A FastAPI backend built to run
real agentic workflows.
You are building an AI agentic cowork system on Next.js and FastAPI, and the backend needs to hold up under real agent orchestration, not just single shot API calls. I design and build the service layer, the model routing across your open source LLM stack, and the async infrastructure that keeps agent workflows reliable as usage grows, working inside your existing codebase and conventions from day one.
The failure modes that hit every agentic backend.
Different teams, same three failure modes once agents move from demo to production. Each one shows up quietly at first and gets expensive fast.
Agent workflows outgrow simple API calls
Single request and response endpoints break down once agents start chaining tool calls, retrying, and holding state across steps. Without a purpose built orchestration layer, that complexity ends up scattered across ad hoc scripts.
Open source LLMs add real infrastructure work
Self hosted or open weight models mean you own the routing, the fallback logic, and the latency tradeoffs that hosted APIs used to hide. Getting that wrong shows up as slow, inconsistent agent behavior in front of your users.
A new engineer can slow a moving team down
Bringing someone onto an early stage backend risks technical debt or duplicated effort if they are not matching your existing patterns from day one. The right hire should compound your team's velocity, not just add hours.
A backend that scales with agent complexity.
I build the FastAPI service layer underneath your Next.js frontend, structured around the actual shape of agentic work: async task queues, streaming responses, and a clean abstraction for tool calls and multi step reasoning. Open source LLMs get routed through a single interface, so you can swap models, run fallbacks, and benchmark providers without touching application code. Every endpoint ships with test coverage, structured logging, and error handling from day one, not bolted on after launch. State management for long running agent workflows lives in a dedicated layer, so retries, checkpoints, and partial failures are handled explicitly instead of silently swallowed. I work inside your existing repo and conventions from hour one, so the codebase reads like your team wrote it, not like a contractor's side project. The result is a backend that scales with agent complexity instead of fighting it.
What you get. Phase by phase.
Every phase ships with concrete deliverables you sign off on before the next begins. No vague "ongoing collaboration" hours, no mystery scope.
- Full audit of the existing Next.js and FastAPI codebase, conventions, and repo structure
- Backend architecture plan mapped to the agentic workflows you are building toward
- Local and staging environments configured to match production exactly
- Coding standards, linting, and CI checks aligned to your team's existing patterns
- FastAPI service layer built with clear domain boundaries and typed request and response models
- Authentication, rate limiting, and request validation wired in from the start
- Async task queue set up for long running agent operations
- Structured logging and error handling standardized across every endpoint
- Unified model interface so open source LLMs can be swapped without touching application code
- Fallback and retry logic for model timeouts, rate limits, and degraded responses
- Streaming response support wired through to the Next.js frontend
- Benchmarking harness to compare latency, cost, and quality across model options
- Multi step agent workflow engine with explicit checkpointing between tool calls
- Tool calling abstraction that keeps agent logic decoupled from individual model providers
- Retry and recovery logic for partial failures mid workflow
- Session and state persistence for long running or multi turn agent tasks
- Test coverage across core endpoints and orchestration logic, unit and integration
- Observability dashboards for latency, error rates, and model performance by route
- Documentation written for your team, not just for me, covering architecture decisions and tradeoffs
- Async availability for code review, pairing, and iteration as the system evolves
Four weeks. Foundation to live.
Each week ships a working deliverable. Click any week to see exactly what lands in your repo by Friday.
Deliverables this week
- Full audit of the existing Next.js and FastAPI codebase, conventions, and repo structure
- Backend architecture plan mapped to the agentic workflows you are building toward
- Local and staging environments configured to match production exactly
- Coding standards, linting, and CI checks aligned to your team's existing patterns
Deliverables this week
- FastAPI service layer built with clear domain boundaries and typed request and response models
- Authentication, rate limiting, and request validation wired in from the start
- Async task queue set up for long running agent operations
- Structured logging and error handling standardized across every endpoint
Deliverables this week
- Unified model interface so open source LLMs can be swapped without touching application code
- Fallback and retry logic for model timeouts, rate limits, and degraded responses
- Streaming response support wired through to the Next.js frontend
- Benchmarking harness to compare latency, cost, and quality across model options
Deliverables this week
- Multi step agent workflow engine with explicit checkpointing between tool calls
- Retry and recovery logic for partial failures mid workflow
- Test coverage and observability dashboards for latency, errors, and model performance
- Documentation and async availability for review and iteration as the system evolves
Let's build the backend that scales with you.
A quick call to walk through the architecture, talk through your current Next.js and FastAPI setup, and confirm scope against your agentic roadmap. Happy to walk through hourly commercials on the call.