How to Get Started and Build with Gemini CLI (Powered by Gemini 3 Flash)

**By Lesly Zerna / @leslysandra** As developers, we are constantly looking for tools that speed up our workflow without breaking our flow state. Last June 2025, Google made a massive splash in the open-source community by releasing the **Gemini CLI** and in December 2025, by updating with their latest model, **Gemini 3 Flash**. If you are tired of copy-pasting code between your browser and your IDE, or if you want to see what a true "AI Agent" looks like in your terminal, this guide is for you :) *Note: Many of the concepts and examples in this post were inspired by this [Gemini CLI course by DeepLearning.AI](https://www.deeplearning.ai/short-courses/gemini-cli-code-and-create-with-an-open-source-agent/), which I highly recommend checking out, as well as checking the official [Gemini CLI documentation](https://geminicli.com/docs/get-started/installation/) as well as [Google for devs blog](https://blog.google/innovation-and-ai/technology/developers-tools/introducing-gemini-cli-open-source-ai-agent/).* --- ## What is Gemini CLI? In simple terms, **Gemini CLI** is a **terminal application** that lets you chat with Google’s Gemini AI directly from your command line. But it is more than just a chatbot. It is an **open-source AI agent** **powered by Gemini**. When you use ChatGPT or the Gemini web interface, you are in a "sandbox"—the AI cannot see your files or run commands unless you upload them. Gemini CLI breaks that wall. It lives *inside* your environment, meaning it can understand your project structure, read your code directly, and help you build faster. **Why is the "Gemini 3 Flash" update important?** [Gemini 3 Flash](https://developers.googleblog.com/en/gemini-3-flash-is-now-available-in-gemini-cli/) is optimized for speed and low latency. When you are using an AI Agent that needs to perform multiple steps (like "read this file," then "analyze it," then "write a test"), speed is critical. Flash makes the CLI feel snappy and responsive. --- ## Why Use the CLI? (Browser vs. Terminal) Working from the browser is great for general questions, but for building software, the Command Line Interface (CLI) is superior. Here is why: * **Direct File System Access:** You don't need to copy-paste code. You can simply say, "Refactor the `utils.py` file," and the CLI can read it and propose changes directly. * **Context Awareness:** The CLI knows where it is. It understands your current working directory and the files inside it. * **Automation & Scripting:** You can pipe output from other commands into Gemini. For example: `cat logs.txt | gemini "Find the critical error"`. * **Built-in Tools:** Gemini CLI comes battery-included with tools such as: * **File System:** Read, write, and list files. * **Web:** Fetch URLs and search Google (grounding your code in real-time info). * **Shell:** Execute terminal commands safely. * **Customization & Extensions:** Because it is **open source**, you can extend it. It supports the **Model Context Protocol (MCP)**, allowing you to build custom tools that connect to your database or internal APIs. --- ## Real-Life Examples and Ideas to Build Here are a few ways you can start using Gemini CLI today to boost your productivity. ### 1. The "Smart" Code Reviewer Instead of manually checking your code for style issues, use Gemini CLI to review it before you push. * **Command:** `gemini "Review @main.py for potential bugs and clean code practices. Output the suggestions as a list."` * **Why it works:** The CLI reads the file directly and uses Gemini’s logic to find edge cases you might have missed. ### 2. Instant Data Analyst Imagine you have a messy CSV file or a log file and you need quick insights. * **Scenario:** You have a file called `server_logs.csv`. * **Command:** `gemini "Read @server_logs.csv and tell me which IP address appears the most frequently. Then, use grep to count exactly how many times it appears."` * **Why it works:** The agent combines its ability to write code (to analyze the CSV) with system tools (like `grep`) to verify the data. ### 3. Rapid Prototyping Need to scaffold a new feature? * **Command:** `gemini "Create a new folder called 'blog-app'. Inside it, create an index.html file with a basic responsive layout and a style.css file with a dark mode theme."` * **Result:** The CLI actually creates the folder and writes the files for you. You are ready to start coding immediately. --- ## How to Get Started: Installation Ready to try it? Installing Gemini CLI is straightforward. You will need `Node.js` installed on your machine. *([More details, see the official documentation at geminicli.com](https://geminicli.com/docs/get-started/installation/))* **Step 1: Open your terminal.