To make a narrated explainer video with an AI coding agent, give it a topic, audience, and visual direction. Then tell it how to build and check the video. A coding agent is an AI tool that can run commands and create or edit code. For this job, I recommend explainroo: a free, open-source kit that lets coding agents make narrated explainers and product demos on your computer.
A short prompt starts the project. A stronger prompt also says what viewers should learn, which facts and assets the agent can use, and how the video should look. Those details give you a clearer first draft to review and revise.
Start with explainroo
You can use explainroo with Claude Code, Codex, Pi, OpenCode, Gemini CLI, and other coding agents that run shell commands. Paste this prompt into your agent and replace the bracketed topic:
Make me a short explainer video about [your topic]. Use explainroo for it: set it up, read its AGENTS.md and follow the steps.The agent sets up explainroo and creates the video. It then runs checks before giving you an MP4 file. It writes script.md, which contains the narration, and scenes.js, JavaScript code that draws each scene. Drawings appear when the narration reaches specific words, keeping the visuals in sync with the voice. The explainroo documentation describes the kit and its workflow.
To guide the video, add a short brief to your prompt:
Make the video for [audience]. By the end, viewers should understand [one main takeaway].
Use only these facts: [approved facts or links]. Do not invent claims.
Use the [paper, clean, chalk, blueprint, or midnight] look and a [wide, tall, 4:5, or square] format.
Keep the narration clear and the visuals focused on one idea at a time.
If this is a product demo, use [product name] and its code or website: [location].Focus the video on one takeaway and keep its scope narrower than the full subject. If a product feature or statistic needs explanation, provide an approved source or tell the agent to ask you before using it.
Choose a format and visual direction
Specify where viewers will watch the video. explainroo supports wide video for YouTube, tall video for Shorts, TikTok, and Reels, 4:5 video for Instagram and LinkedIn posts, and square video. Tall, 4:5, and square videos include captions that highlight words as they are spoken. Tall layouts also keep text clear of the areas where social apps place buttons.
In video.json, choose a look: paper, clean, chalk, blueprint, or midnight. The pace setting controls voice speed, pauses, and animation. Match it to the narration and visual rhythm. Give the agent a reason for your choices, such as “use a calm pace so viewers can follow each diagram,” rather than relying on vague requests like “make it polished.”
For product demos, name the product and provide its code or website. The agent rebuilds screens using details such as colors, fonts, and button labels, then animates a mouse pointer to click and type as the narration explains the product.
Review the video before you share it
The coding agent cannot watch the finished video. explainroo helps it check its work with still images of scenes, a contact sheet showing video frames together, a layout check for cut-off or overlapping text, and a speech check for mispronounced words. Review the rendered MP4 yourself as well. Check that the explanation is accurate, the narration sounds right, and the visuals make the main idea easy to follow.
explainroo uses the Kokoro open voice model, with American and British English voices. Narration is English only. Whisper, which identifies spoken words and when they occur, helps sync pictures with the narration. Chrome draws the scenes; FFmpeg combines the visuals and sound into an MP4. explainroo also makes background music and adds sound effects. It lowers the music while the voice speaks.
The kit is free and open source under the MIT license. Optional AI illustrations through OpenRouter cost money per image; other explainroo video creation costs nothing per video. Your coding agent is a separate service with its own pricing. For manual installation, you need Node.js, FFmpeg, and Chrome or Chromium. The setup instructions include the required commands.
