Building APIs for Developers and AI Agents

Stainless founder Alex Rattray joins a16z partner Jennifer Li to talk about the future of APIs, SDKs, and the rise of MCP (Model Context Protocol). Drawing on his experience at Stripe—where he helped redesign API docs and built code-generation systems—Alex explains why the SDK is the API for most developers, and why high-quality, idiomatic libraries are essential not just for humans, but now for AI agents as well.

They dive into:

• The evolution of SDK generation and lessons from building at scale inside Stripe.
• Why MCP reframes APIs as interfaces for large language models.
• The challenges of designing tools and docs for both developers and AI agents.
• How context limits, dynamic tool generation, and documentation shape agent usability.
• The future of developer platforms in an era where “every company is an API company.”

Timecodes: 

0:00 – Introduction: APIs as the Dendrites of the Internet

1:49 – Building API Platforms: Lessons from Stripe

3:03 – SDKs: The Developer’s Interface

6:16 – The MCP Model: APIs for AI Agents

9:23 – Designing for LLMs and AI Users

13:08 – Solving Context Window Challenges

16:57 – The Importance of Strongly Typed SDKs

21:07 – The Future of API and Agent Experience

24:45 – Lessons from Leading API Companies

26:14 – Outro and Disclaimers

Resources: 

Find Alex on X: https://x.com/rattrayalex

Find Jennifer on X: https://x.com/JenniferHli

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Please note that the content here is for informational purposes only; should NOT be taken as legal, business, tax, or investment advice or be used to evaluate any investment or security; and is not directed at any investors or potential investors in any a16z fund. a16z and its affiliates may maintain investments in the companies discussed. For more details please see a16z.com/disclosures.

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