Standardize OpenAPI spec references to .yaml across docs

 (#5586)

Co-authored-by: fern-api[bot] <115122769+fern-api[bot]@users.noreply.github.com>

Author: fern-api[bot]

fern/products/api-def/openapi/extensions/api-version.mdx

@@ -7,7 +7,7 @@ description: Configure API version schemes and headers using `x-fern-version` ex
 
 You can define your API version scheme, such as a `X-API-Version` header. The supported versions and default value are specified like so:
 
-```yaml title="openapi.yaml"
+```yaml title="openapi.yml"
 x-fern-version:
   header: X-API-Version
   default: "2.0.0"

fern/products/api-def/openapi/extensions/method-names.mdx

@@ -14,7 +14,7 @@ Use the `x-fern-sdk-group-name` and `x-fern-sdk-method-name` extensions to contr
 In the example below, Fern will generate a
 method called `client.users.create()` for the `POST /users` endpoint.
 
-```yaml title="openapi.yaml" {4-5}
+```yaml title="openapi.yml" {4-5}
 paths:
   /users:
     post:
@@ -28,7 +28,7 @@ If you omit the `x-fern-sdk-group-name` extension, the generated SDK method
 will live at the root of the client rather than nested under a resource group.
 In the example below, Fern will generate a method called `client.send()`:
 
-```yaml title="openapi.yaml" {4}
+```yaml title="openapi.yml" {4}
 paths:
   /send:
     post:
@@ -46,7 +46,7 @@ The generated SDK method preserves the order of group names.
 
 In the example below, Fern will generate a method called `client.users.notifications.send()`:
 
-```yaml title="openapi.yaml"
+```yaml title="openapi.yml"
 paths:
   /users/notifications:
     post:

fern/products/cli-generator/openapi-extensions.mdx

@@ -16,7 +16,7 @@ The CLI generator reads several [Fern OpenAPI extensions](/learn/api-definitions
 
 Determines the subcommand group hierarchy. Each list element becomes a nested subcommand, with names converted from camelCase to kebab-case.
 
-```yaml title="openapi.yaml" {4-6}
+```yaml title="openapi.yml" {4-6}
 paths:
   /scheduled-events/{uuid}/invitees:
     get:
@@ -32,7 +32,7 @@ Produces: `cli scheduled-events invitees list-event-invitees`
 
 Sets the leaf command name (used as-is).
 
-```yaml title="openapi.yaml" {4}
+```yaml title="openapi.yml" {4}
 paths:
   /users/me:
     get:
@@ -53,7 +53,7 @@ See [SDK method names](/learn/api-definitions/openapi/extensions/method-names) f
 
 Excludes operations or parameters from the generated CLI. An ignored operation produces no command; an ignored parameter produces no flag.
 
-```yaml title="openapi.yaml" {4}
+```yaml title="openapi.yml" {4}
 paths:
   /internal/debug:
     get:
@@ -62,7 +62,7 @@ paths:
 
 At the parameter level:
 
-```yaml title="openapi.yaml" {7}
+```yaml title="openapi.yml" {7}
 paths:
   /users:
     get:
@@ -91,7 +91,7 @@ Adds a status badge next to the command in `--help` output.
 | `deprecated` | `[Deprecated]` |
 | `legacy` | `[Legacy]` |
 
-```yaml title="openapi.yaml" {4}
+```yaml title="openapi.yml" {4}
 paths:
   /v2/reports:
     get:
@@ -108,7 +108,7 @@ See [Availability](/learn/api-definitions/openapi/extensions/availability) for m
 
 Overrides the CLI flag name derived from a parameter. By default, parameter names are converted to kebab-case for use as flags.
 
-```yaml title="openapi.yaml" {9}
+```yaml title="openapi.yml" {9}
 paths:
   /users:
     get:
@@ -130,7 +130,7 @@ See [Customize parameter names](/learn/api-definitions/openapi/extensions/parame
 
 Enables auto-pagination for an endpoint. When present, the CLI recognizes `--page-all`, `--page-limit`, and `--page-delay` flags for that command.
 
-```yaml title="openapi.yaml" {5-8}
+```yaml title="openapi.yml" {5-8}
 paths:
   /plants:
     get:

fern/products/docs/pages/getting-started/project-structure.mdx

@@ -19,7 +19,7 @@ The configuration files for your docs live in the `fern` folder:
     </Folder>
     <Folder name="snippets" comment="Reusable MDX snippets" />
     <File name="docs.yml" comment="Defines navigation, theme, and hosting" />
-    <File name="openapi.yaml" comment="API definition (OpenAPI, AsyncAPI, etc.)" />
+    <File name="openapi.yml" comment="API definition (OpenAPI, AsyncAPI, etc.)" />
     <File name="generators.yml" comment="References specs, configures SDKs" />
     <File name="fern.config.json" comment="Organization name and CLI version" />
     <File name="styles.css" comment="Custom CSS styles" />
@@ -61,6 +61,10 @@ The `assets` folder contains any images or videos used in your documentation. Yo
 
 The `docs.yml` file is the heart of your Fern documentation site. This configuration file controls your documentation's navigation structure, visual design, site functionality, and hosting settings. Only files referenced in your `docs.yml` navigation (or discovered via a [`folder` configuration](/learn/docs/configuration/navigation#auto-populate-from-folder)) are included in builds — any unreferenced files are ignored.
 
