Built-in Commands

Fellow includes a variety of built-in commands that can be used out of the box. Each command defines structured inputs and behavior, allowing the AI agent to perform useful operations like editing files, navigating code, or running tests.

Below is a complete reference of all available built-in commands.

Table of Contents

create_file

Creates an empty file at the given path. If the file already exists, it is left unchanged.

Input fields:

  • filepath (str) – The path of the file to create.

view_file

Displays the content of a file, optionally between two line numbers.

Input fields:

  • filepath (str) – Path to the file
  • from_line (int, optional) – Start line (1-based)
  • to_line (int, optional) – End line (inclusive)

delete_file

Deletes a file. Directories are not allowed.

This command is not included in the default command list for safety reasons, but you can easily enable it by adding it to your config file:

commands:
  - delete_file

Input fields:

  • filepath (str) – Path to the file

edit_file

Overwrites the content of a file with the given text.

Input fields:

  • filepath (str) – File path to edit
  • new_text (str) – Replacement content

list_files

Recursively lists files and directories starting from a given directory.

Input fields:

  • directory (str) – Start directory
  • max_depth (int) – Max recursion depth (1 = non-recursive)
  • pattern (str, optional) – Filter by filename substring

run_python

Executes a Python script in a subprocess and captures stdout/stderr.

Input fields:

  • filepath (str) – Path to .py script
  • args (str, optional) – Command-line arguments

run_pytest

Runs pytest on the specified target and returns output.

Input fields:

  • target (str) – File or folder to test
  • args (str, optional) – Extra pytest flags (e.g., -k test_name)

list_definitions

Extracts function and class signatures from a Python file.

Input fields:

  • filepath (str) – Python file to analyze

Output:

  • Function and class names with argument signatures and docstrings

get_code

Extracts the source code of a specific class, function, or method.

Input fields:

  • filepath (str) – Python file path
  • element (str) – Name like my_func or MyClass.my_method

make_plan

Passes a plan string to the currently active AI client via its set_plan method.
It is up to the specific client implementation to decide how the plan is stored, used, or persisted.

For details on how plans are handled, see:

Input fields:

  • plan (str) – A multi-step plan to guide the assistant’s reasoning

pip_install

Installs a Python package using pip. Optionally specify a version.

Input fields:

  • package_name (str) – Package to install
  • version (str, optional) – e.g., 1.2.3

search_files

Performs a case-insensitive search for a string in a directory tree.

Input fields:

  • directory (str) – Root directory
  • search (str) – String to look for
  • extension (str, optional) – Restrict to files with this extension

summarize_file

Uses the current AI client to summarize the contents of a text file.

Input fields:

  • filepath (str) – File to summarize
  • max_chars (int, optional) – Limit characters to read