Butterfish

What is Butterfish?

Butterfish is an MIT-licensed command-line tool that wraps your existing bash or zsh session with AI help. After you run butterfish shell, you work as normal, and any line that starts with a capital letter is sent to a language model instead of being executed. Because the model sees your recent shell history and output, you can ask why the last command failed or request a command that fixes it, with no copying between windows. It also suggests commands as you type, which you accept with Tab, and offers a Goal Mode that acts as an agent: begin a line with an exclamation mark to have it propose commands, run them and debug the results. Prompts are stored in an editable file and verbose logging shows the raw requests. It defaults to OpenAI models, can point at any OpenAI-compatible server, and runs on macOS and Linux.

Use cases

• Ask why a shell command failed
• Generate commands from a plain-English request
• Autocomplete commands with AI suggestions
• Debug a build with Goal Mode
• Summarize terminal output
• Run a local model from the command line

Who it's for

• Command-line users
• Developers
• System administrators

Why use Butterfish

• The model reads your shell history, so you do not paste errors into a separate chat window.
• Only lines that start with a capital letter go to the AI, so your normal commands behave as before.
• Prompt wrappers are visible and editable, so you can see and control what text is sent to the model.
• Pointing it at any OpenAI-compatible server lets you use a local model instead of a hosted one.
• The software is free under the MIT license, so the only cost is your model provider's usage.

Butterfish features

• AI prompting inside bash and zsh sessions
• Shell history and output included as context
• Capital-letter prompts that leave normal commands untouched
• Command autosuggest accepted with Tab
• Goal Mode agent started with an exclamation mark
• Unsafe Goal Mode that runs commands without confirmation
• Editable prompt templates in a YAML file
• Verbose mode that logs raw AI requests and responses
• Model selection and custom base URL for compatible APIs
• Extra commands for prompting, summarizing and managing embeddings

Butterfish integrations

• OpenAI
• Homebrew
• Go
• bash
• zsh

How to get started with Butterfish

1. Install Butterfish with Homebrew on macOS or with go install.
2. Run butterfish shell to start a wrapped bash or zsh session.
3. Paste your OpenAI API key on the first run, which is saved to a local config file.
4. Work as usual and start a line with a capital letter to ask the AI a question.
5. Start a line with an exclamation mark to let Goal Mode propose and run commands toward a goal.

Butterfish limitations

• Needs an OpenAI API key or an OpenAI-compatible server, and that provider bills the usage
• Supports macOS and Linux only
• Goal Mode is described by the author as hit or miss, and succeeds more often on simple goals
• Unsafe Goal Mode runs commands without asking and can be dangerous

Butterfish pricing

Butterfish is open source, so you can use and self-host it for free.

Prices can change and may vary by country or exclude tax. Check the official pricing page.

Butterfish alternatives

The main Butterfish alternatives listed on Debuly are Warp, Aider, TmuxAI, Lacy Shell, GoCodeo and AI2SQL. The table compares pricing and platforms; order is A–Z.

1. 

   AI2SQL

   AI SQL assistant that turns plain-English requests into queries, explains and fixes SQL, and can run read-only queries on your own database.

   CodingProductivityDeveloper platforms
   FreemiumVisit AI2SQL (official site)
2. Ai

   Aider

   Open-source AI pair programming tool that runs in your terminal and edits code in your local git repository using the LLM you choose.

   CodingDeveloper platforms
   Open sourceVisit Aider (official site)
3. 

   GoCodeo

   AI coding agent for VS Code that builds apps, answers code questions and generates tests, with a free plan and paid tiers from $9 a month.

   CodingDeveloper platformsAutomation and agents
   FreemiumVisit GoCodeo (official site)
4. 

   Lacy Shell

   Free MIT-licensed ZSH and Bash plugin that runs shell commands normally and sends plain-English questions to the AI CLI you choose.

   Developer platformsCodingProductivity
   Open sourceVisit Lacy Shell (official site)
5. 

   TmuxAI

   Open-source AI terminal assistant that reads all your tmux panes and runs approved commands in a separate pane.

   CodingAutomation and agentsDeveloper platforms
   Open sourceVisit TmuxAI (official site)
6. 

   Warp

   Terminal with a built-in coding agent, shared team workspace and cloud agents, plus factory-as-code for automating software work.

   CodingDeveloper platformsAutomation and agents
   FreemiumVisit Warp (official site)

Butterfish FAQ

Sources & verification

Facts on this page come from the official sources below, each with the date we read it. Written by Debuly; the vendor did not review this page.

Image credits

• Logo: from butterfi.sh · fetched 23 Oct 2026 · Vendor trademark, used only to identify the product; removed on request
• Cover: none collected yet, so a generated tile is shown.

Spot an error? Report an issue with this listing. We also remove a logo or image on the owner's request.