API development & integration

Documented, secure APIs and integrations that move data reliably between your systems and partners.

Custom Software Development

openapi.yamldocs

1openapi: 3.2.02info: { title: Booking API, version: 1.4.0 }3paths:4  /appointments:5    get:  { summary: List appointments }6    post: { summary: Book an appointment }7  /appointments/{id}:8    get:    { summary: Get an appointment }9    delete: { summary: Cancel an appointment }

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What we build

Integrations we build

We design, build and run APIs and integrations that move data reliably between your systems, partners and apps, documented and monitored.

System integration
Sync customers, orders, invoices and stock between CRM, ERP, finance and line-of-business systems.
Partner and public APIs
APIs for customers and partners, with keys, rate limits, documentation and a developer portal.
Mobile and web backends
APIs that serve your apps, designed around the screens that use them.
Event-driven integration
Webhooks and message queues so systems react to changes as they happen.
Payment integration
Stripe, Adyen or PayPal connected to your checkout, invoicing and finance systems.
Third-party integrations
CRM, ERP, shipping, HR and marketing platforms connected through their APIs.

Fibre optic cables connected to a network switch

How to get started

Three steps to a plan for API development and integration

1Tell us what you needUse the project form or book a call. A few sentences about the goal is enough to start.
2Free technical consultationWe go through your goals, users, existing systems and constraints with you.
3Your planA detailed plan covering the right tech stack, architecture, timeline and budget. Then you decide.

Start a project Ask a question first

How it works

Four kinds of API we build

Fetching an appointment as REST, GraphQL, gRPC or a webhook event. Switch to compare the request, the response and when we use each.

Request

1GET /appointments/582132Authorization: Bearer eyJhbGciOi…

Response 200

1{ "id": 58213, "time": "2026-10-13T10:30",2  "dentist": { "id": 7, "name": "Dr Okafor" } }

Resources and HTTP verbs, described in OpenAPI. The default for public and partner APIs: cacheable and widely understood.

The life of a secure request

One booking request as a distributed trace, from gateway to database and events. Choose a span to see what happened in it.

trace 4bf92f35 · POST /appointments · 212 ms

auth · verify JWT · OAuth 2.0 access token verified against the identity provider's public keys; scope appointments:write checked.

Traces like this come from OpenTelemetry instrumentation, viewed in tools such as Grafana Tempo, Jaeger or Datadog.

Services

API development and integration services

Take one on its own, or combine them in one engagement with one team.

API design and development
REST, GraphQL or gRPC APIs, built from an OpenAPI or AsyncAPI contract agreed first.
Third-party integration
Connections to the platforms you use, with data mapping, retries and error handling.
API security and management
OAuth 2.0, rate limiting, an API gateway and a developer portal.
Integration support
Monitoring, alerts, fixes and new versions after launch.

Our approach

How the work runs

Each stage hands its output to the next, like the stages of a delivery pipeline.

Stage 1
Map the data
Systems, data owners, volumes, and which system is the source of truth for each field.
Stage 2
Design the contract
An OpenAPI or AsyncAPI specification, reviewed before any code is written.
Stage 3
Build and secure
Authentication, authorization, validation and rate limiting, tested against the contract.
Stage 4
Handle failure
Retries with backoff, idempotency, dead-letter queues and alerts.
Stage 5
Document and monitor
Developer documentation, versioning policy and dashboards for latency and errors.

What we'll need from you

Having these ready keeps the work moving.

System owners
People who know each system's data and can approve access.
Credentials and sandboxes
API keys and test environments for each system.
Vendor contacts
Support contacts for third-party systems, for integration questions.
An integration owner
Someone to receive alerts and take over after handover.

Who's on the project

Our team, working with system owners from yours.

ComponentOwner

Integration architect: Maps data, owners and patterns, and designs the contracts.

Deliverables

What you receive

Everything is handed over in your name: code, accounts and documentation.

