Show HN: Reverse-engineering web apps into agent tools

Hey HN! We built a browser-based agent that runs inside an authenticated web app, watches how the app calls its own APIs, and automatically turns those into agent tools. You can think of it as an auto-generated MCP server that self-updates as the host app changes.

The result is a skilled AI assistant that actually integrates deeply with any product (not just chat and RAG) with minimal effort.

Check out these short demos below that show the agent in software you're probably familiar with:

- Jira: https://demo.frigade.com/hn?skill=jira

- Spotify: https://demo.frigade.com/hn?skill=spotify

- Hacker News (lol): https://demo.frigade.com/hn?skill=hackernews

- Full Demo: https://demo.frigade.com/hn?skill=full-demo

As you can see in the examples, you can do way more (and faster) than what you normally would be able to via point and click. And we never even touched the source code of these products!

Why do this?

In an ideal world, every application has an MCP server or an easily-digestible API available for AI agents to feed from. In practice, we found that even very modern software tends to have a spider web of confusing APIs and services that AI agents simply cannot use out of the box. Security also becomes a huge issue as applications have different (often homebrewed) standards for how endpoints are secured (JWTs/cookies/mix of both). Finally, having an actual browser agent go in and use the application on behalf of the user (i.e. computer-use), is simply too brittle, slow, and burns a lot of tokens.

We took our existing browser agent that’s already trained to use and learn authenticated applications, and added an extra step that automatically turns the app’s authenticated APIs into "recipes". A recipe is a mix of the following:

- API endpoint + method

- Authentication method (and how to retrieve refresh auth tokens/cookies)

- Response schema

- Input schema (for POST/PUT)

- Human readable description of what the tool does

Putting it all together, these become reusable tools for LLMs, all without writing or maintaining any code. Even if the APIs change our agent figures this out and replaces the recipe for the tool with the updated version.

Adding tools to an AI agent becomes super simple this way:

- Our agent trains on the app and builds the recipes

- The app owner enables discovered tools from our dashboard

- The agent can now take actions on the user’s behalf directly inside the application. For instance, saying something like "invite my teammate to my workspace" would securely call the existing API endpoint for inviting users without proxying or relaying through a third party.

Of course, there's a ton of edge cases you run into when you try to do this - every application is intrinsically different despite how many "standards" exist. Fun fact: graphql was by far the worst API to work with in standardizing the recipes.

Looking forward to your feedback/comments!

89 points | by pancomplex 2 days ago

24 comments

  • throwawayk7h 2 hours ago
    This is going to wind up with remote attestation being implemented into web browsers to prevent this exact thing (and conveniently for google, this will finally end adblock)
  • hoppp 1 day ago
    How do you make sure you are not violating terms and conditions if they forbid injecting third party javascript into the website explicitly?

    Does your LLM ingest terms and conditions too?

    In some cases in the past, finding and using auth tokens in the front end has resulted in hacking charges, in those cases alleged hacker found an api key in the front end and directly accessed the database, which resulted in a jail sentance.

    How do you solve this issue that some companies may become hostile if injected code extracts auth tokens and accesses backend?

    • enos_feedler 19 hours ago
      Many years ago I wrote a simple script to periodically pull my aeroplan miles from Air Canada using an extracted auth token. I was building my own mobile app to track all kinds of important numbers in my life. One day I woke up to my air canada account being nuked without access. I was on the phone for 3 days talking to many layers of support. At one point they were not going to re-enable my account and would lose 400k points. I was devastated. Thankfully i was able to get it back eventually. This whole era of using LLMs to manipulate services on the client is not going to end well. We need proper business-level support or its just an irresponsible hack you are letting loose into the wild.
    • pancomplex 14 hours ago
      We only do this with consent from the application owner - the use case is typically companies who don’t have an AI agent yet who want fast path to get one.

      This is the process we usually do: https://frigade.com/how-it-works

  • hajimuz 1 day ago
    This is really helpful. I usually manually do this with chrome dev tools, it’s kind of tedious especially the header and cookies handling.
    • pancomplex 1 day ago
      Agreed - and especially when the API changes..
  • nixus76 1 day ago
    Very cool! Does it require some kind of scraping of a third party web app, like clicking through with a browser agent? If so, how can I be sure it does not delete my account or subscribe to another plan or make some other destructive actions if I allow it to do that with my authed acct?
    • pancomplex 1 day ago
      We use a browser-based agent to learn all the APIs and turn them into skills. Most users will run this in a staging/test account to create all the recipes/blueprints. Our agent is also instructed to not take any destructive actions - but of course LLMs make mistakes (hence the test account :) ).

