chore(cli): add validate command (#7438)

add validate command

---------

Co-authored-by: Will Fu-Hinthorn <will@langchain.dev>

libs/cli/langgraph_cli/cli.py

@@ -817,6 +817,48 @@ def dev(
     )
 
 
+# ---------------------------------------------------------------------------
+# validate command
+# ---------------------------------------------------------------------------
+
+
+@OPT_CONFIG
+@cli.command(help="✅ Validate the LangGraph configuration file.")
+@log_command
+def validate(config: pathlib.Path):
+    import json
+
+    try:
+        with open(config) as f:
+            raw_config = json.load(f)
+    except json.JSONDecodeError as e:
+        raise click.UsageError(f"Invalid JSON in {config}: {e.args[0]}") from None
+
+    # Check for unknown keys before validation so they show alongside any error.
+    unknown_warnings = langgraph_cli.config.get_unknown_keys(raw_config)
+
+    try:
+        config_json = langgraph_cli.config.validate_config_file(config)
+    except (click.UsageError, ValueError) as e:
+        click.secho(f"Error: {e}", fg="red", err=True)
+        if unknown_warnings:
+            click.echo(err=True)
+            for warning in unknown_warnings:
+                click.secho(f"  warning: {warning}", fg="yellow", err=True)
+        raise SystemExit(1) from None
+
+    num_graphs = len(config_json.get("graphs", {}))
+    click.secho(
+        f"Configuration file {config} is valid. "
+        f"({num_graphs} graph{'s' if num_graphs != 1 else ''} found)",
+        fg="green",
+    )
+    if unknown_warnings:
+        click.echo()
+        for warning in unknown_warnings:
+            click.secho(f"  warning: {warning}", fg="yellow")
+
+
 # ---------------------------------------------------------------------------
 # new command
 # ---------------------------------------------------------------------------