LLMs Meet API Catalogs: A Practical Path to Intelligent Integration

The core idea was brewing in my mind, but it was brought to life during a recent APIDAYS workshop. The session was led by a banking AI team, which integrated its API catalog with its LLMs. The idea was to use this approach in the absence of an enterprise MCP catalog, which was recently released.

Large enterprises often maintain an API catalog—a centralised registry of their REST, SOAP, and event-driven interfaces. Traditionally, these catalogs have been used for governance, discovery, and compliance.

But with the rise of Large Language Models (LLMs), a new integration pattern is emerging: rather than relying on a third-party MCP-style catalog, firms are directly linking LLMs to their existing API catalogs. This unlocks the ability for developers, analysts, or even business users to query, explore, and auto-generate integration flows in natural language.

Why This Matters

• Firms already have API catalogs (Apigee, Kong, MuleSoft Anypoint, or custom)

• LLMs can parse OpenAPI specs, understand endpoints, parameters and response schemas

• Integration scenarios accelerate: instead of manually browsing, users can ask: “How do I fetch open invoices for a given customer?” and get back the correct API and sample code

Integration Approach

1. Extracting APIs from the Catalog

   • Use Exchange APIs (e.g., MuleSoft Anypoint Exchange REST API) to pull OpenAPI specs

2. Normalizing API Specs

   • Convert to a standard JSON schema (endpoint, verb, input, output, auth)

3. Registering with an LLM

   • Store in a vector DB or structured index

   • Feed to an LLM so it can answer API-related queries in natural language

4. Generating Code

   • LLM returns pseudocode, SDK snippets, or workflow definitions

Usage

1. Developer Co-pilot: Ask: “How do I retrieve customer order history?” → LLM returns the right API and a Java snippet

2. Business Analyst Querying: Ask in plain English → Get the API name, description, and usage instructions

3. Workflow Generation: LLM suggests orchestration across multiple APIs (CRM + Payments + Notifications)

Example

The gist shows a sample registry code for an org's MuleSoft exchange APIs.

Comparison: LLM + API Catalog vs MCP Catalog

Aspect	MCP Catalog	LLM + API Catalog
Setup & Infra	Requires separate MCP servers, new infra	Reuses existing API catalog infrastructure
Dependencies	Third-party protocol, new runtime components	In-house development, minimal new stack
Security	Additional surface (tool poisoning, remote servers)	Security model already governed in catalog
Flexibility	Rich primitives (resources, prompts, tools)	Focused on APIs, pragmatic for enterprises
Time to Value	Longer — requires MCP integration and governance	Faster — immediate head start with current assets
Control	Vendor-ecosystem driven	Fully enterprise-owned and customizable

Verdict

Criteria	Best Option
Cost & Ownership	LLM + API Catalog
Security & Control	LLM + API Catalog
AI Readiness	Both viable, but MCP richer in primitives
Time-to-Value	LLM + API Catalog

Final Thoughts

If your organisation already maintains an API catalog, integrating it with an LLM offers a cost-effective, secure, and fast-start approach. MCP may bring richer primitives in the long term, but for most firms, leveraging existing assets delivers quicker ROI and avoids unnecessary dependencies.