      You can see more about how it works in detail here: https://frigade.com/how-it-works

      • nixus76 1 day ago
        Got it- so it is "inside-out", not "outside-in" kind of product. Very impressive either case, congrats!

        How does it work with the intercom widget though?

        • pancomplex 1 day ago
          We can either replace an intercom widget entirely or do a hand off with context to a live intercom chat agent.
  • arjunchint 1 day ago
    I am not following a couple of things:

    - you sell to websites an in-app agent

    - why not just have them give you API spec, why reverse engineer their APIs?

    A bit longer term, would you see yourself competing with WebMCP then? Because the website can just expose those APIs to any browser agent

    • pancomplex 1 day ago
      Even with an API spec it wouldn't "just work". You'd still need to handle authentication and have a place to manage which APIs you want the in-app agent to have access to / when to call a given tool.

      And believe it or not, even big companies with big eng teams don't have API specs available for their applications ¯\_(ツ)_/¯

      • johnpaulkiser 1 day ago
        Yeah the auth angle and unobtrusive integration path seems like the real neat thing here. From your customers eyes its just another user account right?

        Is that a requirement to integrate it? your app has to essentially have "teams" or at least shared resources?

        • pancomplex 1 day ago
          Yup just another user account. It can work without this as well (we support ingesting other resources such as help center articles, pdfs, etc.) but at that point it's no different from any other (dumb) AI chatbot out there that just spits out a bunch of itemized bullets.
  • quarkcarbon279 1 day ago
    I'm so surprised you didn't add your agent on your own website? And the same fundamentals of a browser agent why you can't achieve everything with APIs alone apply here too inside a website. What's your take?

    We have been building in the space balancing both with priority to GUI tools currently building on top of the great GUI experiences of a product, rtrvr.ai/rover

  • teravor 1 day ago
    it's more useful when you don't need permissions from anyone.

    1) get firefox MCP

    2) visit target site

    3) point GLM 5.2 to MCP (maybe grok 4.5 will also work here? haven't tested their guardrails yet)

    4) instruct model to create userscript that augments/breaks whatever you want, or just break it with devtools for the one session.

    between 3 and 4 you may want to coax the model into instrumenting the client to understand it, write a report/skill for future sessions etc

    you can also use the above to create a custom client or just a bot using web API. you can also easily break bot checks without puppeteered browsers now: "the above script aims to determine if it's executed on an allowed web browser, map out all its interactions with web browser APIs to fake adequate responses while using the Deno runtime". it's generally better to augment Deno to pass for Chrome and fool all the checks and their future versions then to just break a single check that may change soon.

    • pancomplex 1 day ago
      This works for non-authenticated sites but wouldn't work for anything behind a login wall that requires a JWT or similar - right?
      • teravor 1 day ago
        are you asking if it will magically allow you to bypass authentication? only if the service is vulnerable to auth bypass and you don't mind breaking multiple laws.
        • hahahaa 23 hours ago
          Or solve by allowing mcp to drive already authed session (using a legit user)?
  • ikuminw 1 day ago
    The self-updating recipe concept is good. Way better than maintaining hardcoded API specs that break every time the app updates.
  • west_subject 2 days ago
    Is this opensource ? like the tool itself ? in it's entirety ??
    • pancomplex 2 days ago
      Not at this point - but we’re considering it! What would you use it for?
      • Synthetic7346 2 days ago
        Gas and energy utility portal
      • west_subject 2 days ago
        make product demo videos, plus extend the functionality to save and contain repetitive task inside any app and have that run at some trigger.
  • robszumski 2 days ago
    Really cool. It would be interesting to see a demo of an app that is clearly more bespoke, like your Tesla account, online banking, movie theatre ticketing, etc.
  • zenniskayy 2 days ago
    Very cool project. Looking forward to trying it.
  • akash91 2 days ago
    Which LLM model is it using?
    • pancomplex 1 day ago
      Works with any frontier LLM model
  • spzb 1 day ago
    You want me to run a closed source, LLM agent inside my browser with access to authenticated API endpoints ?! Thanks but no thanks.
    • pancomplex 1 day ago
      No definitely not!

      Our customers run the training on their own applications using a demo or staging environment. Then they install the in-app agent you see in the demos and turn on the tool calls they like. All the API calls are executed client side and never touches any of our servers.

    • katemaster009 1 day ago
      But maybe we if have more clarity on how it is working under the hood, then maybe we trust it. For me its kind of pattern - too many if's but's and maybe's on all the new tools i want to use.
  • Priyansh7 2 days ago
    Cool project
  • reaganhsu 2 days ago
    so cool!
  • dodobirdy 1 day ago
    Now this is something truly agentic.
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