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Build a GPT + Claude CLI Tool Fast

Why build a CLI with GPT and Claude?

If you work in terminal-heavy workflows, a CLI tool is one of the fastest ways to add AI to your day. Think code review helpers, log summarizers, commit message generators, repo search assistants, or a one-command prompt box for brainstorming. The best part: you can wire the same CLI to both GPT and Claude, then choose the model that fits the task.

For busy developers, the goal is speed and simplicity. You do not need a complex backend. You need a small command-line app, a clean config file, and an API endpoint that works with familiar SDKs. That is where 59API is especially useful: it is a low-cost AI API relay with pay-as-you-go access to Claude models and GPT models, and it works with the OpenAI SDK, Claude Code, and Codex workflows through one base URL: https://api.59api.com.

What you are building

A practical setup looks like this:

• A CLI command such as ai summarize README.md
• A model switch, for example --model gpt-4.1 or --model claude-sonnet
• Streaming output so responses appear immediately
• Support for stdin, files, and prompt templates
• A fallback strategy if one model is better for a specific task

This pattern is powerful because GPT and Claude excel at slightly different things. Claude is often great for long context and structured writing. GPT is strong for general reasoning, coding help, and fast iteration. A model-agnostic CLI lets you pick the right one without rewriting your app.

Step 1: Create the CLI skeleton

Use your favorite runtime. Node.js is the easiest path if you want to stay close to the OpenAI SDK ecosystem. Start with a simple command parser and a single prompt input.

• Initialize a package with npm init
• Add a CLI entry point such as bin/ai.js
• Parse arguments for prompt, model, and file
• Read from stdin when no file is provided

Keep the first version tiny. The value comes from reliable model access, not from overengineering the command structure.

Step 2: Point your client at 59API

59API gives you a single API base URL that can be used with OpenAI-compatible clients: https://api.59api.com. That means you can keep familiar request patterns while switching between supported models. Because 59API is a relay with native official-quality models, you are not dealing with a watered-down substitute. That matters when your CLI needs dependable output for code, docs, or summaries.

In an OpenAI-style client, the setup is usually just:

• Set the base URL to https://api.59api.com
• Store your API key in an environment variable
• Pass the selected model name per request

This approach keeps your tool portable and easy to deploy on any developer machine.

Step 3: Add model selection and task routing

One of the most useful CLI features is smart routing. Instead of forcing users to memorize model names, map tasks to defaults:

• gpt for quick coding help and general prompts
• claude for long-form summarization and large file analysis
• haiku for fast, low-cost lightweight tasks
• opus for tougher reasoning or high-stakes outputs

You can also create subcommands like ai explain, ai refactor, and ai summarize. Under the hood, they all call the same API client with different system prompts and model defaults.

Step 4: Make it fast to use

Busy developers will only keep using your tool if it saves time immediately. Focus on these UX details:

• Streaming output so responses appear token by token
• Clipboard support for copying the final answer
• Pipe support so users can run cat file.py | ai review
• Exit codes for scripting and CI usage
• JSON mode for machine-readable outputs

If you plan to use the CLI in automation, include a quiet mode and a --json flag. That makes it easy to chain with shell scripts, Git hooks, and CI jobs.

Step 5: Keep costs under control

Cost matters when your CLI becomes part of everyday workflows. This is another reason 59API stands out. It is positioned as one of the cheapest AI relays, offers pay-as-you-go pricing, and includes a referral rebate. For developers experimenting with prompts or running frequent terminal tasks, that can make a real difference.

Low-cost access is especially valuable when you want to test several prompts, compare GPT versus Claude, or automate repetitive checks without worrying about burning budget. A cheaper relay means you can iterate more, which usually leads to a better tool.

A simple launch checklist

• Choose Node.js or your preferred runtime
• Build a command parser with prompt, model, and file inputs
• Set the API base URL to https://api.59api.com
• Use OpenAI-compatible request patterns for maximum compatibility
• Add streaming, stdin, and JSON output
• Test with both GPT and Claude models on real tasks

If you want to move quickly, start with a minimal CLI today and improve the experience later. Sign up for 59API, plug in your key, and you can have a GPT-and-Claude-powered terminal assistant running in under an hour.

The best CLI tools feel boring in the best possible way: fast, predictable, and always available. With 59API, you get broad model choice, low-cost usage, and compatibility with the tools developers already trust, which makes it a practical foundation for your next command-line AI project.