diff --git a/tools/gn/command_args.cc b/tools/gn/command_args.cc
index bb40a6e..237aa0d 100644
--- a/tools/gn/command_args.cc
+++ b/tools/gn/command_args.cc
@@ -12,6 +12,7 @@
 #include "base/command_line.h"
 #include "base/environment.h"
 #include "base/files/file_util.h"
+#include "base/json/json_writer.h"
 #include "base/process/launch.h"
 #include "base/strings/string_number_conversions.h"
 #include "base/strings/string_util.h"
@@ -37,6 +38,7 @@
 const char kSwitchList[] = "list";
 const char kSwitchShort[] = "short";
 const char kSwitchOverridesOnly[] = "overrides-only";
+const char kSwitchJson[] = "json";
 
 bool DoesLineBeginWithComment(const base::StringPiece& line) {
   // Skip whitespace.
@@ -76,14 +78,15 @@
 // Tries to find the comment before the setting of the given value.
 void GetContextForValue(const Value& value,
                         std::string* location_str,
+                        int* line_no,
                         std::string* comment) {
   Location location = value.origin()->GetRange().begin();
   const InputFile* file = location.file();
   if (!file)
     return;
 
-  *location_str = file->name().value() + ":" +
-      base::IntToString(location.line_number());
+  *location_str = file->name().value();
+  *line_no = location.line_number();
 
   const std::string& data = file->contents();
   size_t line_off =
@@ -112,9 +115,11 @@
 void PrintDefaultValueInfo(base::StringPiece name, const Value& value) {
   OutputString(value.ToString(true) + "\n");
   if (value.origin()) {
+    int line_no;
     std::string location, comment;
-    GetContextForValue(value, &location, &comment);
-    OutputString("      From " + location + "\n");
+    GetContextForValue(value, &location, &line_no, &comment);
+    OutputString("      From " + location + ":" + base::IntToString(line_no) +
+                 "\n");
     if (!comment.empty())
       OutputString("\n" + comment);
   } else {
@@ -134,9 +139,11 @@
     OutputString("    Current value = " + val.override_value.ToString(true) +
                  "\n");
     if (val.override_value.origin()) {
+      int line_no;
       std::string location, comment;
-      GetContextForValue(val.override_value, &location, &comment);
-      OutputString("      From " + location + "\n");
+      GetContextForValue(val.override_value, &location, &line_no, &comment);
+      OutputString("      From " + location + ":" + base::IntToString(line_no)
+                   + "\n");
     }
     OutputString("    Overridden from the default = ");
     PrintDefaultValueInfo(name, val.default_value);
@@ -147,6 +154,57 @@
   }
 }
 
+void BuildArgJson(base::Value& dict,
+                  const base::StringPiece& name,
+                  const Args::ValueWithOverride& arg,
+                  bool short_only) {
+  assert(dict.is_dict());
+
+  // Fetch argument name.
+  dict.SetKey("name", base::Value(name));
+
+  // Fetch overridden value inforrmation (if present).
+  if (arg.has_override) {
+    base::DictionaryValue override_dict;
+    override_dict.SetKey("value",
+                         base::Value(arg.override_value.ToString(true)));
+    if (arg.override_value.origin() && !short_only) {
+      int line_no;
+      std::string location, comment;
+      GetContextForValue(arg.override_value, &location, &line_no, &comment);
+      // Omit file and line if set with --args (i.e. no file)
+      if (!location.empty()) {
+        override_dict.SetKey("file", base::Value(location));
+        override_dict.SetKey("line", base::Value(line_no));
+      }
+    }
+    dict.SetKey("current", std::move(override_dict));
+  }
+
+  // Fetch default value information, and comment (if present).
+  base::DictionaryValue default_dict;
+  std::string comment;
+  default_dict.SetKey("value", base::Value(arg.default_value.ToString(true)));
+  if (arg.default_value.origin() && !short_only) {
+    int line_no;
+    std::string location;
+    GetContextForValue(arg.default_value, &location, &line_no, &comment);
+    // Only emit file and line if the value is overridden.
+    if (arg.has_override) {
+      default_dict.SetKey("file", base::Value(location));
+      default_dict.SetKey("line", base::Value(line_no));
+    }
+  }
+  dict.SetKey("default", std::move(default_dict));
+  if (!comment.empty() && !short_only)
+    dict.SetKey("comment", base::Value(comment));
+
+  std::string s;
+  base::JSONWriter::WriteWithOptions(
+      dict, base::JSONWriter::OPTIONS_PRETTY_PRINT, &s);
+  OutputString(s);
+}
+
 int ListArgs(const std::string& build_dir) {
   Setup* setup = new Setup;
   if (!setup->DoSetup(build_dir, false) || !setup->Run())
@@ -175,8 +233,26 @@
   // Cache this to avoid looking it up for each |arg| in the loops below.
   const bool overrides_only =
       base::CommandLine::ForCurrentProcess()->HasSwitch(kSwitchOverridesOnly);
+  const bool short_only =
+      base::CommandLine::ForCurrentProcess()->HasSwitch(kSwitchShort);
 
-  if (base::CommandLine::ForCurrentProcess()->HasSwitch(kSwitchShort)) {
+  if (base::CommandLine::ForCurrentProcess()->HasSwitch(kSwitchJson)) {
+    // Convert all args to JSON, serialize and print them
+    auto list = std::make_unique<base::ListValue>();
+    for (const auto& arg : args) {
+      if (overrides_only && !arg.second.has_override)
+        continue;
+      list->GetList().emplace_back(base::DictionaryValue());
+      BuildArgJson(list->GetList().back(), arg.first, arg.second, short_only);
+    }
+    std::string s;
+    base::JSONWriter::WriteWithOptions(
+        *list.get(), base::JSONWriter::OPTIONS_PRETTY_PRINT, &s);
+    OutputString(s);
+    return 0;
+  }
+
+  if (short_only) {
     // Short <key>=<current_value> output.
     for (const auto& arg : args) {
       if (overrides_only && !arg.second.has_override)
@@ -354,7 +430,7 @@
       Note: you can edit the build args manually by editing the file "args.gn"
       in the build directory and then running "gn gen <out_dir>".
 
-  gn args <out_dir> --list[=<exact_arg>] [--short] [--overrides-only]
+  gn args <out_dir> --list[=<exact_arg>] [--short] [--overrides-only] [--json]
       Lists all build arguments available in the current configuration, or, if
       an exact_arg is specified for the list flag, just that one build
       argument.
@@ -370,6 +446,25 @@
       arguments that have been overridden (i.e. non-default arguments) will
       be printed. Overrides come from the <out_dir>/args.gn file and //.gn
 
+      If --json is specified, the output will be emitted in json format.
+      JSON schema for output:
+      [
+        {
+          "name": variable_name,
+          "current": {
+            "value": overridden_value,
+            "file": file_name,
+            "line": line_no
+          },
+          "default": {
+            "value": default_value,
+            "file": file_name,
+            "line": line_no
+          },
+          "comment": comment_string
+        },
+        ...
+      ]
 
 Examples