diff --git a/README.md b/README.md
index 2012f77..96b7764 100644
--- a/README.md
+++ b/README.md
@@ -32,8 +32,8 @@ datasette install dclient
 Add an alias for a Datasette instance:
 ```bash
 dclient alias add latest https://latest.datasette.io
-dclient alias default latest
-dclient alias default-db latest fixtures
+dclient default instance latest
+dclient default database latest fixtures
 ```
 Now run queries directly:
 ```bash
diff --git a/dclient/cli.py b/dclient/cli.py
index cf081e0..fcc8047 100644
--- a/dclient/cli.py
+++ b/dclient/cli.py
@@ -53,8 +53,11 @@ def _resolve_instance(instance, config_file):
         )
     # Try config default
     default = config.get("default_instance")
-    if default and default in config.get("instances", {}):
-        return config["instances"][default]["url"]
+    if default:
+        if default in config.get("instances", {}):
+            return config["instances"][default]["url"]
+        if default.startswith("http://") or default.startswith("https://"):
+            return default.rstrip("/")
     # Try env var
     env_url = os.environ.get("DATASETTE_URL")
     if env_url:
@@ -62,7 +65,7 @@ def _resolve_instance(instance, config_file):
     raise click.ClickException(
         "No instance specified. Use -i <url-or-alias>, or configure a default:\n\n"
         "    dclient alias add <name> <url>\n"
-        "    dclient alias default <name>\n\n"
+        "    dclient default instance <name-or-url>\n\n"
         "Or set the DATASETTE_URL environment variable."
     )
 
@@ -75,8 +78,13 @@ def _resolve_database(database, instance_alias, config_file):
     if instance_alias:
         config = _load_config(config_file)
         instances = config.get("instances", {})
-        if instance_alias in instances:
-            default_db = instances[instance_alias].get("default_database")
+        key = instance_alias
+        if key not in instances and (
+            key.startswith("http://") or key.startswith("https://")
+        ):
+            key = _instance_alias_for_url(key, config_file)
+        if key in instances:
+            default_db = instances[key].get("default_database")
             if default_db:
                 return default_db
     # Try env var
@@ -85,7 +93,7 @@ def _resolve_database(database, instance_alias, config_file):
         return env_db
     raise click.ClickException(
         "No database specified. Use -d <name>, or configure a default:\n\n"
-        "    dclient alias default-db <alias> <database>\n\n"
+        "    dclient default database <alias-or-url> <database>\n\n"
         "Or set the DATASETTE_DATABASE environment variable."
     )
 
@@ -902,29 +910,56 @@ def alias_remove(name):
         raise click.ClickException("No such alias")
 
 
-@alias.command(name="default")
-@click.argument("name", required=False, default=None)
+def _resolve_instance_key(alias_or_url, config):
+    instances = config.get("instances", {})
+    if alias_or_url in instances:
+        return alias_or_url
+    if alias_or_url.startswith("http://") or alias_or_url.startswith("https://"):
+        normalized = alias_or_url.rstrip("/")
+        for name, inst in instances.items():
+            if inst.get("url", "").rstrip("/") == normalized:
+                return name
+        raise click.ClickException(f"No such instance URL: {alias_or_url}")
+    raise click.ClickException(f"No such alias: {alias_or_url}")
+
+
+# -- default command group --
+
+
+@cli.group()
+def default():
+    "Manage default instance and database"
+
+
+@default.command(name="instance")
+@click.argument("alias_or_url", required=False, default=None)
 @click.option("--clear", is_flag=True, help="Clear default instance")
-def alias_default(name, clear):
+def default_instance(alias_or_url, clear):
     """
     Set or show the default instance
 
     Example usage:
 
     \b
-        dclient alias default prod
-        dclient alias default
-        dclient alias default --clear
+        dclient default instance prod
+        dclient default instance https://myapp.datasette.cloud
+        dclient default instance
+        dclient default instance --clear
     """
     config_file = get_config_dir() / "config.json"
     config = _load_config(config_file)
     if clear:
         config["default_instance"] = None
         _save_config(config_file, config)
-    elif name:
-        if name not in config.get("instances", {}):
-            raise click.ClickException(f"No such alias: {name}")
-        config["default_instance"] = name
+    elif alias_or_url:
+        if alias_or_url.startswith("http://") or alias_or_url.startswith("https://"):
+            try:
+                key = _resolve_instance_key(alias_or_url, config)
+            except click.ClickException:
+                key = alias_or_url.rstrip("/")
+        else:
+            key = _resolve_instance_key(alias_or_url, config)
