Founder Spotlight: Siebly — Better Crypto API Infrastructure

*Featured Founder Series — AI Tools Capital*

Winner of Week 13 of The Capital

Every week, The Capital highlights three startups chosen by the community. This week, Siebly Crypto API Prompt Framework took the **#1 spot with 18 votes**.

But Siebly is more than this week's winner.

Behind the product is a team that has spent years building infrastructure for developers working with cryptocurrency exchange APIs, helping make complex trading integrations easier, more reliable, and easier to build with.

We spoke with the team behind Siebly about the problem they're solving, what inspired the Crypto API Prompt Framework, the challenges of working with constantly evolving exchanges, and what's coming next.

What Is Siebly?

Siebly.io builds and maintains professional Node.js, JavaScript, and TypeScript SDKs for leading cryptocurrency exchange REST APIs and WebSockets.

The SDKs have been trusted for almost a decade by thousands of systematic trading systems worldwide.

Building connected algorithmic trading systems is already complicated. Developers shouldn't also have to spend their time dealing with the plumbing around authentication, requests, exchange-specific APIs, WebSockets, and integration details.

Siebly's SDKs provide a stable foundation developers can build on, allowing them to focus on their systems rather than the complexities of connecting everything together.

What Is the Siebly Crypto API Prompt Framework?

The Siebly Crypto API Prompt Framework was created around a growing challenge in modern software development: AI coding agents are becoming increasingly capable, but getting them to build complex systems correctly still isn't always straightforward.

As the founder explains, agentic coding gives people the ability to build sophisticated systems through conversations with tools such as Codex or Claude Code.

But common workflows in systematic trading can still trip these agents up.

Some architectures should be relatively simple and reusable, yet AI can sometimes overcomplicate or redesign REST-heavy workflows. That can result in unnecessary development time, repeated bugs, and flawed design decisions.

The Prompt Framework is designed as a resource for those situations. It provides ready-to-follow recipes and best practices for working with cryptocurrency APIs, helping coding agents start from proven patterns rather than reinventing the architecture from scratch.

> "The goal is simple: give the coding agent a better starting point."

If you build with agents across other stacks too, our AI coding tools category covers the wider ecosystem Siebly plugs into.

What Inspired the Framework?

One example is **account state management**.

A basic workflow might involve subscribing to account WebSockets to monitor changes, while using the REST API only when necessary to retrieve the current state.

Once configured correctly, WebSocket updates can maintain a local copy of account information such as orders, balances, and positions.

That local state can then act as a reliable source of truth with little or no latency, without constantly querying REST APIs before latency-sensitive actions such as order submission.

According to Siebly, this is just one of many examples where a straightforward architecture can become unnecessarily complicated.

Rather than hoping an AI coding agent gets the architecture right on the first attempt, the Prompt Framework provides a discoverable resource containing recipes that guide the agent from the beginning.

Who Is It Built For?

The Siebly SDKs have almost a decade of usage behind them.

The Siebly Crypto AI Prompt Framework, meanwhile, is designed for both aspiring and experienced algorithmic traders who want to work with crypto exchange APIs using coding agents.

Have an idea you'd like to automate? The framework can be used alongside a prompt generator, or developers can give the framework's URL to their preferred coding agent and ask it to build from the provided guidance.

What Makes Siebly Different?

The Crypto API Prompt Framework isn't simply another crypto API. It's a library of tooling and best practices designed to help coding agents avoid creating unnecessarily complicated or flawed integrations.

Crypto APIs also vary significantly between exchanges and even between different product groups on the same exchange, such as spot and futures.

Instead of repeatedly rebuilding the integration layer, developers can use battle-tested SDKs and frameworks to handle the underlying complexity.

That can mean less time spent rebuilding infrastructure and more time spent building the actual trading system.

A Feature Siebly Is Particularly Proud Of

One of the standout parts of the framework is its collection of **pre-made recipes**.

These recipes cover common workflows that systems are likely to need and have gone through significant testing. Some are detailed enough to help developers build a working project from the beginning.

Siebly is also particularly proud of the **WebSocket API integration** across its SDKs.

The core SDKs are hand-made and follow strict design controls designed to handle the demands of mid- to high-frequency trading systems. The WebSocket layer wraps an asynchronous, event-driven workflow in a REST-like interface, making it easier for developers — including AI coding agents — to work with.

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The Biggest Challenge: Crypto APIs Keep Changing

The cryptocurrency industry is still relatively young and exchanges are constantly evolving.

Different exchanges have different approaches to REST APIs and WebSockets, while documentation doesn't always perfectly reflect the reality of working with those APIs.

When integrating a new exchange, Siebly works closely with the exchange's API team to ensure the core workflows behave as expected. The result is connectivity that users can access without having to solve the same integration problems themselves.

The SDKs are also continuously tested and actively used by thousands of users.

4 Million NPM Downloads and Growing

One of Siebly's biggest milestones came this year when its public SDKs crossed 4 million downloads on NPM.

The company currently has 10 and counting public SDKs, with usage growing quickly. The team continues to improve the SDKs and supporting tooling every week.

What's Next for Siebly?

The team recently released another addition to its SDK family: the Node.js, JavaScript and TypeScript SDK for **HTX**, formerly known as Huobi.

But that's not the end of the roadmap.

Siebly's next release is expected to be its first public release for a **DEX** — something the team says has been requested many times by users.

So there's plenty more to come.

Where Can You Learn More?

🏆 The Capital Week 13 Champion

Congratulations to the Siebly team on the win — and thank you for taking the time to give us a look behind the product.

The Capital is a weekly community competition where AI startups compete for a place in the Top 3 and earn visibility, recognition, and a permanent place in the Capital's history.

🏆 Congratulations, Siebly.

Sources & Further Reading

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