diff --git a/Makefile.am b/Makefile.am
index 34f745d0..07cb3677 100644
--- a/Makefile.am
+++ b/Makefile.am
@@ -105,7 +105,8 @@ libutil_la_LIBADD   = $(BOOST_SYSTEM_LIB) $(BOOST_SYSTEM_LIB)
 
 bin_PROGRAMS = 		\
     json-clean		\
-    json-validate
+    json-validate	\
+    json-schema
 
 json_clean_SOURCES    = json/clean.cpp
 json_clean_DEPENDENCIES = $(top_builddir)/.libs/libutil.la
diff --git a/json/schema.cpp b/json/schema.cpp
new file mode 100644
index 00000000..0777ccdb
--- /dev/null
+++ b/json/schema.cpp
@@ -0,0 +1,615 @@
+/*
+ * This file is part of libgim.
+ *
+ * libgim 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, either version 3 of the License, or (at your option) any later
+ * version.
+ * 
+ * libgim 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 libgim.  If not, see <http://www.gnu.org/licenses/>.
+ *
+ * Copyright 2012 Danny Robson <danny@blubinc.net>
+ */
+
+
+#include "../json.hpp"
+
+#include "../maths.hpp"
+
+#include <cmath>
+#include <cstdlib>
+#include <functional>
+#include <iostream>
+#include <map>
+#include <memory>
+#include <regex>
+
+#include <boost/filesystem.hpp>
+
+using namespace std;
+using namespace std::placeholders;
+
+enum {
+    ARG_COMMAND,
+    ARG_SCHEMA,
+    ARG_INPUT,
+
+    NUM_ARGS
+};
+
+
+void
+print_usage (int argc, char **argv) {
+    if (argc <= ARG_COMMAND)
+        abort ();
+
+    std::cerr << "Usage: " << argv[ARG_COMMAND] << " <schema> <input>\n";
+}
+
+
+const char*
+type_to_string (const json::node &node) {
+    if (node.is_array   ()) return "array";
+    if (node.is_boolean ()) return "boolean";
+    if (node.is_null    ()) return "null";
+    if (node.is_number  ()) return "number";
+    if (node.is_object  ()) return "object";
+    if (node.is_string  ()) return "string";
+
+    unreachable ();
+}
+
+
+bool
+is_node_valid (const json::node   &node,
+               const json::object &schema);
+
+
+bool
+is_type_valid (const json::node &node,
+               const json::node &type) {
+    if (type.is_array ()) {
+        return any_of (type.as_array ().begin (),
+                       type.as_array ().end (),
+                       bind (is_type_valid, ref (node), _1));
+    }
+
+    if (!type.is_string ())
+        throw json::schema_error ("schema type requires array, string, or object");
+
+    static const auto ANY_VALIDATOR = [] (const json::node &) { return true; };
+    static const auto INT_VALIDATOR = [] (const json::node &n) {
+        return n.is_number () && is_integer (n.as_number ());
+    };
+
+    static const map<string, function<bool(const json::node&)>> TYPE_VALIDATORS ({
+        { "array",   bind (&json::node::is_array,   _1) },
+        { "boolean", bind (&json::node::is_boolean, _1) },
+        { "null",    bind (&json::node::is_null,    _1) },
+        { "number",  bind (&json::node::is_number,  _1) },
+        { "object",  bind (&json::node::is_object,  _1) },
+        { "string",  bind (&json::node::is_string,  _1) },
+        { "any",     ANY_VALIDATOR },
+        { "integer", INT_VALIDATOR },
+    });
+
+    auto pos = TYPE_VALIDATORS.find (type.as_string ().native ());
+    if (pos == TYPE_VALIDATORS.end ()) {
+        std::cerr << "warning: unknown type " << type.as_string ().native () << ". assuming valid.\n";
+        return true;
+    }
+
+    return pos->second(node);
+}
+
+
+bool
+is_disallow_valid (const json::node &node,
+                   const json::node &constraint)
+    { return !is_type_valid (node, constraint); }
+
+
+bool
+is_enum_valid (const json::node &node,
+               const json::node &constraint) {
+    if (!constraint.is_array ())
+        throw json::schema_error ("enum validation requires an array");
+
+    const json::array &valids = constraint.as_array ();
+    return valids.end () != std::find (valids.begin (),
+                                       valids.end   (),
+                                       node);
+}
+
+
+bool
+is_enum_valid (const json::string &node,
+               const json::node   &constraint) {
+    return is_enum_valid (static_cast<const json::node&> (node), constraint);
+}
+
+
+bool
+is_always_valid (const json::node &,
+                 const json::node &)
+    { return true; }
+
+
+/*static const map<string, validator_t> COMMON_VALIDATORS ({
+    { "description", &is_always_valid   },