+        config["default_instance"] = key
         _save_config(config_file, config)
     else:
         default = config.get("default_instance")
@@ -934,37 +969,37 @@ def alias_default(name, clear):
             click.echo("No default instance set")
 
 
-@alias.command(name="default-db")
-@click.argument("alias_name")
+@default.command(name="database")
+@click.argument("alias_or_url")
 @click.argument("db", required=False, default=None)
-@click.option("--clear", is_flag=True, help="Clear default database for this alias")
-def alias_default_db(alias_name, db, clear):
+@click.option("--clear", is_flag=True, help="Clear default database for this instance")
+def default_database(alias_or_url, db, clear):
     """
-    Set or show the default database for an alias
+    Set or show the default database for an instance
 
     Example usage:
 
     \b
-        dclient alias default-db prod main
-        dclient alias default-db prod
-        dclient alias default-db prod --clear
+        dclient default database prod main
+        dclient default database https://myapp.datasette.cloud main
+        dclient default database prod
+        dclient default database prod --clear
     """
     config_file = get_config_dir() / "config.json"
     config = _load_config(config_file)
-    if alias_name not in config.get("instances", {}):
-        raise click.ClickException(f"No such alias: {alias_name}")
+    instance_key = _resolve_instance_key(alias_or_url, config)
     if clear:
-        config["instances"][alias_name]["default_database"] = None
+        config["instances"][instance_key]["default_database"] = None
         _save_config(config_file, config)
     elif db:
-        config["instances"][alias_name]["default_database"] = db
+        config["instances"][instance_key]["default_database"] = db
         _save_config(config_file, config)
     else:
-        default_db = config["instances"][alias_name].get("default_database")
+        default_db = config["instances"][instance_key].get("default_database")
         if default_db:
             click.echo(default_db)
         else:
-            click.echo(f"No default database set for {alias_name}")
+            click.echo(f"No default database set for {instance_key}")
 
 
 # -- auth command group --
diff --git a/docs/aliases.md b/docs/aliases.md
index 8399085..4c4255d 100644
--- a/docs/aliases.md
+++ b/docs/aliases.md
@@ -13,28 +13,7 @@ Once registered, you can pass an alias to commands using the `-i` flag:
 
     dclient query fixtures "select * from news limit 1" -i latest
 
-## Default instance
-
-Set a default instance so you don't need `-i` every time:
-
-    dclient alias default latest
-
-Now commands will use `latest` automatically:
-
-    dclient databases
-    dclient tables -d fixtures
-
-## Default database
-
-Set a default database for an alias:
-
-    dclient alias default-db latest fixtures
-
-Now you can run bare SQL queries directly:
-
-    dclient "select * from facetable limit 5"
-
-This uses the default instance and default database.
+See [Defaults](defaults.md) for default instance and default database settings.
 
 ## dclient alias --help
 <!-- [[[cog
@@ -57,11 +36,9 @@ Options:
   --help  Show this message and exit.
 
 Commands:
-  add         Add an alias for a Datasette instance
-  default     Set or show the default instance
-  default-db  Set or show the default database for an alias
-  list        List aliases
-  remove      Remove an alias
+  add     Add an alias for a Datasette instance
+  list    List aliases
+  remove  Remove an alias
 
 ```
 <!-- [[[end]]] -->
@@ -137,59 +114,3 @@ Options:
 
 ```
 <!-- [[[end]]] -->
-
-## dclient alias default --help
-
-<!-- [[[cog
-import cog
-result = runner.invoke(cli.cli, ["alias", "default", "--help"])
-help = result.output.replace("Usage: cli", "Usage: dclient")
-cog.out(
-    "```\n{}\n```".format(help)
-)
-]]] -->
-```
-Usage: dclient alias default [OPTIONS] [NAME]
-
-  Set or show the default instance
-
-  Example usage:
-
-      dclient alias default prod
-      dclient alias default
-      dclient alias default --clear
-
-Options:
-  --clear  Clear default instance
-  --help   Show this message and exit.
-
-```
-<!-- [[[end]]] -->
-
-## dclient alias default-db --help
-
-<!-- [[[cog
-import cog
-result = runner.invoke(cli.cli, ["alias", "default-db", "--help"])
-help = result.output.replace("Usage: cli", "Usage: dclient")
-cog.out(
-    "```\n{}\n```".format(help)
-)
-]]] -->
-```
-Usage: dclient alias default-db [OPTIONS] ALIAS_NAME [DB]
-
-  Set or show the default database for an alias
-
-  Example usage:
-
-      dclient alias default-db prod main
-      dclient alias default-db prod
-      dclient alias default-db prod --clear
-
-Options:
-  --clear  Clear default database for this alias
-  --help   Show this message and exit.
