Because **FastAPI** is based on the **OpenAPI** specification, its APIs can be described in a standard format that many tools understand.

This makes it easy to generate up-to-date **documentation**, client libraries (<abbr title="Software Development Kits">**SDKs**</abbr>) in multiple languages, and **testing** or **automation workflows** that stay in sync with your code.

In this guide, you'll learn how to generate a **TypeScript SDK** for your FastAPI backend.

$ cd awesome-project
```

</div>

## Create a Virtual Environment { #create-a-virtual-environment }

When you start working on a Python project **for the first time**, create a virtual environment **<dfn title="there are other options, this is a simple guideline">inside your project</dfn>**.

/// tip

You only need to do this **once per project**, not every time you work.

///

//// tab | `venv`

## An app with callbacks { #an-app-with-callbacks }

Let's see all this with an example.

Imagine you develop an app that allows creating invoices.

These invoices will have an `id`, `title` (optional), `customer`, and `total`.

The user of your API (an external developer) will create an invoice in your API with a POST request.

Then your API will (let's imagine):

在這種情況下，你可能想要文件化說明該外部 API 應該長什麼樣子。它應該有哪些「路徑操作」、應該接受什麼 body、應該回傳什麼 response，等等。

## 帶有回呼的應用 { #an-app-with-callbacks }

我們用一個例子來看。

想像你開發了一個允許建立發票的應用。

這些發票會有 `id`、`title`（可選）、`customer` 和 `total`。

你的 API 的使用者（外部開發者）會透過一個 POST 請求在你的 API 中建立一張發票。

然後你的 API 會（讓我們想像）：

* 將發票寄給該外部開發者的某位客戶。
* 代收款項。
* 再把通知回傳給 API 使用者（外部開發者）。
    * 這會透過從「你的 API」向該外部開發者提供的「外部 API」送出 POST 請求完成（這就是「回呼」）。

        assertNotNull(tokensContent);
        assertEquals(2, tokensContent.size());

        List<AnalyzeToken> tokensTitle = analyzer.analyze(text, "title", lang);
        assertNotNull(tokensTitle);
        assertEquals(2, tokensTitle.size());

        // Test with null field
        List<AnalyzeToken> tokensNull = analyzer.analyze(text, null, lang);

        // Test executing BoostQuery with a complex BooleanQuery containing multiple clauses
        BooleanQuery.Builder boolBuilder = new BooleanQuery.Builder();
        boolBuilder.add(new TermQuery(new Term("title", "fess")), BooleanClause.Occur.MUST);
        boolBuilder.add(new PrefixQuery(new Term("content", "search")), BooleanClause.Occur.SHOULD);

      Contributor provides its Contributions) on an "AS IS" BASIS,
      WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or
      implied, including, without limitation, any warranties or conditions
      of TITLE, NON-INFRINGEMENT, MERCHANTABILITY, or FITNESS FOR A
      PARTICULAR PURPOSE. You are solely responsible for determining the
      appropriateness of using or redistributing the Work and assume any

      Contributor provides its Contributions) on an "AS IS" BASIS,
      WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or
      implied, including, without limitation, any warranties or conditions
      of TITLE, NON-INFRINGEMENT, MERCHANTABILITY, or FITNESS FOR A
      PARTICULAR PURPOSE. You are solely responsible for determining the
      appropriateness of using or redistributing the Work and assume any

      Contributor provides its Contributions) on an "AS IS" BASIS,
      WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or
      implied, including, without limitation, any warranties or conditions
      of TITLE, NON-INFRINGEMENT, MERCHANTABILITY, or FITNESS FOR A
      PARTICULAR PURPOSE. You are solely responsible for determining the
      appropriateness of using or redistributing the Work and assume any

        public boolean isLoggingSearchDocsEnabled() {
            return false;
        }

        @Override
        public String[] getLoggingSearchDocsFieldsAsArray() {
            return new String[] { "title", "url" };
        }

        @Override
        public String getPurgeByBots() {
            return "bot,crawler,spider";
        }

        @Override