---
type: concept
title: "Contract-First Development"
description: "Define the shared interface or data contract between an agent's frontend, backend, and collaborating agents before building either side, so components can be developed independently and wired together reliably."
tags: [contracts, interfaces, full-stack-agents, agent-teams, api-design]
videos: [coding-agent-reliability-explodes-when-they-argue-new-adversarial-dev-technique, how-to-properly-use-claude-code-agent-teams-full-live-build, claude-codes-agent-teams-are-insane-multiple-ai-agents-coding-together-in-real-time, ai-agents-can-now-build-their-own-ui-in-real-time-personalized-to-you, build-a-rag-ai-agent-with-real-time-source-validation-copilotkit-pydantic-ai, insane-new-strategy-for-building-ai-agent-apps, build-a-full-stack-app-for-your-n8n-ai-agent-in-20-minutes]
created: 2026-07-21
updated: 2026-07-21
---

# Contract-First Development

Contract-first development means agreeing on the interface between components before writing either side of it. As Cole describes his command, "my command implements what I call a contract first approach. The lead agent defines the contracts between the front end, backend, and database," and the reason is coordination without collision: "they can work in parallel, but they still have that sort of coordination defined up front." The sequencing is deliberate, "Define the contracts, map that before you start spinning up all of the agents... it's only step five where we actually spawn all the agents in parallel."

The contract is what unblocks parallelism. Cole calls the technique "contract first spawning. So we're not doing everything in parallel. We're setting the stage up front for some of that work that has to be done before we can just kick off all the agents like here's our database schema for example." Critically, a contract is a promise, not a finished component: an agent's "first job is to build the database layer and then send me its contract. So it doesn't have to be done done. It just has to send the contract, then it can spin up the backend agent." That handoff is enough for downstream agents to start.

The same discipline appears between a frontend and backend. In generative-UI builds, "we have this sort of contract between the backend and the front end... Here are all of the different components that you can render," with matching type definitions on both ends: "all of the types defined in our backend... is exactly the same as the types that we have defined in the front end." Cole names the shared state directly: "the state is really a contract that we have between the front end and back end with AGUI... Same structure, same types, same everything." Adversarial-agent workflows push it further, having the generator and evaluator "negotiate a contract" before any code: "here are the different phases... and here's how we're going to evaluate each phase... they're agreeing on what that battle looks like up front."

## Prerequisites

- [Planning with AI](./planning-with-ai.md) - the contract is defined during the up-front planning phase.
- [Phases of Work](./phases-of-work.md) - contracts partition a spec into phases that can proceed independently.

## Part of

- [Agent Teams](./agent-teams.md) and [Parallel Agentic Coding](./parallel-agentic-coding.md) - contracts are what let multiple agents work concurrently without conflict.

## Related

- [Generative UI](./generative-ui.md) and [Agentic Experiences](./agentic-experiences.md) - front/back contracts naming renderable components and their props.
- [Chat Interfaces](./chat-interfaces.md) - shared request/response state between UI and agent.
- [Adversarial Agents](./adversarial-agents.md) - generator and evaluator negotiate a contract before building.
- [Deterministic Workflows](./deterministic-workflows.md) - a fixed contract makes handoffs predictable.
- [Reduce Assumptions](./reduce-assumptions.md) - an explicit contract removes cross-component guesswork.
- [Stacking Context-Engineering Strategies](./strategy-stacking.md) and [Validation](./validation.md) - contracts as a layer that later validation checks against.

## Tools

- [Claude Code](../entities/tools/claude-code.md) - runs the lead agent that defines contracts before spawning the team.
- [AG-UI](../entities/tools/ag-ui.md) and [CopilotKit](../entities/tools/copilotkit.md) - carry the typed state contract between frontend and backend.
- [Pydantic AI](../entities/tools/pydantic-ai.md) - defines backend types that mirror the frontend contract.

## Sources

- [How to Properly Use Claude Code Agent Teams (FULL LIVE BUILD)](../sources/how-to-properly-use-claude-code-agent-teams-full-live-build.md) - "[0:31:37] my command implements what I call a contract first approach. The lead agent defines the contracts between the front end, backend, and database."
- [Claude Code's Agent Teams Are Insane](../sources/claude-codes-agent-teams-are-insane-multiple-ai-agents-coding-together-in-real-time.md) - "[0:18:12] its first job is to build the database layer and then send me its contract. So it doesn't have to be done done. It just has to send the contract, then it can spin up the backend agent."
- [Coding Agent Reliability EXPLODES When They Argue](../sources/coding-agent-reliability-explodes-when-they-argue-new-adversarial-dev-technique.md) - "[0:09:52] before we go into writing a single line of code, we're actually going to have the generator and evaluator negotiate a contract."
- [AI Agents Can Now Build Their Own UI in Real Time](../sources/ai-agents-can-now-build-their-own-ui-in-real-time-personalized-to-you.md) - "[0:12:00] we have this sort of contract between the backend and the front end. So we're giving the agent options. Here are all of the different components that you can render."
- [Build a RAG AI Agent with REAL-TIME Source Validation (CopilotKit + Pydantic AI)](../sources/build-a-rag-ai-agent-with-real-time-source-validation-copilotkit-pydantic-ai.md) - "[0:11:10] the state is really a contract that we have between the front end and back end with AGUI... Same structure, same types, same everything."
- [INSANE New Strategy for Building AI Agent Apps](../sources/insane-new-strategy-for-building-ai-agent-apps.md) - "[0:02:46] this really teaches us best practices about turning our agent into an API endpoint so that we can hook it into any front end."
- [Build a FULL Stack App for your n8n AI Agent in 20 Minutes](../sources/build-a-full-stack-app-for-your-n8n-ai-agent-in-20-minutes.md) - "[0:03:23] I have to tell Claude that there's a output key from the response Json and that's what contains what I get back from the llm that I need to display back out to the user."
