# Harrison Chase's spectrum: the more agentic it is, the more you'll want to watch it

**In June 2024, LangChain's Harrison Chase opened a new series with a deceptively small question — “What is an agent?” — and answered it with a technical definition and a spectrum of “agentic” behavior. The more of that spectrum a system occupies, he argues, the more you need to be able to see inside it while it runs.**

## What the post argues

Chase's own definition, offered with a caveat that it's more technical, and broader, than most people's idea of an agent:

> “An agent is a system that uses an LLM to decide the control flow of an application.”

Control flow just means which step a program runs next. He immediately admits the definition is imperfect — a simple system where an LLM routes between two paths counts as an agent by his definition but wouldn't match most people's intuition of “agent.” Rather than fight over the label, he takes up a suggestion from Andrew Ng, whose tweet he quotes and credits directly: “rather than arguing over which work to include or exclude as being a true agent, we can acknowledge that there are different degrees to which systems can be agentic.” Chase's own comment on it: “I really agree with this viewpoint and I think Andrew expressed it nicely.” From there: a system is more “agentic” the more an LLM decides how it behaves, from a fixed router up through a state machine to a fully autonomous agent that builds and remembers its own tools. His practical argument follows from that spectrum — the more agentic a system is, the more certain kinds of infrastructure matter, observability chief among them:

> “You’ll want the ability to observe what is going on inside, since the exact steps taken may not be known ahead of time.”

He extends that into an argument for intervening, not just watching: you'll also want the ability to modify the state or instructions of a running agent at a particular point, to nudge it back on track if it's drifting from the intended path. Chase doesn't mention MarsDawn anywhere in this post, and doesn't recommend any Markdown tool.

## Our reading, not Chase's

Chase is writing about tooling for people building agent frameworks — LangGraph and LangSmith, by name — not about a person reading a finished document. But his spectrum gives a useful way to size up what you're about to read before you start: the more agentic the system that produced a file, the less you should expect its steps to be predictable from the prompt alone, and the more the file in front of you is worth treating as a record of what actually happened rather than what was supposed to happen. His “observe what is going on inside” is about a running system's internals — traces (a recorded log of everything the agent did during one run), intermediate steps, tool calls — not about reading a Markdown plan after the fact. But the underlying reason he gives, that the exact steps taken may not be known ahead of time, applies just as well to the document an agent hands you when it's done: if the steps weren't predictable going in, the report coming out is the only place left to check them.

## Where MarsDawn helps, and where it doesn't

MarsDawn doesn't observe a running agent's internals — it has no AI model inside and no connection to whatever framework produced the file, so it can't tell you where on Chase's spectrum a given agent sat. It works on the document that lands afterward: the Outline tab (View ▸ Show Sidebar, ⌃⌘S) for a long report's shape, the source and rendered preview side by side (⌘2) for diagrams and math, and live reload that keeps your place when the agent rewrites the file, as long as you have no unsaved edits of your own — the file-level version of watching something that's still moving. Edit ▸ Copy Reference (⌥⌘C) and Copy for AI (⌃⌥⌘C) let you point at exactly where a step went off track, which is the document equivalent of nudging a running agent back on course.

## Try it

MarsDawn is on the Mac App Store. The free `marsdawn` command-line tool works today:

```
brew install redtear1115/tap/marsdawn
```

It exports Markdown to PDF without the app.

[Command Line](/cli/) · Know before you buy: [What MarsDawn doesn't do](/limits/)

## Next

- This series' fuller treatment of transparency and checkpoints: [Anthropic says agents should be transparent — so who reads what they lay out?](/agent-transparency/)
- LangChain's 2026 post at this same address, with an almost identical definition: [Jess Ou's evals pipeline, and the one step in it that's still yours](/reading-notes/langchain-what-is-an-agent/)
- Back to the series: [Editor's reading notes](/reading-notes/)

## Sources

- Harrison Chase, “What is an agent?,” LangChain, June 28, 2024, archived copy: [http://web.archive.org/web/20240724003401/https://blog.langchain.dev/what-is-an-agent/](http://web.archive.org/web/20240724003401/https://blog.langchain.dev/what-is-an-agent/) (fetched and quoted 2026-09-26 via the Wayback Machine; the original address now shows a 2026 article by Jess Ou).

