Deep Dive · Agent harnesses

How to Talk to an Agent That Builds Its Own App

DeepSeek published the seven prompts behind its Creator Mode demos, and they read less like magic spells than a specification of what a prompt for a plugin-building agent needs: where it lives, what it does, the numbers, the defaults, what to leave out, and how it talks back to the conversation. Plus the honest caveat DeepSeek added itself — and the token bill nobody mentions.

Deepseek is Actually Redefining Harnesses! — video thumbnail
Video: AICodeKing 9:11 4 November 2026
DeepSeek Harness Creator Mode Prompt design Plugins

📄 What DeepSeek published 0:03

DeepSeek had already shown what Creator Mode can do in a short demo — an app that writes its own plugins while you talk to it — with a 3D landmark gallery, a Transformer visualiser, a pixel-art skin for the whole app, and more. Everybody wanted the prompts. DeepSeek then published all of them: one page, seven prompts, in English and Chinese, with a copy button on each.

"This page is more useful than it looks, because if you read these prompts closely, they are basically a guide to how you should talk to Creator Mode."
Fact about the releaseDetail
Demos shownSeven plugins, including a 3D landmark gallery, a Transformer visualiser, a pixel-art interface skin, a poster workbench, a video editor, a paper reader and a conversation-statistics dashboard
Prompts publishedAll seven, in English and Chinese, each with a copy button
How to use themCopy a prompt, paste into DeepSeek Harness, select Creator Mode
Harness itselfOpen source, MIT, "everything is a plugin"; ~272,000 GitHub stars as of this writing
Disclosure. This video has a sponsor, and roughly a third of it is a walkthrough of that vendor's subscription and desktop app. All of that promotional material — pricing, discount links, product URLs — is excluded here. The one technically useful idea from that segment is noted separately in The token bill: DeepSeek Harness accepts a custom model provider over an OpenAI-compatible protocol, which is a general capability, not a vendor feature.

🧩 Creator Mode in ninety seconds 0:48

DeepSeek Harness ships several modes. Standard is the normal coding agent. Creator is the one that builds plugins, and the mechanism matters for understanding the prompts:

StepWhat Creator Mode does
1. InspectAdds two read-only tools so the agent can look inside the running app before writing anything — list what is loaded, and check the exact methods and types available
2. WriteAuthors the plugin against that real surface, not against an imagined API
3. Package and installPackages it as a bundle and installs it through the plugin manager
4. PersistThe plugin belongs to your profile, so it survives a restart
The two read-only tools are the real engineering. A plugin-writing agent's classic failure is inventing an API that does not exist — then producing code that looks plausible and crashes. Letting the agent introspect the live runtime before it writes turns "hallucinate an interface" into "read the interface". Every prompt on DeepSeek's page assumes this step is available, which is why the prompts can be short.

The current build at the time of the video was a release candidate from 30 October (v0.2.1-rc.5); releases have continued since, with v0.2.2-rc.1 landing on 4 November. That cadence is itself a caveat, and the video treats it as one.

⚠️ The caveat they volunteered 1:31

On the page, next to the prompts, DeepSeek says plainly that some of these plugins were refined over several rounds of conversation — so a single prompt may not reproduce exactly what you saw in the demo video.

"These are starting points, not magic spells."

That one sentence is the most honest thing in the release, and it is also the thing that makes the rest of the video expensive: every artefact you saw in a demo is the endpoint of a conversation, not the output of a copy-paste.

