diff --git a/lib/constants.js b/lib/constants.js
new file mode 100644
index 0000000..5389b0e
--- /dev/null
+++ b/lib/constants.js
@@ -0,0 +1,114 @@
+/*
+ * This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/.
+ */
+
+/*
+ * Copyright 2016 Joyent, Inc.
+ */
+
+/*
+ * node-triton constants.
+ *
+ * CLI usage:
+ *      $ node lib/constants.js
+ *      ... emits all the constants as a JSON object ...
+ *      $ node lib/constants.js KEY
+ *      ... emits the value of KEY (in json-y form, i.e. quotes removed from a
+ *      string) ...
+ */
+
+var mod_path = require('path');
+
+
+// ---- determining constants
+
+/*
+ * The `triton` CLI's config dir.
+ *
+ * For *testing* only, we allow override of this dir.
+ */
+var CLI_CONFIG_DIR;
+if (process.env.TRITONTEST_CLI_CONFIG_DIR) {
+    CLI_CONFIG_DIR = process.env.TRITONTEST_CLI_CONFIG_DIR;
+} else if (process.platform === 'win32') {
+    /*
+     * For better or worse we are using APPDATA (i.e. the *Roaming* AppData
+     * dir) over LOCALAPPDATA (non-roaming). The former is meant for "user"
+     * data, the latter for "machine" data.
+     *
+     * TODO: We should likely separate out the *cache* subdir to
+     * machine-specific data dir.
+     */
+    CLI_CONFIG_DIR = mod_path.resolve(process.env.APPDATA, 'Joyent', 'Triton');
+} else {
+    CLI_CONFIG_DIR = mod_path.resolve(process.env.HOME, '.triton');
+}
+
+
+// ---- exports
+
+module.exports = {
+    CLI_CONFIG_DIR: CLI_CONFIG_DIR
+};
+
+
+// ---- mainline
+
+function main(argv) {
+    var assert = require('assert-plus');
+    var dashdash = require('cmdln').dashdash;
+
+    assert.arrayOfString(argv, 'argv');
+
+    var options = [
+        {
+            names: ['help', 'h'],
+            type: 'bool',
+            help: 'Print this help and exit.'
+        }
+    ];
+    var parser = dashdash.createParser({options: options});
+    try {
+        var opts = parser.parse(argv);
+    } catch (e) {
+        console.error('lib/constants.js: error: %s', e.message);
+        process.exit(1);
+    }
+
+    if (opts.help) {
+        console.log([
+            'usage: node .../lib/constants.js [OPTIONS] [KEY]',
+            'options:',
+            parser.help().trimRight()
+        ].join('\n'));
+        process.exit(0);
+    }
+
+    var key;
+    if (opts._args.length === 1) {
+        key = opts._args[0];
+    } else if (opts._args.length === 0) {
+        key = null;
+    } else {
+        console.error('lib/constants.js: error: too many args: %s',
+            opts._args.join(' '));
+        process.exit(1);
+    }
+
+    if (key) {
+        var val = module.exports[key];
+        if (typeof (val) === 'string') {
+            console.log(val);
+        } else {
+            console.log(JSON.stringify(val, null, 4));
+        }
+    } else {
+        console.log(JSON.stringify(module.exports, null, 4));
+    }
+}
+
+if (require.main === module) {
+    main(process.argv);
+}