## More

- [MarsDawn](https://marsdawn.southern-light.dev/index.md): Read and review the Markdown your agent wrote, natively on Mac: live split preview, Mermaid, KaTeX, Quick Look, PDF export. Free to try, USD 4.99 once.
- [Features](https://marsdawn.southern-light.dev/features/index.md): A native Mac Markdown editor: live preview, Mermaid and math, themes, plus clean PDF and print pages for meetings, margin notes and paper records.
- [Your writing stays on your Mac](https://marsdawn.southern-light.dev/yours/index.md): MarsDawn has no account, no sync and no cloud. Your Markdown documents stay on your Mac, in the files and folders you choose.
- [Try free, pay once](https://marsdawn.southern-light.dev/pay-once/index.md): MarsDawn is free to download. Try everything for 14 days, then unlock it once for USD 4.99. No subscription, no account.
- [PDF export](https://marsdawn.southern-light.dev/pdf/index.md): Export Markdown as a PDF or print it on your Mac, with Mermaid diagrams and highlighted code. Page breaks avoid splitting short code blocks.
- [A Mac app](https://marsdawn.southern-light.dev/native/index.md): A Markdown editor that is a real Mac app: native windows and tabs, autosave, version history, Quick Look in Finder and a text editor that behaves like a Mac.
- [What MarsDawn doesn't do](https://marsdawn.southern-light.dev/limits/index.md): No sync, no editing on iPhone or iPad, no plugins, no accounts. Themes, but no custom CSS. Know before you buy.
- [Support](https://marsdawn.southern-light.dev/support/index.md): Get help with MarsDawn, the Markdown editor for macOS.
- [Privacy Policy](https://marsdawn.southern-light.dev/privacy/index.md): MarsDawn does not collect personal data. Your documents and settings stay on your Mac.
- [How to open .md files on Mac](https://marsdawn.southern-light.dev/view-markdown-on-mac/index.md): How to open a .md file on a Mac: double-click, set a default app, preview in Finder. For .md files an AI agent wrote, read them rendered in MarsDawn.
- [Mermaid preview on Mac](https://marsdawn.southern-light.dev/mermaid-preview-mac/index.md): See Mermaid diagrams drawn next to your Markdown on a Mac: live preview, Quick Look and PDF export. A broken diagram shows its error and the line.
- [Quick Look for Markdown](https://marsdawn.southern-light.dev/quicklook/index.md): MarsDawn's Quick Look renders Markdown in Finder when you press Space, with Mermaid, KaTeX and highlighted code. It keeps working after the trial ends.
- [Markdown to PDF](https://marsdawn.southern-light.dev/markdown-to-pdf/index.md): Convert Markdown to PDF on a Mac with the free marsdawn command-line tool. Install it with Homebrew and run one command: tables, math, Mermaid and code.
- [MarsDawn compared: VS Code preview, Obsidian, QLMarkdown, LynxOffice](https://marsdawn.southern-light.dev/vs/index.md): For anyone choosing how to read and review Markdown on a Mac, often what an agent wrote. Every cell below comes from the vendor's own pages or our own check, all on 16 October 2026; products change, so a cell can go stale. If you spot a mistake, write to the address on Support.
- [MacMD Viewer vs. MarsDawn](https://marsdawn.southern-light.dev/vs/macmd-viewer/index.md): MacMD Viewer is a read-only Markdown viewer for USD 19.99. MarsDawn edits and previews side by side: free for 14 days, then USD 4.99 once.
- [Best Markdown viewer for Mac (2026)](https://marsdawn.southern-light.dev/best-markdown-viewer-mac/index.md): Eight Markdown viewers for Mac compared by price, Mermaid, math, PDF, live reload, Quick Look and native vs Electron, with who each one suits.
- [Command Line](https://marsdawn.southern-light.dev/cli/index.md): The free marsdawn command-line tool for Mac: export Markdown to PDF from a shell, a script or an LLM agent, with JSON output. Install it with Homebrew.
- [marsdawn for agents](https://marsdawn.southern-light.dev/cli/agents/index.md): A reference for AI agents and scripts that call marsdawn to turn Markdown into PDF: commands, JSON output, schemas, exit codes and requirements.
- [Agent skill](https://marsdawn.southern-light.dev/cli/skill/index.md): One file your coding agent loads to open Markdown it wrote in MarsDawn for your review, and to install marsdawn, export Markdown to PDF and read the JSON result.
