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Show HN: Sim Studio – Open-Source Agent Workflow GUI

186 waleedlatif1 54 4/28/2025, 4:14:31 PM github.com ↗

Hi HN! We're Emir and Waleed, and we're building Sim Studio (https://simstudio.ai), an open-source drag and drop UI for building and managing multi-agent workflows as a directed graph. You can define how agents interact with each other, use tools, and handle complex logic like branching, loops, transformations, and conditional execution.

Our repo is https://github.com/simstudioai/sim, docs are at https://docs.simstudio.ai/introduction, and we have a demo here: https://youtu.be/JlCktXTY8sE?si=uBAf0x-EKxZmT9w4

Building reliable, multi-step agent systems with current frameworks often gets complicated fast. In OpenAI's 'practical guide to building agents', they claim that the non-declarative approach and single multi-step agents are the best path forward, but from experience and experimentation, we disagree. Debugging these implicit flows across multiple agent calls and tool uses is painful, and iterating on the logic or prompts becomes slow.

We built Sim Studio because we believe defining the workflow explicitly and visually is the key to building more reliable and maintainable agentic applications. In Sim Studio, you design the entire architecture, comprising of agent blocks that have system prompts, a variety of models (hosted and local via ollama), tools with granular tool use control, and structured output.

We have plenty of pre-built integrations that you can use as standalone blocks or as tools for your agents. The nodes are all connected with if/else conditional blocks, llm-based routing, loops, and branching logic for specialized agents.

Also, the visual graph isn't just for prototyping and is actually executable. You can run simulations of the workflows 1, 10, 100 times to see how modifying any small system prompt change, underlying model, or tool call change change impacts the overall performance of the workflow.

You can trigger the workflows manually, deploy as an API and interact via HTTP, or schedule the workflows to run periodically. They can also be set up to trigger on incoming webhooks and deployed as standalone chat instances that can be password or domain-protected.

We have granular trace spans, logs, and observability built-in so you can easily compare and contrast performance across different model providers and tools. All of these things enable a tighter feedback loop and significantly faster iteration.

So far, users have built deep research agents to detect application fraud, chatbots to interface with their internal HR documentation, and agents to automate communication between manufacturing facilities.

Sim Studio is Apache 2.0 licensed, and fully open source.

We're excited about bringing a visual, workflow-centric approach to agent development. We think it makes building robust, complex agentic workflows far more accessible and reliable. We'd love to hear the HN community's thoughts!

Comments (54)

monatron · 1d ago

Hi y'all. Love the idea and congratulations on your launch. I've used [n8n](https://github.com/n8n-io/n8n) for similar use cases in the past. Any differences in Sim Studio that you'd like to call out?

ekarabeg · 1d ago

Thank you! n8n has done really well over the last few years to simplify the workflow building process. I responded to this in a previous comment, but we believe the agent building process should be more open, meaning fewer abstractions between the interface and the model provider. We want our platform to be as lightweight as possible.

How this translates in the application is through features like allowing for custom tool calling with code execution, JSON schema input for response format, etc. I'd love to hear your thoughts using Sim Studio - let us know how we compare to the other workflow builders!

skeeter2020 · 1d ago

> Building reliable, multi-step agent systems with current frameworks often gets complicated fast.

In my experience so far it's not just complicated, but effectively impossible. I struggle to get a single agent to reliably & consistently use tools, and adding n+1 agents is a error multiplier.

waleedlatif1 · 1d ago

on our platform (for the providers that allow granular tool use control), you can actually 'force' certain tool calls and have the agent dynamically select others. this was a painpoint that we faced ourselves and were confused why any frameworks didn't allow granular tool use control if the provider allows it. try it out and let us know what you think

simple10 · 1d ago

Congrats on the launch! Looking forward to playing with it.

Do you mind elaborating on what differentiates Sim Studio from n8n, Flowise, RAGFlow and other open source flow based AI automation platforms?

ekarabeg · 1d ago

Thanks! The main difference between Sim Studio and other open-source AI agent workflow builders is the level of abstraction used when creating agents.

For instance, n8n has a "memory" parameter, which is not an inherent parameter of LLMs. You can inject your agent's memories into the agent message history (or system prompt) - which is the most common scenario - but we give you control over that. We want to provide visibility, so everything that's exposed on the workflow canvas is exactly what's being executed in the background. Also, we think it's faster and more intuitive to get your workflow up and running in Sim Studio. I'd love your feedback, though! What do you think?

all2 · 1d ago

This sounds like execution/variable resolution scopes in programming languages. I wonder if there are ideas from programming languages you could pick up and use?

ekarabeg · 1d ago

Yes exactly! A lot of our platform was inspired by programming languages - for loops, for each loops, custom variables, and environment variables in settings. If you have any more concepts, we'd love to hear them!

ddon · 1d ago

Would be amazing to be able to design the workflow using your builder, and then export to code (and choose the language) and then copy paste the code into the project... just an idea.

waleedlatif1 · 1d ago

this is something we've been looking into. curious, would you rather export the code into an existing agentic framework like crewai/langgraph, or have it exported as raw code? also, would you prefer if the code was exported block-by-block or the entire workflow altogether?

handfuloflight · 1d ago

Raw code, block by block.

ekarabeg · 1d ago

Exactly

rahimnathwani · 1d ago

The UI looks lovely.

If I run Sim Studio with docker compose, how do I point it to the existing `ollama serve` instance running on the host?

I looked in settings (in the workspace UI) but don't see anywhere to configure the ollama endpoint.

waleedlatif1 · 1d ago

thank you!

for ollama running on your host machine, you'll need to modify the docker configuration since by default it's looking at http://localhost:11434 which points to localhost inside the container, not your host. you can either add `extra_hosts` as `host.docker.internal:host-gateway` to your docker compose and set the OLLAMA_HOST envvar to `OLLAMA_HOST=http://host.docker.internal:11434`, or just run `docker compose up --profile local-cpu -d --build --network=host` when running the compose command.

will add this to the readme and add in some UI locally so its easily configurable! let me know if you have any issues

rahimnathwani · 1d ago

I modified the docker-compose.yml thus:

  ...
  services:
    simstudio:
      build:
        context: .
        dockerfile: Dockerfile
      ports:
        - "3000:3000"
      volumes:
        - ./sim:/app
        - /app/node_modules
        - /app/.next
      extra_hosts:
        - "host.docker.internal:host-gateway"
      environment:
        - OLLAMA_HOST=http://host.docker.internal:11434
        - NODE_ENV=development
        - DATABASE_URL=postgresql://postgres:postgres@db:5432/simstudio
      ...

Then I ran `docker compose up -d --build`

Then I went to localhost:3000/w/

Then I added an Agent block. I expected ollama (or my ollama models) to show up in the drop-down, but I only see the hosted models.

I even tried editing `sim/providers/ollama/index.ts`:

  const OLLAMA_HOST = 'http://host.docker.internal:11434'

Any ideas?

(BTW I did NOT run `--profile local-cpu` because I didn't want to run ollama in a docker container, as it's already running on the host.)

waleedlatif1 · 1d ago

i think it could be one of a few things: - first, even though your ollama is running on the host, you still need to use the local profile flag to enable ollama models in the UI. you can do this by running the docker compose command with `local-cpu` - also, make sure your host ollama is actually running and responding (curl http://localhost:11434/api/tags should show your models) - if neither of the above work, you may need to restart the app container after changing the OLLAMA_HOST value

rahimnathwani · 1d ago

I see this in the docker compose logs, but those models don't show up in the model drop-down on the Agent block:

  simstudio-1  | [2025-04-29T03:41:12.195Z] [INFO] [OllamaStore] Updating Ollama models {
  simstudio-1  |   "models": [
  simstudio-1  |     "hf.co/bartowski/Qwen_Qwen3-32B-GGUF:latest",
  simstudio-1  |     "qwen3:30b-a3b-q4_K_M",
  simstudio-1  |     "gemma3:12b-it-qat",
  simstudio-1  |     "gemma3:4b-it-q4_K_M",
  simstudio-1  |     "nomic-embed-text:latest"
  simstudio-1  |   ]
  simstudio-1  | }
  simstudio-1  | [2025-04-29T03:41:12.195Z] [INFO] [ProviderUtils] Updated Ollama provider models {
  simstudio-1  |   "models": [
  simstudio-1  |     "hf.co/bartowski/Qwen_Qwen3-32B-GGUF:latest",
  simstudio-1  |     "qwen3:30b-a3b-q4_K_M",
  simstudio-1  |     "gemma3:12b-it-qat",
  simstudio-1  |     "gemma3:4b-it-q4_K_M",
  simstudio-1  |     "nomic-embed-text:latest"
  simstudio-1  |   ]
  simstudio-1  | }

Whether or not I include `--profile local-cpu` in the docker compose command:

- the models from my local ollama show up in the logs, and

- the models don't show up in the model drop-down in the Agent block.

AFAICT the only impact of `--profile local-cpu` is starting a docker container with ollama running.

waleedlatif1 · 1d ago

just pushed a hotfix that should resolve this for you! let me know if you are still having issues. we recently updated the csp and needed to explicitly add the ollama endpoint to the connect-src directive

rahimnathwani · 1d ago

I updated, deleted docker volumes, and retried, and I still see the same issue :(

badmonster · 16h ago

How can I add a custom tool or integration to Sim Studio and have it appear in the workflow builder UI?

waleedlatif1 · 9h ago

If you want to add a custom tool for your agent to use, you can use the “add custom tool” in the agent block and just define the JSON schema and the code for the tool call.

If you want a custom integration, you can either request it, or if you are running locally we have really thorough instructions on how you can add a tool/block in the contributing guide for the repo. You can use this to extend the platform for yourself or add integrations to the main repo. Hope that helps!

artem_zin · 1d ago

Youtube demo looks intriguing, I'm self-hosting n8n for exact this purpose with a home run LLM machine in a local k8s cluster (lol) but out of the box I can tell your tool surpasses AI integrations and workflow in n8n.

Quick glance at GitHub suggests that GitHub package for the Docker image is missing, let me know if you need help with that — happy to contribute!

vseplet · 1d ago

It's funny, but I solved a similar problem myself, but instead of n8n I came to write my own solution. I even noticed this post thanks to automation and llm. Likewise, I'll be glad to help!

waleedlatif1 · 1d ago

thanks! that would be awesome to have, always welcome contributors :)

joshcsimmons · 1d ago

Congrats on the launch the tool looks phenomenal.

I’m conflicted because n8n does feel like the right level of abstraction but the UI and dated JS runtime environment are horrible. I don’t really want to write my own memory functionality for my AI agents but wondering if it’s worth it just to have a nicer UI and more modern JS env.

waleedlatif1 · 1d ago

for ease of use, we are exploring a way to add in short-term and medium-term memory out of the box in a way that doesn't require us to inject anything into the agent's context unless the user explicitly wants to. for longer-term memory, we support popular vector DB's like pinecone and integrations with mem0

gavmor · 1d ago

I'm sure that the complex logic and state management were not trivial to implement, but the link said GUI so I wanted to see some screenshots, but all I saw were two very dim simple forms.

This space is REALLY struggling to graduate from Gradio-like design sensibilities.

That being said, I'm looking forward to playing with this, congrats on the launch!

nico · 1d ago

The video linked in the post description shows everything pretty clearly, here: https://www.youtube.com/watch?v=JlCktXTY8sE

rancar2 · 1d ago

The screenshot on the website are helpful, and it would be good to add them into the GitHub documentation as the OP mentioned.

waleedlatif1 · 1d ago

thanks for the feedback! adding some screenshots to the docs showcasing more complex workflows we've created so far

dr_kiszonka · 1d ago

It looks very nice. What happens when a flow that takes 1 minute to complete is triggered by three different Slack messages from different users one second apart. Are flow executions queued or executed in parallel? Is it configurable?

waleedlatif1 · 1d ago

thanks! this would actually trigger three separate workflow executions, and the messages would be processed in parallel by each execution. by default, within the workflow all the blocks execute once their dependencies are resolved, and for the workflow itself they are also executed in parallel. if three messages are sent by the same user, it is also executed as separate workflow executions. curious to hear about your usecase though, are you looking to process the messages in batches?

dr_kiszonka · 1d ago

Thanks for replying so quickly and in detail. I wanted to understand issues around scalability and integration into a larger system.

