ComparisonsOpenAPI / SDK generators

Katip vs OpenAPI generators

OpenAPI generators shine when the API contract is the source of truth for clients. Katip starts earlier: domain aggregates, use cases, architecture axes — then technology mapping (including NestJS).

When to choose which

Lean their way when…

You already have a stable OpenAPI and need multi-language SDKs
The pain is client drift and SDK release automation
Server architecture is owned elsewhere

Lean Katip when…

The domain model and architecture profile are still fluid or thrashing under agents
You need capability-aware constraints before endpoints exist
You generate server-side structure (modules, ports) not only clients

Difference matrix

Side-by-side comparison dimensions
Dimension	Typical them	Katip
SSOT layer	OpenAPI / HTTP contract	Domain + architecture YAML (pre-contract)
Typical output	Client SDKs, docs, CI regen	Validated model + NestJS structural skeleton
Architecture axes	Out of scope (by design)	First-class (topology × style × communication × presentation)
Agent control	Indirect (better clients)	Direct (model constrains generation)
Complement	Use after API design stabilizes	Use to stabilize domain before/while APIs form

Honesty gate

Katip does not replace Speakeasy, Fern, or OpenAPI Generator for multi-language clients.
We do not claim full OpenAPI round-trip or SDK release automation today.
A healthy stack can use both: Katip for domain/architecture, OpenAPI tools for clients.

Generate SDKs from OpenAPI when the contract is stable. Use Katip when the domain model must lead the architecture.

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