How LLMs Are Breaking the API Contract (And Why That Matters) - API Developer Weekly

API Developer Weekly Sept 18, 2025 - Issue #560 This week we look at how LLMs are breaking the API contract, the new api-catalog RFC, and API mocks vs simulation. We also look at how microservices are slower than in-process method/function calls (shock face goes here), how the APIs we worked so hard to design are now legacy when it comes to AI agents, and a local SFO meetup about MCP servers. Finally, there is a new MCP registry (and expect more to come if history is any indicator, along with meta registries for those registries - stand up yours today!), an update from the AsyncAPI team, and a spotlight on API security including recent vulnerabilities due to client-side hashes, lack of input validation (check those POST parameters, kids!), and Cloudflare DDOSing itself due to a misplaced API call with a react hook. -- Happy Reading! Featured Articles How LLMs Are Breaking the API Contract (And Why That Matters) LLMs often break API contracts, posing risks for security and governance. Here's how to prepare APIs for safe agentic consumption. by Art Anthony [nordicapis.com] Exploring api-catalog, a New API Discovery Standard RFC 9727's api-catalog offers a standard way to make APIs discoverable for tools and AI, but its success depends on broad adoption. by Kristopher Sandoval [nordicapis.com] API Mock vs. Simulation What is the difference between an API mock and a simulation, and why does that matter? by Bruno Pedro [apichangelog.substack.com] I Replaced Our Microservices With a Monolith - It's Somehow Faster I Replaced Our Microservices With a Monolith - It's Somehow Faster A year ago, our backend looked like a maze. We had split everything into microservices because that's what everyone seemed to ... by Observability Guy [observabilityguy.medium.com] Why Your Legacy APIs Are a Roadblock for AI Agents Discover why legacy APIs built for humans are failing AI agents and learn the technical and cultural shifts needed to create effective, AI-ready API specs. by Saqib Jan [thenewstack.io] MCP Server Builder Series Events related to helping developers build MCP servers. Check out this event series if you live in or will be visiting San Francisco in the coming weeks. [luma.com] Introducing the MCP Registry Today, we're launching the Model Context Protocol (MCP) Registry-an open catalog and API for publicly available MCP servers to improve discoverability and implementation. By standardizing how servers are distributed and discovered, we're expanding their reach while making it easier for clients to get connected. The MCP Registry is now available in preview. by David Soria Parra (Lead Maintainer), Adam Jones (Registry Maintainer), Tadas Antanavicius (Registry Maintainer), Toby Padilla (Registry Maintainer), Theodora Chu (MCP PM at Anthropic) [blog.modelcontextprotocol.io] AsyncAPI Monthly Community Update: August 2025 AsyncAPI community and project updates for August 2025 [asyncapi.com] Spotlight on API Security A deep dive into Cloudflare's September 12, 2025 dashboard and API outage Cloudflare's Dashboard and a set of related APIs were unavailable or partially available for an hour starting on Sep 12, 17:57 UTC. The outage did not affect the serving of cached files via the Cloudflare CDN or other security features at the Cloudflare Edge. [blog.cloudflare.com] Manipulating India's Stock Market: The GST Portal Data Leak Manipulating India's Stock Market: The GST Portal Data Leak Imagine if you could peek into the books of India's biggest companies - before quarterly earnings were announced. By simply looking ... by Aseem Shrey (@aseemshrey) [aseem-shrey.medium.com] Frostbyte10 bugs put grocery refrigeration devices at risk Major flaws uncovered in Copeland controllers: Patch now [theregister.com] (Un)Related API-First Architecture: Building Scalable Systems for the Modern Era Software ArchitectureAPI-First Architecture: Building Scalable Systems for the Modern Era A comprehensive guide to understanding, implementing, and scaling API-first design principles Introduction In ... by Kennedy Owusu [medium.com] So You Want to Develop a MCP Server? So You Want to Develop a MCP Server? So you are able to develop your MCP server? Wait a second, isn't there millions of MCP servers already? Since there is already millions sample projects LLM can ... by Liangjun Jiang [liangjunjiang.medium.com] SOLID is killing the micro-services industry - ADAPT saves it. SOLID is killing the micro-services industry - ADAPT saves it. For years SOLID architecture has been the norms for software design and architecture. From the 00's it doesn't reflects anymore a ... by Mathieu [medium.com] Building a web search engine from scratch in two months with 3 billion neural embeddings End-to-end deep dive of the project, spanning a large GPU cluster, distributed RocksDB, and terabytes of sharded HNSW. by Wilson Lin [blog.wilsonl.in] Vibe Coding is Creating a Generation of Unemployable Developers | HackerNoon Vibe coding lets AI generate code-but skips the skills that make developers indispensable. Learn why shortcuts can ruin careers in 2025 tech. [hackernoon.com] Upcoming Events API Economy Summit / London "Beyond the hype. Making commercial sense of the API Economy" Featuring Caroline McIntyre and Stephen Haynes, both Natwest September 22, 12-5pm Details and registration (Contact Claire Barrett for more details) Platform Summit 2025 Engineer next-gen API architectures Oct 13-15 Stockholm, Sweden Discount code: ps25-apidvwk - good for 15% off any ticket until Oct 15, whether for the full conference, the half-day API Security UnConference, or a bundle. Tickets and registration API Economy Summit / Melbourne "Turning API Economy aspirations into realities for people and teams" Headliners TBA October 30, 10am-3:30pm Details and registration (Contact Claire Barrett for more details) apidays Amsterdam Explores how APIs are the foundation of enterprise GenAI readiness. November 6, 2025 Amsterdam, Netherlands Details and registration apidays Paris API governance, monetization, and future trends December 9–11, 2025 Paris, France Details and registration API Economy Summit / Paris "Powering the API Economy" Headliners TBA December 10, 10am-4pm Details and registration (Contact Bertrand Masson) Have something to share? As always, if you want to chat, share a link, or make a suggestion, feel free to drop us a quick note or tagging us on Twitter (@launchany and @caseysoftware) or by emailing us at: james@launchany.com. Want to change how you receive these emails? You can update your preferences or unsubscribe from this list.