Why "no throwaway prototype" works with Claude Code

The PoC that survives contact with the MVP

Most proofs of concept get built, demoed, and then quietly deleted. The team learns something useful, the stakeholders nod, and then a separate project starts from a blank repository to build the real thing. The PoC was throwaway by design, and everyone treats that as normal.

I think it is normal because of one specific failure, not because PoCs are inherently disposable. Most PoCs never define a stable contract between the front end and the back end. They wire a UI directly to whatever shortcut got the demo working, and that shortcut is exactly what cannot survive into production.

On a recent engagement I joined as Solutions Architect on a greenfield UK education-sector platform. By the end of week one I had a runnable Vue.js front end and a matching C# backend-for-frontend in front of the team, fed by a deliberately stupid mock service layer. The team built directly on that codebase for the next three months. The MVP that shipped was the same codebase the PoC started as. There was no rebuild.

This post is about why that worked, and the small number of cases where it would not.

Why traditional PoCs end up in the bin

A traditional PoC optimises for one thing: getting something on screen quickly so a stakeholder can react to it. That is a legitimate goal. The problem is the shortcuts that get you there.

Hard-coded data lives inside components. API calls are stubbed inline next to the rendering code. The shape of the data the UI consumes is whatever the developer happened to type that afternoon, and it is implicit, undocumented, and entangled with presentation logic.

When the real backend work begins, none of that survives. The back-end team designs proper services, picks proper field names, normalises properly, and the front end has to be rewritten to match. The PoC was useful as a conversation, but as code it was a dead end.

The diagnosis is straightforward. The PoC never had a contract. It had a vibe.

Contract-first as the inversion

The alternative is to define what the front end needs from the back end as the first artefact, before any real implementation exists on either side. Endpoints, request shapes, response shapes, error semantics, pagination, the lot. Treat that contract as the deliverable of discovery.

Then back it with a mock service layer that returns canned responses for every endpoint. No database, no queues, no business logic, no I/O. The mock exists to satisfy the contract and nothing more.

The front end is built against the mock. The back-end team builds real services that satisfy the same contract. As real services come online, the mock for that endpoint is retired and the front end keeps working without modification, because it was always coded against the contract, not against the mock.

The PoC and the MVP are not two codebases. They are the same codebase at two different points along a curve.

Why Claude Code makes the contract-first step cheap

Contract-first sounds obvious when you describe it. The reason teams do not do it is that producing a usable contract has historically been weeks of meetings, whiteboards, and revisions. By the time you have a real contract, the stakeholder has lost interest and someone has already built a hard-coded prototype to keep the conversation alive.

This is the bit AI-augmented discovery changes, and specifically the part Claude Code accelerates. I can take a set of design screenshots, walk through them with the team, and produce a component library, a route map, and a draft data contract in one pass. The contract is not perfect, but it is concrete enough to argue with, which is what you actually need.

A junior or mid-level developer cannot easily produce a coherent contract from a set of screens. Claude Code can produce a draft, and a Solutions Architect can shape and correct it in hours rather than weeks. That is the cost reduction that makes contract-first practical on a real engagement budget.

End of week one, on the engagement I described, the team had:

• A Vue.js front end rendering real screens.
• A C# backend-for-frontend exposing every endpoint the front end called.
• A mock service layer behind the BFF returning canned responses.
• A documented contract that everyone, technical and non-technical, could read.

That last point matters. Operations directors and product owners could look at the contract and tell me what was missing, because the contract was expressed in terms of the business, not in terms of database tables.

What the mock layer actually looks like

People sometimes assume the mock layer is sophisticated. It is the opposite. It is deliberately stupid, and the stupidity is the feature.

A mock endpoint for a learner progress query returns the same five learner records every time. A mock endpoint for a submission status returns "submitted" for half the IDs and "pending" for the rest, based on a modulo. A mock endpoint for a document upload returns success and a fabricated identifier. There is no persistence, no validation, no authorisation logic.

