For the efficiency of REST API development, I think that I will use tools for specification generation, code generation, style check, and automatic formatting.
For Python, here are some tools that I find useful.
The development editor is VS Code.

REST API related

Write the OpenAPI specification in yaml format, and generate the REST API interface specification and code.
Interface specifications
Server-side stub (controller, HTTP request / response model)
Client SDK for front-side REST API
Generating server stubs is very convenient.
If you generate Flask code in Python, you can even control a Flask app (wrapped in a library called connexion) that controls HTTP requests based on the OpenAPI Specification.
Since it validates HTTP requests based on the OpenAPI specification, you do not need to develop the validation code yourself.
For the client side, it can also be used as a stub server until the server side is completed.
The client SDK is also useful. It's easier than creating your own endpoints and requests.
The tools used are as follows.

Use	Tool name	Explanation	Link
Editing OpenAPI Specification	VSCode + OpenAPI Editor(Extensions)	Write OpenAPI Specification on VSCode. It is convenient to have a table of contents for paths and schemas on the left side.	https://marketplace.visualstudio.com/items?itemName=42Crunch.vscode-openapi
Reference to OpenAPI Specification	VSCode + Swagger Viewer(Extensions)	You can refer to the OpenAPI Specification as a document.	https://marketplace.visualstudio.com/items?itemName=Arjun.swagger-viewer
Validation of OpenAPI Specification	openapi-generator	CLIでValidation of OpenAPI Specificationができます。 You can also detect errors that the OpenAPI Editor cannot detect. However, there are some bugs that cannot be detected even with this. For example, the item set to required in the schema is not actually defined as a property. I notice these things because I get an error when I code-generate the server stub and start it.	https://github.com/OpenAPITools/openapi-generator
Code generation	openapi-generator	OpenAPI仕様（yamlファイル）からCode generation（サーバースタブ、クライアントSDK）できます。	Same as above
Document generation	openapi-genrator	Generate REST API interface specifications in HTML format.	Same as above

Python related

Generate a class diagram and class specifications from the developed code.
As a prerequisite for generating the class specification, you need to write a docstring.
Linter (style check) and Formatter (automatic format) are also useful for code development.
The tools used are as follows.

Use	Tool name	Explanation	Link
Generation class diagram	Pyreverse	Class diagram generation	https://pypi.org/project/pylint/
Generation of class specifications	Sphinx	Class specification generation	https://www.sphinx-doc.org/ja/master/ Sphinx installation instructions
docstring description assistance	VSCode + Python Docstring Generator	You can generate a docstring template from your code. For example, in the case of a method, the summary line, argument name, type, and return type are generated from the code, so you can just write the description yourself.	https://marketplace.visualstudio.com/items?itemName=njpwerner.autodocstring
Python style check	VSCode + flake8	It will check if it conforms to pep8 and display the result.	https://pypi.org/project/flake8/
Python automatic format	VSCode + autopep8	To some extent, it will automatically modify the code to be pep8 compliant. For example, open two blank lines above the class definition, or put a space in the argument.	https://pypi.org/project/autopep8/

In code development, DB is used in many cases.
I will introduce a convenient tool that can generate ER diagram, table definition, and DDL with GUI.
ERMaster, a plug-in for Eclipse.
If you write an ER diagram with GUI, you can generate Excel table specifications and DDL statements from it.
I think it is better to write the conceptual data model in PowerPoint or draw.io, and write it in ERMaster from the logical data model.

Use	Tool name	Explanation	Link
ER diagram, table definition, DDL generation	ERMaster	Eclipseのプラグインで、GUIで、ER diagram, table definition, DDL generationができます。	http://ermaster.sourceforge.net/index_ja.html