const std::string& val, const std::string& limit) {
+  Error::AddToPrintf(error, commands::errors::kDomain,
+                     commands::errors::kOutOfRange,
+                     "Value %s is out of range. It must not be less than %s",
+                     val.c_str(), limit.c_str());
+  return false;
+}
+
+bool Constraint::ReportErrorGreaterThan(
+    ErrorPtr* error, const std::string& val, const std::string& limit) {
+  Error::AddToPrintf(error, commands::errors::kDomain,
+                     commands::errors::kOutOfRange,
+                     "Value %s is out of range. It must not be greater than %s",
+                     val.c_str(), limit.c_str());
+  return false;
+}
+
+bool Constraint::ReportErrorNotOneOf(
+    ErrorPtr* error, const std::string& val,
+    const std::vector<std::string>& values) {
+  Error::AddToPrintf(error, commands::errors::kDomain,
+                     commands::errors::kOutOfRange,
+                     "Value %s is invalid. Expected one of [%s]",
+                     val.c_str(), string_utils::Join(',', values).c_str());
+  return false;
+}
+
+bool Constraint::AddToJsonDict(base::DictionaryValue* dict,
+                               bool overridden_only,
+                               ErrorPtr* error) const {
+  if (!overridden_only || HasOverriddenAttributes()) {
+    auto value = ToJson(error);
+    if (!value)
+      return false;
+    dict->SetWithoutPathExpansion(GetDictKey(), value.release());
+  }
+  return true;
+}
+
+// ConstraintStringLength -----------------------------------------------------
+ConstraintStringLength::ConstraintStringLength(
+    const InheritableAttribute<int>& limit) : limit_(limit) {}
+ConstraintStringLength::ConstraintStringLength(int limit) : limit_(limit) {}
+
+bool ConstraintStringLength::HasOverriddenAttributes() const {
+  return !limit_.is_inherited;
+}
+
+std::unique_ptr<base::Value> ConstraintStringLength::ToJson(
+    ErrorPtr* error) const {
+  return TypedValueToJson(limit_.value);
+}
+
+// ConstraintStringLengthMin --------------------------------------------------
+ConstraintStringLengthMin::ConstraintStringLengthMin(
+    const InheritableAttribute<int>& limit) : ConstraintStringLength(limit) {}
+ConstraintStringLengthMin::ConstraintStringLengthMin(int limit)
+    : ConstraintStringLength(limit) {}
+
+bool ConstraintStringLengthMin::Validate(const Any& value,
+                                         ErrorPtr* error) const {
+  std::string str = value.Get<std::string>();
+  int length = static_cast<int>(str.size());
+  if (length < limit_.value) {
+    if (limit_.value == 1) {
+      Error::AddTo(error, commands::errors::kDomain,
+                   commands::errors::kOutOfRange, "String must not be empty");
+    } else {
+      Error::AddToPrintf(error, commands::errors::kDomain,
+                         commands::errors::kOutOfRange,
+                         "String must be at least %d characters long, "
+                         "actual length of string '%s' is %d", limit_.value,
+                         str.c_str(), length);
+    }
+    return false;
+  }
+  return true;
+}
+
+std::shared_ptr<Constraint>
+    ConstraintStringLengthMin::CloneAsInherited() const {
+  return std::make_shared<ConstraintStringLengthMin>(limit_.value);
+}
+
+// ConstraintStringLengthMax --------------------------------------------------
+ConstraintStringLengthMax::ConstraintStringLengthMax(
+    const InheritableAttribute<int>& limit) : ConstraintStringLength(limit) {}
+ConstraintStringLengthMax::ConstraintStringLengthMax(int limit)
+    : ConstraintStringLength(limit) {}
+
+bool ConstraintStringLengthMax::Validate(const Any& value,
+                                         ErrorPtr* error) const {
+  std::string str = value.Get<std::string>();
+  int length = static_cast<int>(str.size());
+  if (length > limit_.value) {
+    Error::AddToPrintf(error, commands::errors::kDomain,
+                       commands::errors::kOutOfRange,
+                       "String must be no more than %d character(s) long, "
+                       "actual length of string '%s' is %d", limit_.value,
+                       str.c_str(), length);
+    return false;
+  }
+  return true;
+}
+
+std::shared_ptr<Constraint>
+    ConstraintStringLengthMax::CloneAsInherited() const {
+  return std::make_shared<ConstraintStringLengthMax>(limit_.value);
+}
+
+}  // namespace buffet