** **Step 2: Run the install command.** ```bash npm install -g @google/gemini-cli@latest ``` **Step 3: Authenticate.** You can start the tool by simply typing: ```bash gemini ``` On your first run, it will ask you to authenticate. You can usually log in directly with your Google account, which gives you a generous free tier to start experimenting.  And once it is installed you can see it running in your terminal:  **Step 4: Enable the Latest Features (Crucial Step!)** To use the powerful **Gemini 3 Flash** model, you need to enable preview features. 1. Type `/settings` in the CLI. 2. Look for **"Preview Features"**. 3. Set this to **"True"**. This ensures you are running on the latest, fastest, and most capable models available.  --- ## Under the Hood: How Gemini CLI Works You might be wondering, "How does a text box in my terminal know how to run code?" Gemini CLI uses a concept called the **ReAct Loop** (Reason + Act). Here is the simple [explanation](https://docs.cloud.google.com/gemini/docs/codeassist/gemini-cli) of what happens when you type a command: 1. **Thought:** You ask a question (e.g., "Why is my build failing?"). The AI analyzes your request. 2. **Tool Use:** Instead of just guessing, the AI sees it has "tools" available—like reading a file or running a shell command. It decides, "I should run the build command to see the error." 3. **Observation:** The CLI runs the command, captures the output (the error message), and feeds it back to the AI. 4. **Answer:** The AI reads the error and gives you the specific fix. This "Loop" allows the CLI to act like a real pair programmer rather than just a text generator. --- ## Navigating the Terminal: Essential Commands ## Once you have installed Gemini CLI, you aren't just typing into a void. There are specific commands to help you control the agent. * **/help**: The most important command. Use this to see what the agent can do and how to interact with it. * **/settings**: Use this to explore your setup. This is where you configure your **Assistant** settings and change the **Mode**. * **/docs**: Opens the documentation if you need to read up on advanced features. ### How to Reference Your Files This is the superpower of the CLI. You don't need to copy-paste code. To ask Gemini about a specific file, simply use the `@` symbol. **Example:** > "Can you explain the logic inside **@main.py** and suggest improvements?" The agent will read that specific file and base its answer on the code inside it. --- ## Understanding Context and `GEMINI.md` **What is Context?** Context is simply a collection of information that the AI agent uses to understand your specific request. It’s the "background knowledge" the AI needs so you don't have to repeat yourself. ### The Magic of `GEMINI.md` You can teach the CLI about your project by creating a special file called `GEMINI.md`. Think of this as a "ReadMe for the AI." If you place a `GEMINI.md` file in your folder, the CLI automatically reads it to understand your project rules, coding style, or architecture. You can place this file in: 1. **The Global Directory:** For rules that apply to *all* your projects. 2. **The Current Working Folder:** For project-specific rules. 3. **Subdirectories:** For rules specific to that module. ### Managing Memory You can verify what the AI currently "knows" or add new things to its memory manually using these commands: * **Check Context:** ```bash /memory show ``` *This will list everything currently in the agent's context.* * **Add Context Manually:** ```bash /memory add "Remember that we are using Python 3.11 for this project" ``` *Or you can point it to a specific context file:* ```bash /memory add path/to/another/gemini.md ``` --- Already excited about the topic? This is just the intro, we'll explore more about CLI Extensions, uses for Software Development, Data Analysis, MCP and more in the coming blogs! --- ## Conclusion (This first part!) The shift from chat-in-browser to agent-in-terminal is a huge leap for developer productivity. With **Gemini 3 Flash** now powering the **Gemini CLI**, and the ability to customize **Context** using `GEMINI.md`, we have a tool that is fast enough to keep up with our thoughts and smart enough to handle complex tasks. Give it a try, explore the **open source** code, and let me know what you build! More blogs coming up soon! Subscribe and stay tuned!, Lesly