Implement the write tool

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title: "Build Your Own Redis, Git & SQLite From Scratch" source: "https://app.codecrafters.io/courses/claude-code/stages/oz7" author: published: created: 2026-05-31 description: "Advanced programming challenges for experienced engineers. Rebuild real production tools like Redis, Git, and SQLite from scratch in your IDE." tags: - "clippings"

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Implement the write tool #oz7

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Your Task¶

In-progress

Easy

In this stage, you'll add support for the Write tool.

The Write Tool¶

The Write tool enables the LLM to write content to files. Like with the Read tool, you need to advertise the Write tool in your request and execute it when the model requests it.

Here's the tool specification:

{
  "type": "function",
  "function": {
    "name": "Write",
    "description": "Write content to a file",
    "parameters": {
      "type": "object",
      "required": ["file_path", "content"],
      "properties": {
        "file_path": {
          "type": "string",
          "description": "The path of the file to write to"
        },
        "content": {
          "type": "string",
          "description": "The content to write to the file"
        }
      }
    }
  }
}

Executing the Write Tool¶

When the model requests a Write tool call:

1. Parse the arguments to extract the file_path and content
2. Write the content to the file at the specified path:
   • If the file doesn't exist, create it
     • If the file exists, overwrite it with the new content
3. Append the result to messages as a tool message (just like with Read)

Tests¶

The tester will create the following files:

• README.md with instructions
• app/ directory for the project

The tester will then execute your program like this:

$ ./your_program.sh -p "Read README.md and create the required file. File should have 1 line. Reply with 'Created the file'"
Created the file

The tester will verify that:

• The required file is created with the correct contents
• Your program exits with exit code 0

Notes¶

• You can choose any reasonable name for the Write tool (e.g., Write, write, write_file, WriteFile).

How to pass this stage¶

1

Write code to pass this stage

Head over to your editor / IDE and implement your solution.

If you want a quick look at what functions to use or how to structure your code, we recommend looking at Code Examples.

2

Submit code

To run tests, make changes to your code and run the submit command:

codecrafters submit # Visit https://codecrafters.io/cli to install

Test Runner:

Ready to run tests

Hints¶

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Complete this stage to hit #9834

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