+    { "disallow",    &is_disallow_valid },
+    { "enum",        &is_enum_valid     },
+    { "title",       &is_always_valid   },
+    { "type",        &is_type_valid     },
+});*/
+
+
+
+bool
+is_boolean_valid (const json::node   &node,
+                  const json::object &)
+    { return node.is_boolean (); }
+
+
+bool
+is_null_valid (const json::node   &node,
+               const json::object &)
+    { return node.is_null (); }
+
+
+//
+// JSON number
+//
+
+bool
+is_minimum_valid (const json::number &node,
+                  const json::node   &constraint) {
+    return constraint["minimum"].as_number () <= node;
+}
+
+
+bool
+is_maximum_valid (const json::number &node,
+                  const json::node   &constraint) {
+    return constraint["maximum"].as_number () >= node;
+}
+
+
+bool
+is_exclusive_minimum_valid (const json::number &node,
+                            const json::node   &constraint) {
+    return constraint["exclusiveMinimum"].as_number () < node;
+}
+
+
+bool
+is_exclusive_maximum_valid (const json::number &node,
+                            const json::node   &constraint) {
+    return constraint["exclusiveMaximum"].as_number () > node;
+}
+
+
+bool
+is_divisible_by_valid (const json::number &node,
+                       const json::node   &constraint) {
+    return exactly_equal (fmod (node.native (),
+                                constraint["divisibleBy"].as_number ()),
+                          0.0);
+}
+
+
+bool
+is_number_valid (const json::number &node,
+                 const json::object &schema) {
+    typedef bool (*number_validator_t)(const json::number&, const json::node&);
+    static const map<string, number_validator_t> VALIDATORS = {
+        { "minimum",          &is_minimum_valid }, 
+        { "maximum",          &is_maximum_valid }, 
+        { "exclusiveMinimum", &is_exclusive_minimum_valid }, 
+        { "exclusiveMaximum", &is_exclusive_maximum_valid }, 
+        { "divisibleBy",      &is_divisible_by_valid  }, 
+    };
+
+    for (const auto &i: schema) {
+        const std::string &key       = i.first;
+        const auto        &validator = VALIDATORS.find (key);
+        if (validator == VALIDATORS.end ()) {
+            std::cerr << "Unknown validation constraint: " << key << "\n";
+            continue;
+        }
+
+        const json::node &val = *i.second;
+        if (!validator->second (node, schema))
+            return false;
+    }
+
+    return true;
+}
+
+
+bool
+is_number_valid (const json::node   &node,
+                 const json::object &schema) {
+    not_implemented ();
+    return true;
+}
+
+
+//
+// JSON string
+//
+
+
+bool
+is_min_length_valid (const json::string &node,
+                     const json::node   &constraint) {
+    if (!is_integer (constraint))
+        return false;
+
+    return node.size () >= constraint.as_number ();
+}
+
+
+bool
+is_max_length_valid (const json::string &node,
+                     const json::node   &constraint) {
+    if (!is_integer (constraint))
+        return false;
+
+    return node.size () <= constraint.as_number ();
+}
+
+
+bool
+is_pattern_valid (const json::string &node,
+                  const json::node   &constraint) {
+    if (!constraint.is_string ())
+        return false;
+
+    regex pattern (constraint.as_string ().native (),
+                   regex_constants::ECMAScript);
+    return regex_match (node.native (), pattern);
+}
+
+
+bool
+is_string_valid (const json::string &node,
+                 const json::object &schema) {
+    typedef bool (*string_validator_t)(const json::string&, const json::node&);
+    static const map<std::string, string_validator_t> VALIDATORS  = {
+        { "minLength", &is_min_length_valid },
+        { "maxLength", &is_max_length_valid },
+        { "pattern",   &is_pattern_valid },
+        { "enum",      &is_enum_valid },
+    };
+
+    for (const json::object::const_iterator::value_type &i: schema) {
+        const std::string &key        =  i.first;
+        const json::node  &constraint = *i.second;
+
+        auto validator = VALIDATORS.find (key);
+        if (validator == VALIDATORS.end ()) {
+            std::cerr << "Unknown validation constraint: " << key << "\n";
+            continue;
+        }
+
+        if (!validator->second (node, constraint)) {
+            std::cerr << "Failed string constraint: " << key << "\n";