-
-```
-<!-- [[[end]]] -->
diff --git a/docs/defaults.md b/docs/defaults.md
new file mode 100644
index 0000000..b53c334
--- /dev/null
+++ b/docs/defaults.md
@@ -0,0 +1,106 @@
+# Defaults
+
+Set a default instance so you don't need `-i` every time:
+
+    dclient default instance latest
+
+Now commands will use `latest` automatically:
+
+    dclient databases
+    dclient tables -d fixtures
+
+Set a default database for an alias or instance URL:
+
+    dclient default database latest fixtures
+    dclient default database https://latest.datasette.io fixtures
+
+Now you can run bare SQL queries directly:
+
+    dclient "select * from facetable limit 5"
+
+This uses the default instance and default database.
+
+## dclient default --help
+<!-- [[[cog
+import cog
+from dclient import cli
+from click.testing import CliRunner
+runner = CliRunner()
+result = runner.invoke(cli.cli, ["default", "--help"])
+help = result.output.replace("Usage: cli", "Usage: dclient")
+cog.out(
+    "```\n{}\n```".format(help)
+)
+]]] -->
+```
+Usage: dclient default [OPTIONS] COMMAND [ARGS]...
+
+  Manage default instance and database
+
+Options:
+  --help  Show this message and exit.
+
+Commands:
+  database  Set or show the default database for an instance
+  instance  Set or show the default instance
+
+```
+<!-- [[[end]]] -->
+
+## dclient default instance --help
+
+<!-- [[[cog
+import cog
+result = runner.invoke(cli.cli, ["default", "instance", "--help"])
+help = result.output.replace("Usage: cli", "Usage: dclient")
+cog.out(
+    "```\n{}\n```".format(help)
+)
+]]] -->
+```
+Usage: dclient default instance [OPTIONS] [ALIAS_OR_URL]
+
+  Set or show the default instance
+
+  Example usage:
+
+      dclient default instance prod
+      dclient default instance https://myapp.datasette.cloud
+      dclient default instance
+      dclient default instance --clear
+
+Options:
+  --clear  Clear default instance
+  --help   Show this message and exit.
+
+```
+<!-- [[[end]]] -->
+
+## dclient default database --help
+
+<!-- [[[cog
+import cog
+result = runner.invoke(cli.cli, ["default", "database", "--help"])
+help = result.output.replace("Usage: cli", "Usage: dclient")
+cog.out(
+    "```\n{}\n```".format(help)
+)
+]]] -->
+```
+Usage: dclient default database [OPTIONS] ALIAS_OR_URL [DB]
+
+  Set or show the default database for an instance
+
+  Example usage:
+
+      dclient default database prod main
+      dclient default database https://myapp.datasette.cloud main
+      dclient default database prod
+      dclient default database prod --clear
+
+Options:
+  --clear  Clear default database for this instance
+  --help   Show this message and exit.
+
+```
+<!-- [[[end]]] -->
diff --git a/docs/index.md b/docs/index.md
index dda58da..0b43234 100644
--- a/docs/index.md
+++ b/docs/index.md
@@ -35,6 +35,7 @@ maxdepth: 3
 ---
 queries
 aliases
+defaults
 authentication
 inserting
 environment
diff --git a/tests/test_alias_v2.py b/tests/test_alias_v2.py
index e93902d..173382e 100644
--- a/tests/test_alias_v2.py
+++ b/tests/test_alias_v2.py
@@ -1,4 +1,4 @@
-"""Tests for v2 alias command: default, default-db subcommands."""
+"""Tests for v2 defaults command: instance and database subcommands."""