- [MCP server](https://marsdawn.southern-light.dev/cli/mcp/index.md): marsdawn has no AI model of its own, so it doesn't matter which agent wrote the Markdown. Call it from the CLI, a skill file, or the marsdawn-mcp MCP server: all three run the same export.
- [Token-efficient review](https://marsdawn.southern-light.dev/token-efficient-review/index.md): A person reviews the rendered page in MarsDawn, never read back into the agent's context. The tool call itself returns a compact JSON result, not the rendered content, so calling it is cheap too.
- [Viewing Markdown elsewhere vs. MarsDawn](https://marsdawn.southern-light.dev/vs/markdown-preview-tools/index.md): How MarsDawn compares to reading Markdown in VS Code's built-in preview, a browser extension, or Claude Desktop's file preview: what each renders, and what it takes to open one file.
- [Themes](https://marsdawn.southern-light.dev/themes/index.md): Four built-in preview themes, each light and dark, plus a curated gallery you open from Settings in MarsDawn for Mac. Quick Look uses your theme.
- [Build a theme](https://marsdawn.southern-light.dev/themes/new/index.md): Pick colours and a handful of style options, see them applied to a sample document live, and submit your theme as a GitHub issue. No install, no git.
- [Make a theme with your agent](https://marsdawn.southern-light.dev/themes/agents/index.md): MarsDawn theme reference for AI agents: each theme.json field with type and range, the CLI loop that checks and renders it, a hand-off link, and how to submit.
- [Theme gallery](https://marsdawn.southern-light.dev/themes/gallery/index.md): Browse preview themes for MarsDawn, each reviewed by the developer, filter them by scenario, and report a problem with one. Build your own in the browser.
- [Sharing exported PDFs](https://marsdawn.southern-light.dev/sharing-exported-pdfs/index.md): Export an agent's Markdown to PDF and hand it to a colleague who doesn't read Markdown and won't install anything. No syntax, no app and no account needed to open it.
- [Why AI output still needs a human reader](https://marsdawn.southern-light.dev/reviewing-ai-output/index.md): AI-written Markdown still has to be understood by a person, not trusted on sight. MarsDawn pairs the rendered page with the source, and draws Mermaid diagrams and KaTeX math, so structure is legible at a glance.
- [Reading what your agent hands back](https://marsdawn.southern-light.dev/reading-agent-output/index.md): AI agents hand back their work as Markdown: plans, specs, progress reports. What people who build agents say about checkpoints and failures, why that output is hard to read, and a five-minute checklist for reviewing a plan.
- [Agent transparency](https://marsdawn.southern-light.dev/agent-transparency/index.md): Anthropic's guide to building agents asks for transparency: show the planning steps. What it says, what it doesn't, and why the steps usually end up as a Markdown file someone has to read.
- [Reviewing an agent plan](https://marsdawn.southern-light.dev/reviewing-agent-plans/index.md): A six-step way to review the plan an AI agent hands you before it runs, in about five minutes and in any editor, with a worked example.
- [Agent design patterns](https://marsdawn.southern-light.dev/agent-design-patterns/index.md): Reflection, tool use, planning and multi-agent collaboration, as Andrew Ng described them, and what each tends to hand back for you to read.
- [Changelog](https://marsdawn.southern-light.dev/changelog/index.md): What changed in each version of the MarsDawn app and the free marsdawn CLI.
- [Roadmap](https://marsdawn.southern-light.dev/roadmap/index.md): What's in progress and what's next for MarsDawn on Mac, iPhone and iPad, by version. No dates, and unscheduled ideas are marked.
- [Editor's reading notes](https://marsdawn.southern-light.dev/reading-notes/index.md): Six short notes on what the people building AI agents actually argue — Anthropic, Chip Huyen, Lilian Weng, Harrison Chase, LangChain and Andrew Ng — and what each one means for the person who has to read what such an agent hands back.
