Ship your API MVP in 3 weeks
REST or GraphQL APIs (think: the plumbing that lets two apps talk to each other), clear documentation, rate limiting, webhooks, and a full developer portal — built and live in 21 days, starting from £8,000.
Most developer tool startups spend months debating architecture instead of shipping. We compress that cycle. We arrive at your scoping session with proven API templates. We lock a written contract on Day 1. We hand you a working API with ready-made code kits (SDKs) and a self-serve developer portal before the month is out. If you want to understand what an MVP is and why starting small saves you money, that guide is worth three minutes of your time.
3 weeks
Delivery timeline
REST/GraphQL
OpenAPI spec included
Dev portal
Docs + keys + sandbox
£8k
Starting price
Why API-first startups stall before they ship
An API is like a waiter in a restaurant. Your app (the customer) sends an order. The API (the waiter) passes it to the kitchen (your database or service) and brings back the result. Building that waiter sounds simple. In practice it is harder to plan than a full website. Without a clear written contract upfront, teams waste weeks bolting on security, usage limits, and error handling to an API that was built as a quick fix. By the time other developers try to connect their apps, they hit missing fields and confusing rules that only make sense to the person who wrote the code.
The second problem is the documentation gap. Engineers build a working API and then treat the instructions as something to write later. Without a practice area (sandbox) and a live reference guide, early users give up before they ever make their first successful call. Research from Stripe and Twilio shows that the speed of that first successful call is the single strongest sign of whether a developer becomes a paying customer.
We eliminate both problems. We start with contract design — a single written spec (called an OpenAPI 3.1 document) is the source of truth for everything that follows. The reference guide, code kits, test server, and validation rules are all created from that spec automatically. They stay in sync as your product grows. The result is an minimum viable product that another developer can connect to in an afternoon, not a week. Working with an MVP development agency that has done this before cuts your risk even further.
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Everything in your API MVP
Every project covers the full API product surface — not just the endpoints (the individual actions the API can perform). Here is what ships in 3 weeks.
REST or GraphQL API
Fully typed endpoints built with Node.js/TypeScript or Python FastAPI. REST is like ordering from a fixed menu — simple and reliable. GraphQL is like a custom order — flexible but more complex. We pick the right fit for your product on Day 1.
OpenAPI Documentation
A live, clickable guide generated directly from the API spec. Developers can try any endpoint in the browser, see exactly what to send and what they get back, and copy ready-made code examples in five languages — no guessing required.
API Key Management with Scopes
Self-serve key creation with permission levels (read-only, write, admin). Keys are stored securely (hashed, never readable), work in test or live mode, and can be turned off instantly from the developer portal or your admin panel.
Rate Limiting & Throttling
Think of rate limiting like a speed bump. Each key gets a request allowance per minute based on their plan (e.g. Free: 100 calls/min, Pro: 1,000 calls/min). When they go over, they get a clear error with instructions on when to try again. You can adjust limits without any code changes.
Webhook Delivery
Webhooks are automatic notifications — like a text message your API sends to your customer's app when something happens (a payment completes, a file finishes processing). We build secure delivery with automatic retries and a log your customers can check themselves.
Developer Portal & Sandbox
A branded website where developers sign up, grab their API key, read the docs, and test calls against fake data — all without touching your live product. The goal: from sign-up to first successful call in under 10 minutes.
BUILD IT FAST
Ready to ship your API in 3 weeks?
Book a free 30-minute scoping call and get a fixed-price quote within 48 hours. No retainers, no hidden fees.
TALK TO A FOUNDER
Not sure where to start?
Book a 20-minute call. We'll map out your scope, tech stack, and go-to-market plan — for free.
How we build your API MVP
We break the work into 5 clear steps over 21 days. Each step has a defined output so you always know where we are. This is the same approach we use for our startup MVP development and B2B SaaS MVP projects.
- 01
API Contract Design (Days 1–3)
A half-day session produces a full written spec: what resources exist, what each endpoint does, how login works, what errors look like, and how versions are handled. This spec is saved in your code repository and becomes the single source of truth. A test server and request checker are auto-generated the same day — so you can try calls before a single line of real code is written.
- 02
Core Endpoint Build (Days 4–10)
We build all endpoints against the spec. Every request is validated. Every error response follows a consistent format so developers know exactly what went wrong. Login security (OAuth 2.0 or API key) is wired in with permission levels. Every endpoint gets automated tests that run on every code save.
- 03
Rate Limiting, Webhooks & Security (Days 8–14)
Usage limits go live on a test server with your plan tiers configured. The webhook pipeline is built: events fire, queue up for delivery, retry on failure, and carry a security signature so your customers can verify the message is really from you. Security headers, cross-origin rules, and input checks are reviewed and locked.
- 04
Developer Portal & Sandbox (Days 12–18)
The developer portal launches on a test web address with interactive docs, key management, usage charts, and a sandbox (a safe practice environment with dummy data). You click through the entire developer journey and give feedback. Code kits for Node.js and Python are generated from the spec and published to a private package registry.
- 05
Launch Prep & Handover (Days 19–21)
Live infrastructure is set up (containerised on AWS or Railway). The automated pipeline runs tests, packages the code, and deploys on every code merge. Final code kits are published to npm and PyPI (the public package stores). You receive a complete handover pack: architecture diagram, runbook, environment variables list, and a recorded walkthrough video.
Who builds an API MVP with Greta?
Most of our API clients fall into one of three groups. First, founders building a developer tool — something other engineers will pay to use, like a data enrichment API, a messaging service, or a payments wrapper. Second, B2B software teams who need to open their platform to outside developers or partner companies. Third, startups that have a working product and now need to offer a SaaS product layer on top so customers can automate their workflows.