🔍 The seven prompts, and what each teaches 1:45

#PluginWhat the prompt specifiesLesson
13D landmark galleryA left-sidebar entry that renders 3D models of the Eiffel Tower, the Great Wall, the Forbidden City, and "one more famous building of the model's choice"Say where it lives — and leave a little room for taste
2Transformer 3D visualiserAn interactive 3D demonstration of the computation inside a Transformer — plus: keep the panel title and toolbar clear of the native macOS window buttonsWhen something looks broken, name the exact problem instead of starting over
3Pixel-art interface skinA plugin that restyles the whole app, with five styles to choose from, pixelated among themGive it a count: five styles, not "some styles"
4Poster design workbenchOpens from the conversation; use the shader background pattern and English font from the DeepSeek Harness website; customisable title, text and shader colours; default page minimal with no unnecessary subheadings; default title "everything is a plugin"Say what you don't want, and give the defaults
5Video editing workbenchDark interface, familiar editor interactions, multiple uploads, editing and export, large preview on top with a timeline below — and the ability to import and edit via natural language in the chatDescribe layout like a wireframe, and connect the plugin back to the conversation
6Paper readerRight sidebar; upload papers; preserve original layout, fonts and images without loss; selecting text opens a floating menu with three options — highlight, add note, ask in conversation; the default question must match the interface languageSpell out the interaction step by step
7Conversation statisticsBuilt on your actual conversation data: total token usage, conversation count, estimated cost, a budget based on that usage, a token timeline, usage and cost per conversation, CPU activity and utilisationSay "real data", or you get a beautiful dashboard full of fake numbers

One structural detail is easy to miss: six of the seven prompts say where the plugin lives — three in the left sidebar, two opened from the conversation, one in the right sidebar. The seventh, conversation statistics, does not, and the model has to guess. That is the natural first lesson, because placement is the one thing a plugin-building agent cannot infer from what the plugin does.

The most instructive prompt is the second one, and it is instructive for what it reveals about iteration. "Keep the panel title and toolbar clear of the native macOS window buttons" is not a design instruction — it is a bug report, written after an earlier attempt overlapped the traffic lights. Its presence on the published page is evidence that the multi-round caveat is real, and a useful habit: every prompt you publish should contain the scars of the previous version.

🧭 The five parts of a good prompt 5:19

PartExample from the sevenWhat it prevents
Where it lives"A left sidebar entry"The agent picking a random surface and calling it done
What it does"Renders 3D models of…" / "estimates cost from usage"A vague tool that looks right and does nothing
The numbers and defaults"Five styles", default title "everything is a plugin", budget derived from real usagePlaceholder values and "some" instead of a countable thing
What to leave out"Minimal, with no unnecessary subheadings"Filler — models add structure when they are unsure
How it connects back"Import and edit videos with natural-language requests in the conversation"A static panel instead of something the agent can drive

This is a good checklist for any tool-building prompt, not just DeepSeek's: the five parts correspond to the five questions that decide whether an artefact is usable — where do I find it, what does it do, what are its exact values, what is it not, and how do I operate it.

🔬 Why this grammar works 5:30

Three of the five parts are counter-intuitive, and each maps onto a specific failure mode of generation:

  • Counts beat adjectives. "Five styles" is checkable; "some styles" is a vibe. A requirement you can count is a requirement the agent can finish.
  • Defaults are requirements. Specifying the default title or the default page state is how you stop the model from optimising the first impression and leaving the steady state empty.
  • Negative space is design. "No unnecessary subheadings" works because models are trained on a world where thorough-looking output is rewarded. Telling it what to omit is the only way to spend its thoroughness where you want it.
And one lesson the video states better than most prompt guides: say "real data" explicitly. A dashboard built from invented numbers looks more convincing than one built from real ones, because fake data has no gaps. The seventh prompt's insistence on actual conversation data is a spec, not a nicety.

💸 The token bill 5:31

Here the video turns commercial, and the underlying problem is real: Creator Mode reads the runtime, writes the plugin, installs it, and then you iterate on details — which is a lot of tokens per plugin, and it multiplies with every round of conversation.

ApproachTrade-off
Pay per token on a frontier modelHonest cost, highest quality; the multi-round caveat makes this the expensive path
Use a subscription that fronts several open modelsSmooths the iteration cost; quality varies per model
Route big plugins to a strong model, small fixes to a fast oneThe right default regardless of who you buy from

The technically useful part of that segment is a capability of the harness, not a product: DeepSeek Harness accepts a custom model provider over the OpenAI Chat Completions protocol (Settings → Models → add a provider → custom base URL → paste key → fetch available models). Any OpenAI-compatible endpoint therefore works, including a local server.