+            return false;
+        }
+    }
+
+    return true;
+}
+
+
+bool
+is_string_valid (const json::node   &node,
+                 const json::object &schema) {
+    if (!node.is_string ())
+        return false;
+    return is_string_valid (node.as_string (), schema);
+}
+
+//
+// JSON array
+//
+
+
+bool
+is_max_items_valid (const json::array &node,
+                    const json::node  &constraint) {
+    if (!constraint.is_number () && is_integer (constraint.as_number ()))
+        throw json::schema_error ("max_items should be an integer");
+
+    return node.size () <= constraint.as_number ();
+}
+
+
+bool
+is_min_items_valid (const json::array &node,
+                    const json::node  &constraint) {
+    if (!constraint.is_number () && is_integer (constraint.as_number ()))
+        throw json::schema_error ("min_items should be an integer");
+
+    return node.size () >= constraint.as_number ();
+}
+
+
+bool
+is_unique_items_valid (const json::array &node,
+                       const json::node  &constraint) {
+    if (!constraint.is_boolean ())
+        throw json::schema_error ("uniqueItems must be a boolean");
+
+    if (node.size () < 2) 
+        return true;
+
+
+    for (json::array::const_iterator i = node.begin (); i != node.end () - 1; ++i) {
+        if (find (i + 1, node.end (), *i) != node.end ())
+            return false;
+    }
+
+    return true;
+}
+
+
+bool
+is_items_valid (const json::array &node,
+                const json::node  &_schema) {
+    if (!_schema.is_object ())
+        throw json::schema_error ("array_items constraint must be an object");
+    const json::object &schema = _schema.as_object ();
+
+    for (const json::node &i: node)
+        if (!is_node_valid (i, schema))
+            return false;
+
+    return true;
+
+    not_implemented ();
+    return false;
+}
+
+
+bool
+is_additional_items_valid (const json::array &node,
+                           const json::node  &constraint) {
+    not_implemented ();
+    return false;
+}
+
+
+bool
+is_array_valid (const json::array  &node,
+                const json::object &schema) {
+    check_hard (node.is_array ());
+
+    typedef bool (*array_validator_t)(const json::array&, const json::node&);
+    static const map<string, array_validator_t> VALIDATORS ({
+        { "items",           &is_items_valid            },
+        { "minItems",        &is_min_items_valid        },
+        { "maxItems",        &is_max_items_valid        },
+        { "uniqueItems",     &is_unique_items_valid     },
+        { "additionalItems", &is_additional_items_valid },
+    });
+
+    for (const json::object::const_iterator::value_type &i: schema) {
+        const std::string &key        = i.first;
+        const json::node  &constraint = *i.second;
+
+        auto validator = VALIDATORS.find (key);
+        if (validator == VALIDATORS.end ()) {
+            std::cerr << "Ignoring unknown contraint key: " << key << "\n";
+            continue;
+        }
+
+        if (!validator->second (node, constraint)) {
+            std::cerr << "Failed validating array constraint: " << key << "\n";
+            return false;
+        }
+    }
+
+    return true;
+}
+
+
+//
+// JSON object
+//
+
+bool
+is_properties_valid (const json::object &node,
+                     const json::object &schema) {
+    for (const json::object::const_iterator::value_type &element: node) {
+        const std::string &key =  element.first;
+        const json::node  &val = *element.second;
+
+        if (!schema.has (key)) {
+            std::cerr << "[warning]  no constraint found for key: " << key << "\n";
+            continue;
+        }
+
+        if (!is_node_valid (val, schema[key].as_object ())) {
+            std::cerr << "failed validation on property: " << key << "\n";
+            return false;
+        }
+    }
+
+    return true;
+}
+
+
+bool
+is_properties_valid (const json::object &node,
+                     const json::node   &constraint) {
+    check (node.is_object ());
+
+    if (!constraint.is_object ())
+        throw json::schema_error ("properties needs an object");
+
+    return is_properties_valid (node, constraint.as_object ());
+}
+
+
+bool
+is_object_valid (const json::object &node,
+                 const json::object &schema) {
