Fastapi Vs. Devii: When To Write An Api Vs. Generate One

FASTAPI is a Python framework for building REST APIs by hand. You define endpoints in Python, hook them up to a database, validate inputs, return responses. It's flexible. It's well-documented. Coding agents write FastAPI very well — it was a v1 recommendation and remains one.

Use FastAPI when:

• Your API needs custom business logic that doesn't map cleanly to "read/write rows from a database."
• You have unusual auth requirements, complex permissions, or multi-step workflows.
• You want to learn how APIs work, not just use one.
• The agent is going to write most of it for you and you just need to review.

DEVII is a different beast. It's a paid service ($49/month starting, free first month) that connects directly to your SQL database (PostgreSQL, MySQL, Oracle, others) and instantly generates a GraphQL API on top of it. You don't write API code. You don't define endpoints. You don't write authentication. Devii does it.

The selling points:

• Auto-generated schema from your database tables.
• Built-in policy-based access control (PBAC) for permissions.
• Process rules for things like email sending, PDF generation, payment processing — common backend tasks you'd otherwise have to write.
• Deterministic, not probabilistic. The schema generation is rule- based, not LLM-based, which means it doesn't hallucinate columns.

Use Devii when:

• You're not going to write the API yourself, and you don't want to babysit an agent that's writing one.
• Your application is mostly "read and write rows from a database with permissions" — the 80% case for small business apps, dashboards, internal tools.
• You need an API working today and you'll iterate on the frontend while the API just exists in the background.

The honest comparison:

If you're a v1 graduate who can read and write FastAPI, the FastAPI-with-an-agent path is fine, and you save $49/month. If you've never written an API before and you're going to be vibe coding the frontend anyway, Devii saves you the cognitive load of pretending to care about backend work you don't want to do.

For most readers in groups 2 and 3 from section 0.4 (small business owners, idea-havers), Devii is the right pick.

For readers in group 1 who already finished v1, the FastAPI path is familiar and you might prefer it.