Tiered model choice is the durable lesson: run Creator Mode's heavy plugin generation on the strongest model you can afford, and hand the "move that toolbar 8 pixels" rounds to something fast and cheap. The cost of a plugin is dominated by iterations, not by the first generation — so that is where the routing belongs.

🔀 Running it in parallel 7:19

The last idea is the most interesting architecturally: a separate workspace tool can launch DeepSeek Harness as one of its harnesses — installing the DSH package from npm, launching it over ACP, listing its models and setting reasoning effort.

LayerRole
OrchestratorHolds the whole task and the context
Worker ADeepSeek Harness, on its own model, doing Creator Mode work
Worker BA second harness on a different model, doing something else

Practically: all seven plugin ideas could be handed out in parallel to different workers and reviewed in one place. That is only possible because DSH exposes itself over a protocol rather than only as a GUI — the same property that made MCP and AG-UI useful elsewhere.

A licensing detail the video does not mention: the workspace tool it promotes (PandaCode, the channel's own project) is listed on GitHub without an SPDX-recognised licence (NOASSERTION). That means source-available, not open source in the OSI sense — worth knowing before you build a workflow on it.

🚧 What can go wrong 7:46

LimitationWhat it means in practice
Developer previewRelease candidates ship often; behaviour can change between builds
Single prompts are starting pointsDeepSeek says it themselves — expect to iterate, budget for the rounds
Whole-app plugins can break the lookA pixel skin that restyles everything can also make the app unusable; there is nowhere to turn it off except the plugin manager
Subscriptions are finiteRunning Creator Mode all day on the best model hits limits
Beta toolingThe desktop app and orchestration layer are early; expect rough edges
The whole-app plugin problem is worth taking seriously as a design constraint, not a joke. A plugin that can restyle the entire interface can also remove your ability to find the plugin manager. If a harness lets plugins touch the chrome, it needs a recovery path that does not depend on the chrome — a keyboard chord, a CLI flag, a safe mode.

🧠 What it says about harnesses 8:30

Strip away the sponsor and the demo list, and DeepSeek has shipped three things that together are a small thesis about where harnesses are going:

  1. The interface is part of the harness. Because everything is a plugin — including the chrome — the agent is not limited to adding tools; it can add surfaces. The pixel skin prompt is the proof: "this is the app changing itself".
  2. The agent needs read access to its own runtime. The two read-only introspection tools are what make plugin generation reliable rather than hopeful, and they are the pattern worth copying in any agent that writes code against its own platform.
  3. Prompts become specifications you can publish. Seven copyable prompts that reproduce seven artefacts is a new kind of documentation — closer to a recipe book than an API reference, and honest about needing a cook.
"Say where it lives, give it numbers and defaults, say what to leave out, and connect it back to the chat."

Whether this "redefines harnesses" is a claim that only usage will settle. What is already true: a harness whose extension mechanism is a conversation has to get two things right — introspection, so the agent writes against reality, and recovery, so a bad extension can be undone. DeepSeek built the first; the second is currently one plugin manager page deep.

✅ Claims checked

ClaimVerdictEvidence
DeepSeek published seven Creator Mode prompts, in English and Chinese, with copy buttonsCorrectCorroborated by TechNode, Mashable, Dataconomy (Nov 3) and DeepSeek's own site describing Creator Mode; the prompts page itself was not reachable from the sitemap, so the per-prompt detail below is the video's reading of it
Creator Mode adds two read-only tools to inspect the running appConsistentMatches DeepSeek's description of plugins extending "tools, skills, and the interface"; specific tool count is the video's
Plugins are packaged as a bundle, installed via the plugin manager, and persist per profileConsistentMatches the plugin-manager model shown on DeepSeek's harness page
Harness is MIT, open source, "everything is a plugin"Correctdeepseek-ai/deepseek-harness: MIT, ~272,400 stars at time of writing
Current build: release candidate from 30 October (v0.2.1-rc.5)CorrectGitHub releases: dsh-v0.2.1-rc.5 published 2026-10-30; dsh-v0.2.2-rc.1 followed on 2026-11-04, after the video
Six of seven prompts specify where the plugin lives (3 left, 2 in conversation, 1 right)Video's countNot independently checkable without the prompts page; internally consistent with the descriptions
DeepSeek says some plugins took several rounds of conversationCorrect — and quoted by pressMashable quotes it verbatim: "some plugins were refined through several rounds of conversation"
Harness accepts a custom model provider over an OpenAI-compatible protocolConsistentStandard for DSH ("not locked to DeepSeek models"; OpenAI-compatible endpoints)
PandaCode can launch DSH over ACP with its own modelsPlausible; licence caveataicodeking/pandacode exists (~1,060★) but carries NOASSERTION — source-available, not OSI open source
Sponsor's price, model lineup and bundled usageCommercial claimsSponsor segment; excluded from this article and not repeated as fact
The seven demo plugins listed in the videoPartly divergent from press coverageCoverage also mentions a sticky-note wall, a sandbox game and a Pomodoro timer; the video enumerates a different set of seven. The official page could not be fetched to arbitrate