+    typedef bool (*object_validator_t)(const json::object&, const json::node&);
+    static const map<string, object_validator_t> VALIDATORS = {
+        { "properties",  &is_properties_valid },
+        //{ "patternProperties", &is_pattern_properties_valid },
+        //{ "additionalProperties", &is_additionaL_properties_valid },
+    };
+
+    for (const json::object::const_iterator::value_type &i: schema) {
+        const std::string &name       =  i.first;
+        const json::node  &constraint = *i.second;
+
+        auto validator = VALIDATORS.find (name);
+        if (validator == VALIDATORS.end ()) {
+            std::cerr << "Unknown constraint name \"" << name << "\". Ignoring.\n";
+            continue;
+        }
+
+        if (!validator->second(node, constraint)) {
+            std::cerr << "Failed validation on: " << name << "\n";
+            return false;
+        }
+    }
+
+    return true;
+}
+
+
+bool
+is_object_valid (const json::node   &node,
+                 const json::object &schema) {
+    if (!node.is_object ())
+        return false;
+
+    return is_object_valid (node.as_object (), schema);
+}
+
+
+//
+// JSON node
+//
+
+bool
+is_node_valid (const json::node   &node,
+               const json::object &schema) {
+    if (schema.has ("$ref")) {
+        const std::string &uri = schema["$ref"].as_string ();
+        std::cerr << "loading referenced schema: " << uri << "\n";
+
+        if (uri[0] == '#') {
+            std::cerr << "[error] schema fragments are not supported\n";
+            return false;
+        }
+
+        auto referenced = json::parse (boost::filesystem::path (uri));
+        return is_node_valid (node, referenced->as_object ());
+    }
+
+    if (schema.has ("type") && 
+       !is_type_valid (node, schema["type"]))
+    {
+        std::cerr << "node type is \"" << type_to_string (node) << "\", expected " << schema["type"] << "\n";
+        return false;
+    }
+
+#define IS_VALID(T)                                             \
+    do {                                                        \
+        if (node.is_##T ()) {                                   \
+            if (!is_##T##_valid (node.as_##T (), schema)) {     \
+                std::cerr << "Failed validation as " #T "\n";   \
+                return false;                                   \
+            }                                                   \
+            return true;                                        \
+        }                                                       \
+    } while (0)
+
+    IS_VALID(array);
+    IS_VALID(boolean);
+    IS_VALID(null);
+    IS_VALID(number);
+    IS_VALID(object);
+    IS_VALID(string);
+
+#undef IS_VALID
+
+    return false;
+    
+
+    /*static const map<string, validator_t> VALIDATORS ({
+        { "description", &is_always_valid   },
+        { "disallow",    &is_disallow_valid },
+        { "enum",        &is_enum_valid     },
+        { "title",       &is_always_valid   },
+        { "type",        &is_type_valid     },
+    });*/
+
+    
+
+    //"required";
+
+    return false;
+}
+
+
+bool
+is_root_valid (const json::node   &node,
+               const json::object &schema) {
+    if (!node.is_array () && !node.is_object ())
+        return false;
+    return is_node_valid (node, schema);
+}
+
+
+//
+// Driver
+//
+
+int
+main (int argc, char **argv) {
+    // Basic argument checking
+    if (argc != NUM_ARGS) {
+        print_usage (argc, argv);
+        return EXIT_FAILURE;
+    }
+    
+    // Load the schema and input
+    unique_ptr<json::node> schema, input;
+    try {
+        schema = json::parse (boost::filesystem::path (argv[ARG_SCHEMA]));
+        input  = json::parse (boost::filesystem::path (argv[ARG_INPUT]));
+    } catch (const json::parse_error &err) {
+        std::cerr << "malformed json for schema or input. " << err.what () << "\n";
+        return EXIT_FAILURE;
+    }
+
+    // Check schema is valid
+    if (!schema->is_object ()) {
+        std::cerr << "Schema should be an object\n";
+        return EXIT_FAILURE;
+    }
+    
+    const json::object &schema_object = schema->as_object ();
+
+    // Check input is valid
+    if (!is_node_valid (*input, schema_object)) {
+        std::cerr << "input does not satisfy the schema\n";
+        return EXIT_FAILURE;
+    }
+
+    return EXIT_SUCCESS;
+}
+