- [Reading notes: Anthropic](https://marsdawn.southern-light.dev/reading-notes/anthropic-building-effective-agents/index.md): Anthropic's December 2024 guide for people building agents separates workflows from agents and describes five workflow patterns, including one where a second LLM call reviews the first. What that means for what lands in your folder.
- [Reading notes: Chip Huyen](https://marsdawn.southern-light.dev/reading-notes/chip-huyen-agents/index.md): Chip Huyen's January 2025 essay on agents splits their actions into read-only and write actions. Why that split is a fast way to spot the line in a plan worth a closer look before you approve it.
- [Reading notes: Lilian Weng](https://marsdawn.southern-light.dev/reading-notes/lilian-weng-llm-agents/index.md): Lilian Weng's widely cited 2023 survey describes an LLM agent as a brain plus planning, memory and tool use. What each part tends to leave behind for you to read, and the limitation she names in plans that don't adjust to surprises.
- [Reading notes: LangChain (Jess Ou)](https://marsdawn.southern-light.dev/reading-notes/langchain-what-is-an-agent/index.md): LangChain's 2026 “What is an AI agent?” by Jess Ou echoes Harrison Chase's 2024 definition and describes a pipeline for evaluating agents automatically. Where that pipeline still hands a step to a person, and where it doesn't.
- [Reading notes: Andrew Ng](https://marsdawn.southern-light.dev/reading-notes/andrew-ng-design-patterns/index.md): Across five letters in The Batch, Andrew Ng ranks reflection, tool use, planning and multi-agent collaboration by how reliable and predictable he finds each one — and what that ranking suggests about how closely to check each one's output.
- [Templates](https://marsdawn.southern-light.dev/templates/index.md): Markdown templates for the documents an agent writes and you read: a spec, a flowchart and meeting notes, each with a prompt for your agent.
- [Spec template](https://marsdawn.southern-light.dev/templates/spec/index.md): A Markdown spec template with requirements, a Mermaid flow diagram and acceptance criteria. Your agent fills it in; you review it in MarsDawn.
- [Flowchart template](https://marsdawn.southern-light.dev/templates/flowchart/index.md): A Mermaid flowchart template in Markdown, with the steps written out below it. Preview it on a Mac and export it to PDF.
- [Meeting notes template](https://marsdawn.southern-light.dev/templates/meeting-notes/index.md): A Markdown meeting notes template with decisions and action items, each with an owner. Your agent writes it up; you check it in MarsDawn.
- [繁體中文](https://marsdawn.southern-light.dev/zh-hant/reading-notes/harrison-chase-what-is-an-agent/index.md): Harrison Chase 2024 年對 agent 的定義，以及他自己的 agentic 光譜；他主張系統愉往自主那端走，就愉需要可觀測性——從讀那份檔案的人的角度重新看一遍。
- [简体中文](https://marsdawn.southern-light.dev/zh-hans/reading-notes/harrison-chase-what-is-an-agent/index.md): Harrison Chase 2024 年对代理的定义，以及他自己的 agentic 光谱；他主张系统愈往自主那端走，就愈需要可观测性——从读那份文件的人的角度重新看一遍。
- [日本語](https://marsdawn.southern-light.dev/ja/reading-notes/harrison-chase-what-is-an-agent/index.md): Harrison Chase による 2024 年のエージェントの定義と、彼自身の agentic なふるまいのスペクトラム。システムがそのスペクトラムを進むほど観測可能性が重要になるという彼の主張を、そのファイルを読む人の側から見直す。
- [Deutsch](https://marsdawn.southern-light.dev/de/reading-notes/harrison-chase-what-is-an-agent/index.md): Harrison Chases Definition eines Agenten von 2024 und sein Spektrum agentischen Verhaltens, und sein Plädoyer für Beobachtbarkeit, je weiter ein System darauf wandert — gelesen von der Seite der Person, die die Datei liest, die er zurückgibt.
- [Français](https://marsdawn.southern-light.dev/fr/reading-notes/harrison-chase-what-is-an-agent/index.md): La définition d’un agent de Harrison Chase en 2024 et son spectre de comportement agentic, et son plaidoyer pour l’observabilité à mesure qu’un système avance dessus — lu du côté de qui lit le fichier qu’il rend.
- [Español](https://marsdawn.southern-light.dev/es/reading-notes/harrison-chase-what-is-an-agent/index.md): La definición de agente de Harrison Chase de 2024 y su espectro de comportamiento agentic, y su argumento a favor de la observabilidad a medida que un sistema avanza por él — leído desde quien lee el archivo que te devuelve.
- [한국어](https://marsdawn.southern-light.dev/ko/reading-notes/harrison-chase-what-is-an-agent/index.md): Harrison Chase의 2024년 에이전트 정의와 agentic 행동의 스펙트럼, 그리고 시스템이 그 위를 따라갈수록 관측 가능성이 필요하다는 주장 — 에이전트가 돌려준 파일을 읽는 쪽에서의 읽기.