Basis note. Built from the full 9:11 transcript. The release facts (licence, stars, release-candidate dates, the "several rounds" caveat) were checked against GitHub and the outlets that covered the launch; the per-prompt contents are the video's reading, because DeepSeek's prompts page was not reachable from the documented site paths when this was written. That gap is stated rather than papered over. Sponsor material is excluded, and one correction was made: the workspace tool is PandaCode, and it is not licensed as open source.

🔑 Key takeaways

  • The prompts are the documentation. Seven copyable specs that reproduce seven artefacts is a new documentation format — a recipe book, not an API reference.
  • Say where it lives. Placement is the one thing a plugin-building agent cannot infer from what the plugin does; six of seven published prompts specify it.
  • Counts beat adjectives. "Five styles" is checkable; "some styles" is a mood. If you can count a requirement, the agent can finish it.
  • Defaults are requirements. Specifying the default title and page state is how you control the steady state, not just the first impression.
  • Say what to leave out. Models add filler when unsure; the negative instruction is the only way to spend their thoroughness where you want it.
  • Say "real data" out loud. Fake numbers produce a more convincing dashboard than real ones, because they have no gaps.
  • Connect the plugin back to the conversation. A panel the agent can drive is worth more than a panel you can click.
  • The two read-only introspection tools are the real engineering. Read the live runtime before writing code and you stop hallucinating an API that does not exist.
  • The published prompts carry their scars. A line about clearing the macOS window buttons is a bug report from the previous attempt — keep those lines in your prompts.
  • Iterations, not generation, dominate cost. Route the big build to the strongest model and the small fixes to a fast one; DeepSeek says a single prompt rarely reproduces the demo.
  • The interface is now part of the extension surface — which is powerful and dangerous: a plugin that restyles everything needs a recovery path that does not depend on the restyled chrome.
  • Check licences before building a workflow on a tool. The promoted orchestration app is source-available (NOASSERTION), not OSI open source.

🔗 Resources

Basis note. The prompts page itself could not be opened at the documented site paths (the sitemap lists only the harness landing, privacy and terms pages), so the per-prompt descriptions here are the video's reading, cross-checked for plausibility against how DeepSeek describes Creator Mode and against three independent reports of the launch. Where the video's list of seven demos diverges from press coverage, the claims table says so.

⏱ Timestamp index

0:03DeepSeek published the seven prompts
0:48Refresher: Harness, modes, versions
1:05Creator Mode's two read-only tools
1:31The multi-round caveat
1:45Prompt 1: the 3D landmark gallery
2:21Prompt 2: Transformer visualiser, and the macOS buttons
2:48Prompt 3: pixel-art skin for the whole app
3:20Prompt 4: poster design workbench
3:52Prompt 5: video editing workbench
4:21Prompt 6: paper reader
4:50Prompt 7: conversation statistics, and "real data"
5:19The five parts of a good prompt
5:31The cost of iteration
6:08Adding a custom model provider in Settings
7:19Running DSH as a worker over ACP
7:46Limitations: preview, iteration, whole-app plugins
8:30Recap of the prompt grammar
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