diff --git a/src/command/dev-call/cmd.ts b/src/command/dev-call/cmd.ts
index 10534a1268..a6e2f63316 100644
--- a/src/command/dev-call/cmd.ts
+++ b/src/command/dev-call/cmd.ts
@@ -2,7 +2,7 @@ import { Command } from "cliffy/command/mod.ts";
 import { quartoConfig } from "../../core/quarto.ts";
 import { commands } from "../command.ts";
 import { buildJsCommand } from "./build-artifacts/cmd.ts";
-import { hidden } from "../../core/lib/external/colors.ts";
+import { validateYamlCommand } from "./validate-yaml/cmd.ts";
 
 type CommandOptionInfo = {
   name: string;
@@ -70,4 +70,5 @@ export const devCallCommand = new Command()
     Deno.exit(1);
   })
   .command("cli-info", generateCliInfoCommand)
+  .command("validate-yaml", validateYamlCommand)
   .command("build-artifacts", buildJsCommand);
diff --git a/src/command/dev-call/validate-yaml/cmd.ts b/src/command/dev-call/validate-yaml/cmd.ts
new file mode 100644
index 0000000000..dc10c398a6
--- /dev/null
+++ b/src/command/dev-call/validate-yaml/cmd.ts
@@ -0,0 +1,88 @@
+/*
+ * cmd.ts
+ *
+ * Copyright (C) 2025 Posit Software, PBC
+ */
+
+import { Command } from "cliffy/command/mod.ts";
+import { initYamlIntelligenceResourcesFromFilesystem } from "../../../core/schema/utils.ts";
+import { readAndValidateYamlFromMappedString } from "../../../core/lib/yaml-schema/validated-yaml.ts";
+import { mappedStringFromFile } from "../../../core/mapped-text.ts";
+import {
+  getSchemaDefinition,
+  setSchemaDefinition,
+} from "../../../core/lib/yaml-validation/schema.ts";
+import { error } from "../../../deno_ral/log.ts";
+import { tidyverseFormatError } from "../../../core/lib/errors.ts";
+import {
+  convertFromYaml,
+  getSchemaSchemas,
+} from "../../../core/lib/yaml-schema/from-yaml.ts";
+
+const getSchema = async (schemaNameOrFile: string) => {
+  if (schemaNameOrFile.endsWith(".yml")) {
+    getSchemaSchemas();
+    // it's a file, we load it, validate it against the schema schema
+    // and then return it
+    const file = mappedStringFromFile(schemaNameOrFile);
+    const schema = getSchemaDefinition("schema/schema");
+    const result = await readAndValidateYamlFromMappedString(
+      file,
+      schema,
+    );
+    if (result.yamlValidationErrors.length) {
+      error("Schema file is not valid");
+      for (const err of result.yamlValidationErrors) {
+        error(tidyverseFormatError(err.niceError), { colorize: false });
+      }
+      Deno.exit(1);
+    }
+    const schemaName = `user-schema-${schemaNameOrFile}`;
+    const newSchema = convertFromYaml(result.yaml);
+    newSchema.$id = schemaName;
+    setSchemaDefinition(newSchema);
+    return getSchemaDefinition(schemaName);
+  } else {
+    // it's a schema name, we get it from the schema registry
+    // and return it
+    return getSchemaDefinition(schemaNameOrFile);
+  }
+};
+
+export const validateYamlCommand = new Command()
+  .name("validate-yaml")
+  .hidden()
+  .arguments("<input:string>")
+  .option(
+    "-s, --schema [schema:string]",
+    "Name of schema in Quarto's definitions.yml. If string ends with .yml, it is treated as a file name for a new schema, which is validated, loaded, and then used.",
+  )
+  .option(
+    "--json",
+    "If set, output error messages in JSON format.",
+  )
+  .description(
+    "Validates a YAML file against Quarto's schemas.\n\n",
+  )
+  .action(async (options: any, input: string) => {
+    await initYamlIntelligenceResourcesFromFilesystem();
+    if (!options.schema) {
+      throw new Error("Schema name or file is required");
+    }
+    const file = mappedStringFromFile(input);
+    const schema = await getSchema(options.schema);
+    const result = await readAndValidateYamlFromMappedString(
+      file,
+      schema,
+    );
+    if (options.json) {
+      console.log(JSON.stringify(result.yamlValidationErrors, null, 2));
+    } else {
+      for (const err of result.yamlValidationErrors) {
+        error(tidyverseFormatError(err.niceError), { colorize: false });
+      }
+    }
+    if (result.yamlValidationErrors.length) {
+      Deno.exit(1);
+    }
+  });