 
 from click.testing import CliRunner
 from dclient.cli import cli
@@ -15,16 +15,16 @@ def test_alias_default_workflow(mocker, tmpdir):
     assert result.exit_code == 0
 
     # No default yet
-    result = runner.invoke(cli, ["alias", "default"])
+    result = runner.invoke(cli, ["default", "instance"])
     assert result.exit_code == 0
     assert "No default instance set" in result.output
 
     # Set default
-    result = runner.invoke(cli, ["alias", "default", "prod"])
+    result = runner.invoke(cli, ["default", "instance", "prod"])
     assert result.exit_code == 0
 
     # Show default
-    result = runner.invoke(cli, ["alias", "default"])
+    result = runner.invoke(cli, ["default", "instance"])
     assert result.exit_code == 0
     assert result.output.strip() == "prod"
 
@@ -34,17 +34,17 @@ def test_alias_default_workflow(mocker, tmpdir):
     assert "* prod" in result.output
 
     # Clear default
-    result = runner.invoke(cli, ["alias", "default", "--clear"])
+    result = runner.invoke(cli, ["default", "instance", "--clear"])
     assert result.exit_code == 0
 
-    result = runner.invoke(cli, ["alias", "default"])
+    result = runner.invoke(cli, ["default", "instance"])
     assert "No default instance set" in result.output
 
 
 def test_alias_default_unknown_alias(mocker, tmpdir):
     mocker.patch("dclient.cli.get_config_dir", return_value=pathlib.Path(tmpdir))
     runner = CliRunner()
-    result = runner.invoke(cli, ["alias", "default", "nonexistent"])
+    result = runner.invoke(cli, ["default", "instance", "nonexistent"])
     assert result.exit_code == 1
     assert "No such alias" in result.output
 
@@ -58,16 +58,16 @@ def test_alias_default_db_workflow(mocker, tmpdir):
     assert result.exit_code == 0
 
     # No default database yet
-    result = runner.invoke(cli, ["alias", "default-db", "prod"])
+    result = runner.invoke(cli, ["default", "database", "prod"])
     assert result.exit_code == 0
     assert "No default database set" in result.output
 
     # Set default database
-    result = runner.invoke(cli, ["alias", "default-db", "prod", "main"])
+    result = runner.invoke(cli, ["default", "database", "prod", "main"])
     assert result.exit_code == 0
 
     # Show default database
-    result = runner.invoke(cli, ["alias", "default-db", "prod"])
+    result = runner.invoke(cli, ["default", "database", "prod"])
     assert result.exit_code == 0
     assert result.output.strip() == "main"
 
@@ -76,17 +76,17 @@ def test_alias_default_db_workflow(mocker, tmpdir):
     assert "(db: main)" in result.output
 
     # Clear default database
-    result = runner.invoke(cli, ["alias", "default-db", "prod", "--clear"])
+    result = runner.invoke(cli, ["default", "database", "prod", "--clear"])
     assert result.exit_code == 0
 
-    result = runner.invoke(cli, ["alias", "default-db", "prod"])
+    result = runner.invoke(cli, ["default", "database", "prod"])
     assert "No default database set" in result.output
 
 
 def test_alias_default_db_unknown_alias(mocker, tmpdir):
     mocker.patch("dclient.cli.get_config_dir", return_value=pathlib.Path(tmpdir))
     runner = CliRunner()
-    result = runner.invoke(cli, ["alias", "default-db", "nonexistent", "main"])
+    result = runner.invoke(cli, ["default", "database", "nonexistent", "main"])
     assert result.exit_code == 1
     assert "No such alias" in result.output
 
@@ -97,7 +97,7 @@ def test_alias_remove_clears_default(mocker, tmpdir):
     runner = CliRunner()
 
     runner.invoke(cli, ["alias", "add", "prod", "https://prod.example.com"])
-    runner.invoke(cli, ["alias", "default", "prod"])
+    runner.invoke(cli, ["default", "instance", "prod"])
 
     # Verify it's set
     config = json.loads((pathlib.Path(tmpdir) / "config.json").read_text())
@@ -109,3 +109,31 @@ def test_alias_remove_clears_default(mocker, tmpdir):
     config = json.loads((pathlib.Path(tmpdir) / "config.json").read_text())
     assert config["default_instance"] is None
     assert "prod" not in config["instances"]
+
+
+def test_default_instance_accepts_url(mocker, tmpdir):
+    mocker.patch("dclient.cli.get_config_dir", return_value=pathlib.Path(tmpdir))
+    runner = CliRunner()
+
+    runner.invoke(cli, ["alias", "add", "prod", "https://prod.example.com"])
+    result = runner.invoke(cli, ["default", "instance", "https://prod.example.com"])
+    assert result.exit_code == 0
+
+    result = runner.invoke(cli, ["default", "instance"])
+    assert result.exit_code == 0
+    assert result.output.strip() == "prod"
+
+
+def test_default_database_accepts_url(mocker, tmpdir):
+    mocker.patch("dclient.cli.get_config_dir", return_value=pathlib.Path(tmpdir))
+    runner = CliRunner()
+
+    runner.invoke(cli, ["alias", "add", "prod", "https://prod.example.com"])
+    result = runner.invoke(
+        cli, ["default", "database", "https://prod.example.com", "main"]
+    )
+    assert result.exit_code == 0
+
+    result = runner.invoke(cli, ["default", "database", "prod"])
+    assert result.exit_code == 0
+    assert result.output.strip() == "main"