diff --git a/CHANGELOG.md b/CHANGELOG.md
index ba67ba560..679bb4392 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -23,6 +23,8 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 * `ui.value_box()`, `ui.layout_columns()` and `ui.layout_column_wrap()` now all have `min_height` and `max_height` arguments. These are useful in filling layouts, like `ui.page_fillable()`, `ui.page_sidebar(fillable=True)` or `ui.page_navbar(fillable=True)`. For example, you can use `ui.layout_columns(min_height=300, max_height=500)` to ensure that a set of items (likely arranged in a row of columns) are always between 300 and 500 pixels tall. (#1223)
 
+* Added an error console which displays errors in the browser's UI. This is enabled by default when running applications locally, and can be disabled with `shiny run --no-dev-mode`. It is not enabled for applications that are deployed to a server. (#1060)
+
 ### Bug fixes
 
 * On Windows, Shiny Express app files are now read in as UTF-8. (#1203)
diff --git a/shiny/_app.py b/shiny/_app.py
index f3c6c81d7..fb8dd2f50 100644
--- a/shiny/_app.py
+++ b/shiny/_app.py
@@ -438,7 +438,7 @@ def _render_page(self, ui: Tag | TagList, lib_prefix: str) -> RenderedHTML:
         ui_res = copy.copy(ui)
         # Make sure requirejs, jQuery, and Shiny come before any other dependencies.
         # (see require_deps() for a comment about why we even include it)
-        ui_res.insert(0, [require_deps(), jquery_deps(), shiny_deps()])
+        ui_res.insert(0, [require_deps(), jquery_deps(), *shiny_deps()])
         rendered = HTMLDocument(ui_res).render(lib_prefix=lib_prefix)
         self._ensure_web_dependencies(rendered["dependencies"])
         return rendered
@@ -449,7 +449,7 @@ def _render_page_from_file(self, file: Path, lib_prefix: str) -> RenderedHTML:
 
         doc = HTMLTextDocument(
             page_html,
-            deps=[require_deps(), jquery_deps(), shiny_deps()],
+            deps=[require_deps(), jquery_deps(), *shiny_deps()],
             deps_replace_pattern='<meta name="shiny-dependency-placeholder" content="">',
         )
 
diff --git a/shiny/_main.py b/shiny/_main.py
index 0e384e879..b040f379c 100644
--- a/shiny/_main.py
+++ b/shiny/_main.py
@@ -143,6 +143,13 @@ def main() -> None:
     help="Launch app browser after app starts, using the Python webbrowser module.",
     show_default=True,
 )
+@click.option(
+    "--dev-mode/--no-dev-mode",
+    is_flag=True,
+    default=True,
+    help="Dev mode",
+    show_default=True,
+)
 @no_example()
 def run(
     app: str | shiny.App,
@@ -159,6 +166,7 @@ def run(
     app_dir: str,
     factory: bool,
     launch_browser: bool,
+    dev_mode: bool,
     **kwargs: object,
 ) -> None:
     reload_includes_list = reload_includes.split(",")
@@ -177,6 +185,7 @@ def run(
         app_dir=app_dir,
         factory=factory,
         launch_browser=launch_browser,
+        dev_mode=dev_mode,
         **kwargs,
     )
 
@@ -196,6 +205,7 @@ def run_app(
     app_dir: Optional[str] = ".",
     factory: bool = False,
     launch_browser: bool = False,
+    dev_mode: bool = True,
     **kwargs: object,
 ) -> None:
     """
@@ -276,6 +286,8 @@ def run_app(
 
     os.environ["SHINY_HOST"] = host
     os.environ["SHINY_PORT"] = str(port)
+    if dev_mode:
+        os.environ["SHINY_DEV_MODE"] = "1"
 
     if isinstance(app, str):
         # Remove ":app" suffix if present. Normally users would just pass in the
diff --git a/shiny/html_dependencies.py b/shiny/html_dependencies.py
index a6dc1f628..4c0867932 100644
--- a/shiny/html_dependencies.py
+++ b/shiny/html_dependencies.py
@@ -1,14 +1,30 @@
+from __future__ import annotations
+
+import os
+
 from htmltools import HTMLDependency
 
 
-def shiny_deps() -> HTMLDependency:
-    return HTMLDependency(
-        name="shiny",
-        version="0.0.1",
-        source={"package": "shiny", "subdir": "www/shared/"},
-        script={"src": "shiny.js"},
-        stylesheet={"href": "shiny.min.css"},
-    )
+def shiny_deps() -> list[HTMLDependency]:
+    deps = [
+        HTMLDependency(
+            name="shiny",
+            version="0.0.1",
+            source={"package": "shiny", "subdir": "www/shared/"},
+            script={"src": "shiny.js"},
+            stylesheet={"href": "shiny.min.css"},
+        )
+    ]
+    if os.getenv("SHINY_DEV_MODE") == "1":
+        deps.append(
+            HTMLDependency(
+                "shiny-devmode",
+                version="0.0.1",
+                head="<script>window.__SHINY_DEV_MODE__ = true;</script>",
+            )
+        )
+
+    return deps
 
 
 def jquery_deps() -> HTMLDependency: