# Coding agents and agentic development How coding agents work and how teams build with them, from vibe coding and written specs to MCP and saved session history. Start here ## [What is a coding agent?](https://specstory.com/learning/ai-coding/coding-agent) A coding agent is an AI system that edits files and runs commands in a loop to complete a programming task with little step-by-step direction. 10 min read ## Concepts ### [What is vibe coding?](https://specstory.com/learning/ai-coding/vibe-coding) Vibe coding is building software by describing the result to an AI and accepting the code it writes without reading it, judging it by how the app behaves. ### [What is spec-driven development?](https://specstory.com/learning/ai-coding/spec-driven-development) Spec-driven development is a way of working where a written specification, not a chat prompt, drives what a coding agent builds and how it is checked. ### [What is the Model Context Protocol (MCP)?](https://specstory.com/learning/ai-coding/model-context-protocol) The Model Context Protocol (MCP) is an open standard that lets AI applications connect to tools and data through a common client and server interface. ### [What is AI coding session history?](https://specstory.com/learning/ai-coding/ai-coding-session-history) AI coding session history is the set of saved coding agent transcripts, each holding the prompts, replies, tool calls, and results of one session. ### [What is agentic engineering?](https://specstory.com/learning/ai-coding/agentic-engineering) Agentic engineering is building software with coding agents while keeping engineering practices, from written specs and tests to review and verification. ### [What is AGENTS.md?](https://specstory.com/learning/ai-coding/agents-md) AGENTS.md is a Markdown instruction file in a repository that tells coding agents how to set up, build, test, and change the project. ### [What is an agent harness?](https://specstory.com/learning/ai-coding/agent-harness) An agent harness is the software around a language model that gives it tools, context, memory, and a loop, which turns the model into a working agent. ### [What is context engineering?](https://specstory.com/learning/ai-coding/context-engineering) Context engineering is choosing what a model receives at each step, from instructions and files to tool results and history, so it has what the task needs. ### [What is human-in-the-loop for coding agents?](https://specstory.com/learning/ai-coding/human-in-the-loop) Human-in-the-loop means a person approves, corrects, or reviews an AI agent's work at set points, e.g. before code merges, while the agent does the rest. ## Comparisons ### [What is the difference between agentic coding and vibe coding?](https://specstory.com/learning/ai-coding/agentic-coding-vs-vibe-coding) Agentic coding directs a coding agent with plans, reviews, and checks, while vibe coding accepts the AI's code unread, so they differ in what is verified. ## Terms in this topic **[Agent harness](https://specstory.com/learning/glossary#agent-harness)** An agent harness is the software around a language model that gives it tools, context, memory, and a loop, which turns the model into a working agent. **[Agent loop](https://specstory.com/learning/glossary#agent-loop)** The agent loop is the cycle in which a model requests an action, the harness runs the tool, and the model reads the result. It ends when the model requests no tool, or when a step limit, a time limit, or a person stops it. **[Agent trajectory](https://specstory.com/learning/glossary#agent-trajectory)** An agent trajectory is the ordered sequence of an agent's actions, tool calls, and observations while it works on a task, which is what a transcript records. **[Agentic engineering](https://specstory.com/learning/glossary#agentic-engineering)** Agentic engineering is a way of building software that directs coding agents while keeping engineering practices, from written specs and tests to code review and verification. **[AGENTS.md](https://specstory.com/learning/glossary#agents-md)** AGENTS.md is a Markdown file in a repository that gives coding agents project instructions, e.g. how to build, test, and change the code. **[Coding agent](https://specstory.com/learning/glossary#coding-agent)** A coding agent is an AI system that edits files and runs commands in a loop to complete a programming task with little step-by-step direction. **[Coding agent transcript](https://specstory.com/learning/glossary#coding-agent-transcript)** A coding agent transcript is a saved record that holds a coding session's prompts, replies, tool calls, and results. A collection of saved transcripts is called AI coding session history. **[Context window](https://specstory.com/learning/glossary#context-window)** A context window is the amount of text, measured in tokens, that a language model can take into account at once, including instructions, files, and history. **[Human-in-the-loop](https://specstory.com/learning/glossary#human-in-the-loop)** Human-in-the-loop is a way of running an AI system in which a person approves, corrects, or reviews its work at set points before the work takes effect. **[MCP server](https://specstory.com/learning/glossary#mcp-server)** An MCP server is a program that exposes tools or data to AI agents over the Model Context Protocol, so an agent can call them in a standard way. **[Model Context Protocol (MCP)](https://specstory.com/learning/glossary#model-context-protocol)** The Model Context Protocol is an open standard that lets AI applications connect to tools and data through MCP servers, so an agent can call them in a uniform way. **[Spec-driven development](https://specstory.com/learning/glossary#spec-driven-development)** Spec-driven development is a way of working that writes a specification of what software should do before a coding agent writes it. The spec is then used to guide and check the work. **[Vibe coding](https://specstory.com/learning/glossary#vibe-coding)** Vibe coding is a way of building software in which a person describes the result to an AI and accepts the code without reading it, judging it only by using the app. 13 terms from the [Learning Center glossary](https://specstory.com/learning/glossary). --- Source: [Coding agents and agentic development | SpecStory](https://specstory.com/learning/ai-coding)