By default, what the method `.openapi()` does is check the property `.openapi_schema` to see if it has contents and return them.

If it doesn't, it generates them using the utility function at `fastapi.openapi.utils.get_openapi`.

And that function `get_openapi()` receives as parameters:

* `title`: The OpenAPI title, shown in the docs.

![ReDoc](https://fastapi.tiangolo.com/img/index/index-02-redoc-simple.png)

### OpenAPI

**FastAPI** generates a "schema" with all your API using the **OpenAPI** standard for defining APIs.

#### "Schema"

A "schema" is a definition or description of something. Not the code that implements it, but just an abstract description.

          root = Optional.of(new BinaryNode(rng.nextInt(), Optional.<BinaryNode>absent(), root));
        }
        return root;
      }
    },
    RANDOM {
      /**
       * Generates a tree with topology selected uniformly at random from the topologies of binary
       * trees of the specified size.
       */
      @Override
      Optional<BinaryNode> createTree(int size, Random rng) {

import java.lang.reflect.Method;
import java.util.Map.Entry;
import junit.framework.TestSuite;

/**
 * A generator of {@code TestSuite} instances for testing {@code ByteSink} implementations.
 * Generates tests of all methods on a {@code ByteSink} given various inputs written to it as well
 * as sub-suites for testing the {@code CharSink} view in the same way.
 *
 * @author Colin Decker
 */

import java.lang.reflect.Method;
import java.util.Map.Entry;
import junit.framework.TestSuite;

/**
 * A generator of {@code TestSuite} instances for testing {@code ByteSink} implementations.
 * Generates tests of all methods on a {@code ByteSink} given various inputs written to it as well
 * as sub-suites for testing the {@code CharSink} view in the same way.
 *
 * @author Colin Decker
 */

import java.util.List;
import java.util.Map.Entry;
import java.util.stream.Stream;
import junit.framework.TestSuite;

/**
 * A generator of {@code TestSuite} instances for testing {@code CharSource} implementations.
 * Generates tests of all methods on a {@code CharSource} given various inputs the source is
 * expected to contain.
 *
 * @author Colin Decker
 */

import java.lang.reflect.Method;
import java.util.Map.Entry;
import java.util.Random;
import junit.framework.TestSuite;

/**
 * A generator of {@code TestSuite} instances for testing {@code ByteSource} implementations.
 * Generates tests of all methods on a {@code ByteSource} given various inputs the source is
 * expected to contain as well as sub-suites for testing the {@code CharSource} view and {@code
 * slice()} views in the same way.
 *

     * forms are equivalent (though not necessarily minimal, though we hope this
     * to be the case). Thus, this test is more of a regression test.
     *
     * Rough instructions to regenerate the test outputs and verify correctness:
     * - Temporarily change this test:
     * --- Comment out assertEquals.
     * --- System.out.println(input + " " + simplifyPath(input));

     * forms are equivalent (though not necessarily minimal, though we hope this
     * to be the case). Thus, this test is more of a regression test.
     *
     * Rough instructions to regenerate the test outputs and verify correctness:
     * - Temporarily change this test:
     * --- Comment out assertEquals.
     * --- System.out.println(input + " " + simplifyPath(input));

## Caveat

*Applications that use direct S3 API will work fine, however interactive users uploading content using (when POSTing to the presigned URL an app generates) a popup becomes visible on browser to provide client certs, you would have to manually cancel and continue. This may be annoying to use but there is no workaround for now.*

## Explore Further