assertContentType("application/msword", "test/text1.txt", "hoge.doc");
        assertContentType("application/msword", "extractor/msoffice/test.doc", "hoge.doc");
        assertContentType("application/vnd.ms-excel", "test/text1.txt", "hoge.xls");
        assertContentType("application/vnd.ms-excel", "extractor/msoffice/test.xls", "hoge.xls");
        assertContentType("application/vnd.ms-powerpoint", "test/text1.txt", "hoge.ppt");

### Top-level application { #top-level-application }

First, create the main, top-level, **FastAPI** application, and its *path operations*:

{* ../../docs_src/sub_applications/tutorial001.py hl[3, 6:8] *}

### Sub-application { #sub-application }

Then, create your sub-application, and its *path operations*.

# Bigger Applications - Multiple Files { #bigger-applications-multiple-files }

If you are building an application or a web API, it's rarely the case that you can put everything in a single file.

**FastAPI** provides a convenience tool to structure your application while keeping all the flexibility.

/// info

If you come from Flask, this would be the equivalent of Flask's Blueprints.

///

## An example file structure { #an-example-file-structure }

### Bigger Errors - Crashes { #bigger-errors-crashes }

Nevertheless, there might be cases where we write some code that **crashes the entire application** making Uvicorn and Python crash. 💥

For some types of applications you might want to add dependencies to the whole application.

Similar to the way you can [add `dependencies` to the *path operation decorators*](dependencies-in-path-operation-decorators.md){.internal-link target=_blank}, you can add them to the `FastAPI` application.

In that case, they will be applied to all the *path operations* in the application:

		{
			name:     "1",
			metadata: map[string]string{"content-type": "application/octet-stream", "etag": "de75a98baf2c6aef435b57dd0fc33c86", "x-amz-storage-class": "STANDARD"},
			want:     map[string]string{"content-type": "application/octet-stream", "etag": "de75a98baf2c6aef435b57dd0fc33c86"},
		},
		{
			name:     "2",

[19511] [INFO] Started server process [19511]
[19511] [INFO] Waiting for application startup.
[19511] [INFO] Application startup complete.
[19513] [INFO] Started server process [19513]
[19513] [INFO] Waiting for application startup.
[19513] [INFO] Application startup complete.
[19514] [INFO] Started server process [19514]
[19514] [INFO] Waiting for application startup.
[19514] [INFO] Application startup complete.
[19515] [INFO] Started server process [19515]

     <span style="background-color:#007166"><font color="#D3D7CF"> INFO </font></span>  Waiting for application startup.
     <span style="background-color:#007166"><font color="#D3D7CF"> INFO </font></span>  Application startup complete.

ff"},{"key":"frequency","value":"24h"}]},"compression":{"_":[{"key":"enable","value":"off"},{"key":"allow_encryption","value":"off"},{"key":"extensions","value":".txt,.log,.csv,.json,.tar,.xml,.bin"},{"key":"mime_types","value":"text/*,application/json,application/xml,binary/octet-stream"}]},"crawler":{"_":null},"credentials":{"_":null},"drive":{"_":[{"key":"max_timeout","value":""}]},"etcd":{"_":[{"key":"endpoints","value":""},{"key":"path_prefix","value":""},{"key":"coredns_path","value":"/sky...

### What is "Mounting" { #what-is-mounting }

"Mounting" means adding a complete "independent" application in a specific path, that then takes care of handling all the sub-paths.

This is different from using an `APIRouter` as a mounted application is completely independent. The OpenAPI and docs from your main application won't include anything from the mounted application, etc.