+<Note>
+Fern treats `.yml` and `.yaml` extensions identically. This applies to all YAML files in a Fern project, including `docs.yml`, `generators.yml`, and API specification files.
+</Note>
+
 For complete configuration options, see the [`docs.yml` reference](/docs/configuration/site-level-settings).
 
 <CodeBlock title="Example fern/docs.yml">
@@ -132,7 +136,7 @@ To generate [API Reference](/docs/api-references/generate-api-ref) documentation
     ```yaml title="generators.yml"
     api:
       specs:
-        - openapi: openapi.yaml
+        - openapi: openapi.yml
     ```
 
     You can optionally [add an overlays file](/learn/api-definitions/openapi/overlays) for additional customizations. To see this in practice, check out [Fluidstack's Fern configuration](https://github.com/fluidstackio/fern-config/tree/main/fern/openapi).
@@ -144,7 +148,7 @@ To generate [API Reference](/docs/api-references/generate-api-ref) documentation
     ```yaml title="generators.yml"
     api:
       specs:
-        - openapi: openapi.yaml
+        - openapi: openapi.yml
         - asyncapi: asyncapi.yaml
     ```
 
@@ -162,7 +166,7 @@ To generate [API Reference](/docs/api-references/generate-api-ref) documentation
           <File name="overrides.yaml" comment="Optional" />
         </Folder>
         <Folder name="user-api" defaultOpen>
-          <File name="openapi.yaml" highlighted />
+          <File name="openapi.yml" highlighted />
           <File name="generators.yml" />
           <File name="overrides.yaml" comment="Optional" />
         </Folder>

fern/products/docs/pages/getting-started/quickstart.mdx

@@ -88,7 +88,7 @@ This guide covers the CLI path. A browser-based guided setup also exists at http
         <File name="docs.yml" comment="Defines navigation, theme, and hosting details"/>
         <File name="fern.config.json" comment="Specifies org name and CLI version"/>
         <File name="generators.yml" comment="Configures SDK generation"/>
-        <File name="openapi.yaml" comment="API definition"/>
+        <File name="openapi.yml" comment="API definition"/>
       </Folder>
       <File name="README.md" />
     </Files>
@@ -182,7 +182,7 @@ This guide covers the CLI path. A browser-based guided setup also exists at http
     </Accordion>
     <Accordion title='Add an API Reference' >
 
-    If you cloned the starter template, you already have an `openapi.yaml` file with sample API definitions. If you started from scratch, add your OpenAPI spec:
+    If you cloned the starter template, you already have an `openapi.yml` file with sample API definitions (both `.yml` and `.yaml` work interchangeably). If you started from scratch, add your OpenAPI spec:
 
     ```bash
     fern init --openapi /path/to/openapi.yml

fern/products/sdks/deep-dives/customize-method-names.mdx

@@ -41,7 +41,7 @@ Fern generates SDK methods using your configured group and method names. Casing
 
 Configure how endpoints map to SDK method and group names in your API definition:
 
-```yaml title="openapi.yaml" {4-5}
+```yaml title="openapi.yml" {4-5}
 paths:
   /users:
     post:

fern/snippets/open-api-method-names.mdx

@@ -7,7 +7,7 @@ Use the `x-fern-sdk-group-name` and `x-fern-sdk-method-name` extensions to contr
 In the example below, Fern will generate a
 method called `client.users.create()` for the `POST /users` endpoint.
 
-```yaml title="openapi.yaml" {4-5}
+```yaml title="openapi.yml" {4-5}
 paths:
   /users:
     post:
@@ -21,7 +21,7 @@ If you omit the `x-fern-sdk-group-name` extension, the generated SDK method
 will live at the root of the client rather than nested under a resource group.
 In the example below, Fern will generate a method called `client.send()`:
 
-```yaml title="openapi.yaml" {4}
+```yaml title="openapi.yml" {4}
 paths:
   /send:
     post:
@@ -39,7 +39,7 @@ The generated SDK method preserves the order of group names.
 
 In the example below, Fern will generate a method called `client.users.notifications.send()`:
 
-```yaml title="openapi.yaml"
+```yaml title="openapi.yml"
 paths:
   /users/notifications:
     post: