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Launch HN: Human Layer (YC F24) – Human-in-the-Loop API for AI Systems

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Launch HN: Human Layer (YC F24) – Human-in-the-Loop API for AI Systems

#1
Hey HN! I'm Dex, building HumanLayer (https://humanlayer.dev), an API that lets AI agents contact humans for feedback, input, and approvals. We enable safe deployment of autonomous/headless AI systems in production. You can try it with our Python or TypeScript SDKs and start using it immediately with a free trial. We have a free tier and transparent usage-based pricing. Here’s a demo: https://youtu.be/5sbN8rh_S5Q?t=51

What's really exciting is that we're enabling teams to deploy AI systems that would otherwise be too risky. We let you focus on building powerful agents while knowing that critical steps will always get a human-in-the-loop. It's been dope seeing people start to think bigger when they consider dynamic human oversight as a key ingredient in production AI systems.

This started when we were building AI agents for data teams. We wanted to automate tedious tasks like dropping unused tables, but customers were (rightfully!) opposed to giving AI agents direct access to production systems.

Getting AI to "production grade" reliability is a function of "how risky is this task the AI is performing". We didn't have the 3+ months it would have taken to sink into evals, fine tuning, and prompt engineering to get to a point where the agent had 99.9+% reliability—and even then, getting decision makers comfortable with flipping the switch on was a challenge. So instead we built some basic approval flows, like "ask in Slack before dropping tables".

But this communication itself needed guardrails—what if the agent contacted the wrong person? How would the head of data look if a tool he bought sent a nagging Slack message to the CEO? Our buyers wanted the agent to ask stakeholders for approval, but first they wanted to approve the "ask for approval" action itself. And then I started thinking about it... as a product builder + owner, I wanted to approve the "ask for approval to ask for approval" action!

I hacked together a human-AI interaction that would handle each of these cases across both my and my customers' Slack instances. By this time, I was convinced that any team building AI agents would need this kind of infrastructure and decided to build it as a standalone product. I presented the MVP at an AI meetup in SF and had a ton of incredible conversations, and went all in on building HumanLayer.

When you integrate the HumanLayer SDK, your AI agent can request human approval at any point in its execution. We handle all the complexity of routing these requests to the right people through their preferred channels (Slack or email, SMS and Teams coming soon), managing state while waiting for responses, and providing a complete audit trail. In addition to "ask for approval", we also support a more generic "human as tool" function that can be exposed to an LLM or agent framework, and will handle collecting a human response to a generic question like "I'm stuck on $PROBLEM, I've tried $THINGS, please advise" (I get messages like this sometimes from in-house agents we rolled out for back-office automations).

Because it's at the tool-calling layer, HumanLayer's SDK works with any AI framework like CrewAI, LangChain, etc, and any language model that supports tool calling. If you're rolling your own agentic/tools loop, you can use lower level SDK primitives to manage approvals however you want. We're even exploring use cases where HumanLayer is used for human-to-human approval, not just AI-to-human.

We're already seeing HumanLayer used in some cool ways. One customer built an AI SDR that drafts personalized sales emails but asks for human approval in Slack before sending anything to prospects. Another uses it to power an AI newsletter where subscribers can have email conversations with the content. HumanLayer handles receiving inbound emails and routing them to agents that can respond, and giving those agents tools to do so. One team uses HumanLayer to build a customer-facing DevOps agent—their AI agent reviews PRs, plans and executes db migrations, all while getting human sign-off at critical steps and reaching out to the team for steering if it encounters any issues.

We have a free tier and flexible credits-based pricing. For teams building customer-facing agents, you get whitelabeling and additional features and priority support.

If you want to integrate HumanLayer into your systems, check out our docs at https://humanlayer.dev/docs or book a demo at https://humanlayer.dev.

Thank you for reading! We’re admittedly early and I welcome your ideas and experiences as it relates to agents, reliability, and balancing human+AI workloads.

Re: Launch HN: Human Layer (YC F24) – Human-in-the-Loop API for AI Systems

#2
P.S. nobody asked but since you made it this far - the next big problem in this space is fast becoming, what else do we need to be able to build these "headless" or "outer loop" AI agents? Most frameworks do a bad job of handling any tool call that would be asynchronous or long running (imagine an agent calling a tool and having to hang for hours or days while waiting for a response from a human). Rewiring existing frameworks to support this is either hard or impossible, because you have to

1. fire the async request, 2. store the current context window somewhere, 3. catch a webhook, 4. map it back to the original agent/context, 5. append the webhook response to the context window, 6. resume execution with the updated context window.

I have some ideas but I'll save that one for another post :) Thanks again for reading!

Re: Launch HN: Human Layer (YC F24) – Human-in-the-Loop API for AI Systems

#5
post #2

P.S. nobody asked but since you made it this far - the next big problem in this space is fast becoming, what else do we need to be able to build these "headless" or "outer loop" AI agents? Most frameworks do a bad job of handling any tool call that would be asynchronous or long running (imagine an agent calling a tool and having to hang for hours or days while waiting for a response from a human). Rewiring existing f…

Temporal makes this easy and works great for such use cases. It's what I'm using for my own AI agents.

Re: Launch HN: Human Layer (YC F24) – Human-in-the-Loop API for AI Systems

#6
post #5
post #2

P.S. nobody asked but since you made it this far - the next big problem in this space is fast becoming, what else do we need to be able to build these "headless" or "outer loop" AI agents? Most frameworks do a bad job of handling any tool call that would be asynchronous or long running (imagine an agent calling a tool and having to hang for hours or days while waiting for a response from a human). Rewiring existing f…

Temporal makes this easy and works great for such use cases. It's what I'm using for my own AI agents.

ah very cool! are there any things you wish it did or any friction points? What are the things that "just work"?

Re: Launch HN: Human Layer (YC F24) – Human-in-the-Loop API for AI Systems

#7
post #3

Loving you guys have Typescript support from day one!

hah thanks dude! I am very bullish on TS as the long term thing, Not to turn this into a language vs language thread but I spend a lot of time thinking about why ppl struggle so much with python...so far I came up with

concurrency abstractions keep changing (still transitioning / straddling sync+threads vs. asyncio) - this makes performance eng really hard

package management somehow less mature than JS - pip been around way longer than npm but JS got yarn/lockfiles before python got poetry

the types are fake (also true of typescript, I think this one is a wash)

the types are fake and newer. typing+pydantic is kinda bulky vs. TS having really strong native language support (even if only at compile time)

virtual environments!?! cmon how have we not solved this yet

wtf is a miniconda

VSCode has incredible TS support out of the box, python is via a community plugin, and not as many language server features

Re: Launch HN: Human Layer (YC F24) – Human-in-the-Loop API for AI Systems

#10
My favorite part of all this is that it’s inevitable. Someone has to solve agent adoption in whatever-the-environment-already-is. And nobody is doing this well at scale. Europe is mandating this. And even though Article 14 of the AI Act won’t be enforced until 2026, I’m glad projects like this are working ahead. Get after it, Dex!
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