The reason this matters is that the mock has to be obviously a mock. The moment you start adding logic, two things happen. The mock starts behaving like a real service, which means bugs in the mock are confused with bugs in the front end. And the team starts depending on mock behaviour that the real back end will not replicate, which reintroduces the rewrite you were trying to avoid.

A good mock returns canned data with the correct shape and the correct status codes. Nothing else. If you find yourself writing a switch statement inside the mock, stop and ask whether that logic belongs in the real service.

How the contract carries the team

Once the contract and the mock exist, the social dynamics of the project change in ways that are easy to underestimate.

The front-end developers can work at full speed without waiting for the back-end team. They have a stable surface to code against. When they discover a missing field or an awkward shape, they raise it as a contract change, the change is agreed, the mock is updated, and work continues. The back-end team is not blocking, because the back-end team has not started yet.

Junior developers benefit disproportionately. A junior front-end developer struggling against a half-built real backend spends most of their time guessing whether a bug is theirs or someone else's. A junior developer working against a deterministic mock can isolate their own work and ship.

The back-end team, when they start, are not designing in a vacuum. They have a contract that has already been pressure-tested by real UI work. They know which fields are actually used, which endpoints are called frequently, and which response shapes the front end finds awkward. That is information you would normally only get after the first painful integration.

The hinge moment: retiring the mock in stages

The transition from PoC to MVP is the part most teams get wrong, because they treat it as a single event. It is not. It is a sequence.

On the engagement, the mock layer was retired one endpoint at a time as real services came online. Each real endpoint was deployed behind the same contract, the mock for that endpoint was switched off, and the front end carried on rendering. Some endpoints were live within weeks. Others stayed mocked for the full three months until the real implementation was ready.

At no point was there a "cutover day". At no point did the front end need to be rewritten. The MVP that shipped was the codebase the team had been working in since week one, with progressively more of it backed by real services and progressively less by canned responses.

This is the property that makes contract-first economically interesting. The throwaway phase that usually sits between PoC and MVP simply does not exist.

When this approach does not work

I want to be honest about the boundary, because this pattern is not universal.

If your PoC exists to disprove a hypothesis, you are in a different situation. A research prototype that asks "can we get acceptable progress-engine performance on this data shape at this volume?" is not trying to become an MVP. It is trying to give you a yes or no. Optimising it for survival is wasted effort, and you should expect to throw the code away.

The same applies if the PoC and the MVP genuinely have different requirements. If the PoC is a single-tenant demo and the MVP is a multi-tenant SaaS with completely different security and data isolation needs, the contract you would design for one is not the contract you would design for the other. Pretending otherwise just produces a contract that fits neither.

The contract-first pattern works when the PoC and the MVP are aiming at the same target, and the PoC's job is to make that target visible early. That covers most commercial product engagements I see, but it does not cover all of them.

The combination is what matters

Contract-first design is not a new idea. People have been writing about it for as long as there have been APIs. The reason it has not been the default is cost. Producing a usable contract from a fuzzy product idea has historically required senior people, lots of meetings, and weeks of elapsed time, which is exactly what early-stage product work cannot afford.

AI-augmented discovery using Claude Code changes the cost curve. Producing a draft contract from design screenshots and a conversation is now an afternoon's work for a Solutions Architect, not a fortnight's work for a team. That is what makes contract-first viable as the default rather than the exception.

Either ingredient on its own is not enough. AI-augmented discovery without a contract still produces a throwaway PoC, just faster. A contract-first discipline without AI assistance is still affordable only on engagements with the budget for it. The combination is what lets a one-week PoC turn into a three-month MVP without a rewrite.

If you are about to start a build and the default plan is a throwaway PoC followed by a separate MVP project, it is worth a conversation about whether you actually need that gap. Often you do not.

If that resonates and you want to talk it through against your specific situation, I am happy to have a chat.