In all three cases the challenge is the same: building the API correctly the first time, so you are not rewriting it six months later. Our AI MVP development work also involves building APIs — most AI products are an intelligent API under the hood. If your product uses an AI model, we can scope both the AI layer and the API wrapper in the same 3-week engagement.
Not sure if your idea qualifies? Book a free call and we will tell you honestly within 30 minutes whether a 3-week build is realistic or whether you need a longer engagement.
How Greta compares — API MVP options in 2026
There are several ways to build an MVP API. Here is how each option stacks up on cost, speed, and ongoing support.
| Option | Cost | Timeline | Support |
|---|---|---|---|
| Traditional agency | £80,000–£200,000 | 6–12 months | Extra cost |
| Freelancer | £20,000–£60,000 | 3–9 months | You manage it |
| No-code tools | £0–£500/month | Weeks | Very limited |
| Greta | From £8,000 | 3 weeks | Included |
BUILD IT FAST
Get a fixed-price API MVP quote
Share your API concept and we will respond with a scope, timeline, and price within 48 hours — no commitment required.
TALK TO A FOUNDER
Not sure where to start?
Book a 20-minute call. We'll map out your scope, tech stack, and go-to-market plan — for free.
Do you need a dashboard on top of your API?
Many API products need a visual layer too. Your customers want to see their usage numbers, errors, and account settings in a screen — not just raw data. We build these as part of the developer portal, or as a separate admin interface if you need more depth.
If you need a full custom dashboard — charts, filters, team management, export features — we scope that as an add-on or a separate engagement. Many clients start with the API MVP, get their first paying customers, and then commission the reporting dashboard in the following sprint. That way you are building what users actually ask for, not what you guessed they would want.
If you are building a software-as-a-service MVP where the API and the dashboard are one product, we can scope both together. The 3-week timeline applies to a focused API scope. Adding a full SaaS frontend typically extends the build to 5–6 weeks. We will be clear about that in your first call — no surprises. Speak to our team to get a clear scope for your specific product.
Frequently asked questions about API MVP development
Can you really build a production-ready API MVP in 3 weeks?+
Yes — for a well-scoped API product. The key is arriving at Week 1 with a clear problem statement and data model. We run a half-day contract design session on Day 1, lock the OpenAPI spec by Day 3, and build in two-week sprints with daily async stand-ups. Our API-first templates and CI/CD foundations mean we spend time on your unique business logic, not boilerplate. Complex integrations or legacy system migrations may require an extended 5–6 week engagement.
REST or GraphQL — which should my API MVP use?+
For most developer tool MVPs, REST with OpenAPI documentation is the right default. It is easier to cache, simpler to document, and has broader tooling support. We recommend GraphQL when your clients need highly flexible querying across interconnected data — think content APIs or internal tooling with many consumer teams. We are experienced in both and will recommend the best fit for your use case during scoping.
What authentication approach do you use for API keys?+
We implement HMAC-signed API keys with configurable permission scopes (read, write, admin) stored as hashed values in your database — never in plain text. Keys can be namespaced by environment (test vs. live), rotated on demand, and revoked instantly. For APIs that also serve browser-based clients we layer OAuth 2.0 PKCE on top. Enterprise customers often need SSO/SAML integration, which we scope as a post-MVP add-on.
How does rate limiting work in the MVP?+
We implement a sliding-window rate limiter backed by Redis. Each API key is assigned a tier (e.g. Free: 100 req/min, Pro: 1,000 req/min, Enterprise: custom) and limits are enforced at the API gateway level before requests hit your application logic. Standard 429 responses include Retry-After and X-RateLimit-* headers so integrating developers can handle limits gracefully. Tiers are configurable in your admin panel without a code change.
What is included in the developer portal you build?+
The developer portal includes: interactive API reference documentation generated from your OpenAPI spec, self-service API key creation and management, per-key usage analytics (requests, errors, latency), a sandbox environment with seed data, code samples in multiple languages, a changelog, and webhook configuration UI. It is a standalone Next.js application deployed to Vercel or your own infrastructure, with your branding applied.
Sources & further reading
External references cited on this page.
OpenAPI Initiative — OpenAPI Specification 3.1
The official OpenAPI 3.1 specification that underpins every API contract Greta authors. Maintained by the Linux Foundation.
Postman State of the API Report 2024 — API adoption trends
Annual industry survey covering API-first adoption, developer experience priorities, and time-to-integration benchmarks across 40,000 developers.
OWASP API Security Top 10
The definitive reference for API security risks — authentication flaws, broken object-level authorisation, rate limiting gaps — that Greta audits against in every build.
Stripe Engineering Blog — Designing robust and predictable APIs
Stripe's canonical guidance on idempotency keys, error handling, versioning, and webhook reliability — patterns Greta implements by default.
Related services
MVP Development Agency
End-to-end MVP builds for any product type in 3–6 weeks.
SaaS MVP Agency
Full-stack SaaS platforms with billing, auth, and admin panels.
AI MVP Development
LLM-powered products, RAG pipelines, and AI APIs shipped fast.
B2B SaaS MVP
Multi-tenant SaaS with role-based access and usage metering.
Dashboard Development
Real-time analytics dashboards that sit on top of your API data.
Startup MVP Development
Fast, founder-focused MVP builds to validate before raising.
Your API could be live in 21 days
Stop going in circles on architecture documents and start getting developers connected. We will define your API contract, confirm the scope, and send you a fixed price within 48 hours of your call. No retainers. No surprises. Build your MVP with an agency that has shipped over a dozen API products in the last 12 months.
Free 30-minute discovery call. Real pricing within 48 hours.