I have been looking for a good solution in this increasingly crowded space and if I could offer a word of unsolicited advice it would be to ensure documentation is top notch, truthful (some competitors mention non-existent features in their docs), and includes a relatively detailed roadmap.

Good luck with Sim Studio. I may try it out in a few weeks!

waleedlatif1 · 1d ago

of course! we will be sure to keep the most up-to-date & accurate documentation and document all of the intricacies like this one, and create a roadmap as well. excited for you to try it out and let us know what you think

brene · 1d ago

I checked it out and it’s quite polished for a workflow builder. But I struggled for it to handle lists of content well. But I saw that’s already an ongoing feature request.

ekarabeg · 1d ago

Thank you! Yes - we are adding variable resolution to the for each input. Let us know if there's anything else you'd like to see!

dmos62 · 1d ago

What are your main competitors for agent orchestration with observability?

ekarabeg · 1d ago

The big names out there are n8n and flowwise. I'd encourage you to try them out and let us know what you think compared to Sim Studio! We have a logs page that shows execution duration, tool call duration, tokens used, the cost based on the model you selected, etc.

dmos62 · 1d ago

Thanks. It would be nice to find your expert comparison of Sim Studio to these other tools in your docs. The comparisons you already made in this thread is a great resource too ofc.

gitroom · 1d ago

This is pretty sick, I love having that much control without having to hack around a bunch of stuff.

waleedlatif1 · 1d ago

thank you and exactly! that's why we built it. trigger it many different ways, swap out tools, models, etc. Just focus on the things that matter for agent performance and ignore everything else

neil_s · 1d ago

Much simpler UI than n8n, congrats on the launch!

waleedlatif1 · 1d ago

thanks!

djjose · 1d ago

Nearly 20 years later, it's fascinating to see Yahoo! Pipes for AI Agents.

pjpr · 1d ago

congrats on the launch!!

waleedlatif1 · 1d ago

thanks!

deshraj · 1d ago

Congratulations, Emir and Waleed! This is exactly the kind of OSS tooling I’ve been waiting for. I’ve spent countless hours wrestling with multi-step agent workflows hidden inside monolithic prompts, and every iteration felt like shooting in the dark. Having a drag-and-drop, executable graph with built-in branching, loops, and observability is a game-changer.

waleedlatif1 · 1d ago

thank you! check out the mem0 integration and let us know if you like the form factor. excited for you to check out the platform and let us know if it helps you wrangle those multi-step agent workflows.

frabonacci · 1d ago

This could play very well with building a managed agentic system around computer-use for RPA. Great stuff!

waleedlatif1 · 1d ago

we have support for browser agents (browser-use and stagehand), but running this locally with computer use agents would change the game. will explore :)

nico · 1d ago

Can the browser agents use my already running browser? It would be nice to automate some light workflows in platforms that require login, especially the ones that make it hard to use headless browsers

Right now my solution is to build extensions that I can manually start on my browser. But using extensions to gather and export data + maintaining them is a bit of a pain

waleedlatif1 · 1d ago

yeah! for stagehand, I actually stitched together a way for you to login and authenticate on platforms without the LLM's ever seeing your login credentials. in the prompt, you can specify the username as %username% and provide the credentials right below, and then we use selectors to enter that value into the DOM and hand it back to the agent once the login is completed. you can also get structured output. afaik, stagehand themselves don't even offer these three in their SDK and there's no way to login without giving the LLM your credentials. it isn't the best, but its the only place I've seen you can get secure login + agents + structured output

nico · 1d ago

Amazing. Can it also use multimodal local LLMs? For example, can it pass images to gemma3 running via ollama?

waleedlatif1 · 1d ago

although I haven't experimented with gemma 3 locally, with ollama we have instructions in the README, and all you need to do is initialize the model, and pull it when running sim studio. let me know how it goes!

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Show HN: Sim Studio – Open-Source Agent Workflow GUI

Comments (54)