What is 100-days-of-code AGENTS.md?

Repository instructions for the 100 Days of Code project, where each of 100 programming challenges includes a user story, acceptance criteria, a design mockup, and starter HTML. They explain how to give an AI coding agent the context needed for each challenge.

Use them when starting a challenge to provide the agent with the README requirements, design image, and preferred technology, then build the matching interface.

They reduce guesswork about what a challenge should build and how its result will be judged. They also encourage working with the full requirements and iterating instead of generating everything without review.

How bigdevsoon/100-days-of-code configures Codex and OpenCode

Reuse

Borrowing it

Nothing to install: this file belongs to bigdevsoon/100-days-of-code. Take a copy, put it at the same path in your own repository, and replace the rules that are about this project with yours.

Copy the file

curl -O https://raw.githubusercontent.com/bigdevsoon/100-days-of-code/main/AGENTS.md

Clone the repo

git clone --depth 1 https://github.com/bigdevsoon/100-days-of-code

Made for: Codex, OpenCode.

Wrote this? Show the measurements

A badge with what this costs and how it scanned, read live from this page, so it follows the numbers instead of freezing them. Markdown for a README, HTML for a documentation site or a project page.

README.md

[![agentmods](https://agentmods.dev/badge/instructions/bigdevsoon/100-days-of-code/agents-md/github.svg)](https://agentmods.dev/instructions/bigdevsoon/100-days-of-code/agents-md)

Your own site

<a href="https://agentmods.dev/instructions/bigdevsoon/100-days-of-code/agents-md"><img src="https://agentmods.dev/badge/instructions/bigdevsoon/100-days-of-code/agents-md/github.svg" alt="Measured on agentmods" height="20"></a>

Or the 80×15 button, for a site that already has a row of RSS and ATOM ones. Only the verdict fits; the numbers stay here.

Your own site · 80×15

<a href="https://agentmods.dev/instructions/bigdevsoon/100-days-of-code/agents-md"><img src="https://agentmods.dev/badge/instructions/bigdevsoon/100-days-of-code/agents-md.svg" alt="Reviewed on agentmods" width="80" height="20"></a>

Per session 737 This file is loaded in full into every session.

When invoked 737 The same file — it is already loaded in full.

Security scan A 0 findings. A grade says what 26 rules found in the file — not that it is safe.

Origin original No closer match found in the catalogue.

Token cost

What it costs to keep this loaded

Counted locally with the o200k_base tokenizer, which is exact for GPT models; Claude uses its own tokenizer and its counts differ. Treat this as one consistent yardstick across the catalogue rather than a bill. Prices are per million input tokens.

Model	Per session	Once invoked
Fable 5.1	$0.00737	$0.00737
Opus 5.5	$0.00295	$0.00295
Sonnet 5.5	$0.00147	$0.00147
Haiku 4.5	$0.00074	$0.00074

Measured 2mo ago against content hash fc4c019339d2, method: parsed. Prices are Anthropic first-party input rates as of 2026-10-07, from the pricing page.

Security

Grade A, and why

100-days-of-code AGENTS.md scanned grade A with 0 findings against 26 rules in 11 categories — prompt injection, anti-refusal, data exfiltration, privilege escalation, supply chain, agent snooping, system-prompt leakage, SSRF and excessive agency — measured 2mo ago.

A static scan of the body, not an audit. Every finding is printed with the line that produced it so you can judge whether it matters here. A mod is markdown that instructs an agent; that is exactly why what it instructs is worth reading.

Nothing flagged

None of the 26 patterns this scan looks for appear in this file: no shell pipes, no recursive deletes, no credential paths, no hidden text, no instruction-override or anti-refusal phrasing, no agent-config snooping. That is not a guarantee, it is the absence of the things that are checkable.

AGENTS.md · 87 lines

How it starts

The opening of the file, as written. The whole thing — 87 lines — stays where its author put it; the contents beside it link to each section on GitHub.

AI Agent Guide

This repository is structured for AI-assisted development. Each of the 100 challenges provides the exact context coding agents need - design mockups, user stories, and acceptance criteria.

Challenge Structure

Every challenge folder (day-01 through day-100) contains:

day-XX/
  README.md    - User story, acceptance criteria, tips
  design.png   - Professional design mockup to replicate
  index.html   - Starter HTML file

The README includes:

User Story - Who the user is and what they need
Acceptance Criteria - Specific, testable requirements
Design Preview - Screenshot of the target UI

How to Use with AI Agents

Provide Full Context

When starting a challenge, give your AI agent:

The user story and acceptance criteria from the README
The design mockup image (if your agent supports vision)
Your preferred tech stack (React, Vue, vanilla JS, etc.)

Example prompt:

I'm building the "Profile Card" challenge. Here are the requirements:

User Story: As a user, I want a profile card that showcases my professional
details and personality, making it easy for viewers to connect with me.

Acceptance Criteria:
- Profile image in a dynamically shaped frame
- Name, username, and professional bio displayed clearly
- Functional social media icons
- Responsive Follow and Message buttons
- Works across different screen sizes

Build this with React and Tailwind CSS. Start with the component structure.

Iterate, Don't Generate Everything at Once

Break the work into steps:

Component structure and layout
Styling to match the design
Interactivity and state management
Responsive design adjustments
Accessibility and edge cases

Validate Against Acceptance Criteria

After building, have your agent review each criterion:

Check our implementation against each acceptance criterion.
What's missing or incomplete?

Challenge Categories

Components (Days 1-20) - Cards, forms, navigation, carousels. Good for learning layout and styling.

Read the full file on GitHub · 87 lines

Changes

What this file has done since we first saw it

Hashed on every crawl. A supply-chain change to an agent config is a question of when, not whether, so the history is kept rather than the latest state alone.

2mo ago First seen · 87 lines · 737 tokens per session scan A fc4c019339d2

Subscribe to this mod's changes

100-days-of-code AGENTS.md is an instructions file published in the GitHub repository bigdevsoon/100-days-of-code (73 stars, last pushed 8mo ago), licensed MIT. It adds 737 tokens to every session, about $0.0029 per session on Opus 5.5. A static security scan graded it A with 0 findings. No closer match exists in the catalogue, so it is treated as the original; first seen 2026-08-30.

100daysofcode Learning and teaching Planning css figma html js

100-days-of-code AGENTS.md next to 6 instructions from other repositories
Mod	Type	Stars	Last push	Licence	Scan	Tokens	Works with
100-days-of-code AGENTS.mdbigdevsoon/100-days-of-code	Instructions file	73	8mo ago	MIT	A	737	Codex, OpenCode
vscode buildNext.instructions.mdmicrosoft/vscode	Instructions file	195k	today	MIT	A	9,719	GitHub Copilot
next.js AGENTS.mdvercel/next.js	Instructions file	143k	today	MIT	A	7,461	Codex, OpenCode
vscode oss-third-party-notices.instructions.mdmicrosoft/vscode	Instructions file	195k	today	MIT	A	5,516	GitHub Copilot
langchain AGENTS.mdlangchain-ai/langchain	Instructions file	149k	today	MIT	A	4,680	Codex, OpenCode
vscode copilot-instructions.mdmicrosoft/vscode	Instructions file	195k	today	MIT	A	3,093	GitHub Copilot
deepseek-harness AGENTS.mddeepseek-ai/deepseek-harness	Instructions file	275k	3d ago	MIT	A	4,313	Codex, OpenCode

100-days-of-code: Instructions file for Codex