harness

A Go library for calling different AI coding agent CLIs (Docker Agent, Claude Code, Pi, Codex) through a unified interface. Switch between agents by changing a single line of code.

Install

go get github.com/rumpl/harness

Quick start

package main

import (
	"context"
	"fmt"

	"github.com/rumpl/harness"
	"github.com/rumpl/harness/dockeragent"
)

func main() {
	// Create a provider — swap this line to switch agents.
	p := dockeragent.New("coder")

	// Run the agent and handle streaming events.
	harness.Run(context.Background(), p, "Explain goroutines", func(ev harness.Event) {
		switch ev.Type {
		case harness.EventText:
			fmt.Print(ev.Text)
		case harness.EventToolCall:
			fmt.Printf("[tool: %s] %s\n", ev.ToolName, ev.ToolArgs)
		case harness.EventResult:
			fmt.Printf("\nResult: %s\n", ev.Result)
		}
	})
}

Switching providers

// Docker Agent
p := dockeragent.New("coder")

// Claude Code
p := claudecode.New("claude-sonnet-4-6", claudecode.WithEffort(claudecode.EffortHigh))

// Pi
p := pi.New("claude-sonnet-4-6")

// Codex
p := codex.New("gpt-5.4-mini")

The rest of your code stays exactly the same — all providers implement harness.Provider.

The Provider interface

type Provider interface {
	Name() string
	PrintCommand(prompt string) string
	InteractiveArgs(prompt string) []string
	ParseStreamLine(line string) []Event
}

Method	Purpose
Name()	Human-readable identifier ("docker-agent", "claude-code", etc.)
PrintCommand()	Shell command for non-interactive mode (sh -c safe)
InteractiveArgs()	Arg list for interactive mode (first element = binary)
ParseStreamLine()	Parse one NDJSON line into []Event

Event types

Type	Fields set
EventText	Text
EventResult	Result, Usage (opt)
EventToolCall	ToolName, ToolArgs

Example CLI

go run ./cmd/harness-example --provider docker-agent --model coder "Hello world"
go run ./cmd/harness-example --provider claude-code --model claude-sonnet-4-6 "Hello world"
go run ./cmd/harness-example --provider pi --model claude-sonnet-4-6 "Hello world"
go run ./cmd/harness-example --provider codex --model gpt-5.4-mini "Hello world"

# Just print the command without executing:
go run ./cmd/harness-example --print-cmd --provider docker-agent --model coder "test"

License

MIT