Handed over

OpenAPI or AsyncAPI specifications

What the documentation looks like

Every project ends with documents your team can run with. Here is an excerpt of one of them.

openapi.yamlPreview

Orders API, v1

Reviewed with consumers before build

openapi: 3.2.0
paths:
  /v1/orders:
    post:
      summary: Create an order
      security: [{ oauth2: [orders.write] }]
      parameters:
        - in: header
          name: Idempotency-Key
          required: true
      responses:
        "201": { description: Order created }
        "400": { description: Invalid input }
        "429": { description: Rate limit exceeded }

Measuring success

How success is measured

What we report on in API development and integration projects. Which measures apply, and their targets, are agreed with you at the start.

GET /api/health/slos

{

"measures": Response time for 95% of requests, which shows the slow tail that averages hide.
},

}

Latency, by percentile

We set API objectives on percentiles, not averages. Move the threshold to see which share of requests meets it.

latency · POST /appointments · last 1,000 requests

0 ms360 ms+

Latency threshold200 ms

p50

48 ms

p95

92 ms

p99

283 ms

98.2% of requests under 200 ms. Misses a 99% SLO.

Averages hide the slow tail that users feel. SLOs are set on percentiles, such as 99% of requests under 300 ms.

Readiness check

Are you ready for
API development and integration?

Five questions, about a minute. You'll see what to settle first and a sensible starting point.

npx mayrian readiness --for "API development & integration"

? Do you know which systems need to exchange which data? (y / n / ?)

How to start

From first call to production

Start where you are. Each step ends with a decision, so you commit to the next one only when it makes sense.

git log --oneline --decorate

git show v0.1

Free technical consultation

Talk through the goal, the users, the systems involved and any deadlines.

+ A clear view of scope and priorities
+ A recommended next step
+ A plan covering stack, architecture, timeline and budget

Book the consultation

Estimate the value

What it could be worth to you

Enter your own figures. The formula is shown, and the estimate can go with your enquiry.

estimate.yaml

# Re-keying removed by integration

records_rekeyed_by_hand:# Records re-keyed by hand a monthminutes_per_record:# Minutes per recordloaded_cost_per_hour:# Loaded cost per hour

# formula: Records × minutes each ÷ 60 × hourly cost

$ mayrian estimate

Re-keying time saved

$7,000

a month

1# => $7,000 a month

Add to my enquiry

Build or buy

When you don't need
a custom build

Part of the free technical consultation: when an existing product covers the need, we recommend it instead of a custom build. These are the options we weigh, alongside the tools you already have.

When: new appointment

Then: find or create contact in CRM

Then: create invoice in ERP

An automation tool may be enough

Automation tools such as Zapier or Make: when simple, low-volume flows between SaaS tools with ready-made connectors.
Native connectors between your platforms: when your SaaS vendors already offer a supported integration for the data you need.

Technologies and standards

Chosen for your project

Gateways manage traffic; specifications define the contract. Choose a gateway to see what it offers.

Open source and enterprise gateway with plugins for auth, rate limiting and transformations.

Contracts first

OpenAPI 3.2REST APIs
AsyncAPI 3.1Events and messaging
GraphQL SDLGraphQL schemas
Protocol BuffersgRPC services

Our technology radar for API development and integration

Adopt Trial Assess Caution

techniques / adopt

Architecture decision records

A short record of each significant decision, its context and its consequences, kept in the repository.

Our default. We use it on client projects unless there's a reason not to.

Our recommendations. Updated September 2026.

Styles

REST
GraphQL
gRPC
Webhooks

Specifications

OpenAPI
AsyncAPI
JSON Schema

Integration platforms

MuleSoft
Boomi
Azure Integration Services
Apache Kafka

Security

OAuth 2.0
OpenID Connect
OWASP API Security Top 10
mTLS

In your industry

Where it applies

What this work delivers in the industries we serve.

Questions

Common questions
about API development and integration

Do you build REST or GraphQL APIs?

Both. We build REST for most integrations and public APIs, since it's easy to cache, and GraphQL for apps that need flexible queries across related data.

Do you work with integration platforms?

Yes. We build on MuleSoft, Boomi or Azure Integration Services when you have many integrations and a team to run them, and write lighter custom integrations when you have a handful.

How do you keep APIs secure?

With OAuth 2.0 or API keys scoped to what each consumer needs, input validation, rate limiting and tests against the OWASP API Security Top 10.

How is a project priced?

Well-defined scopes are delivered as fixed-price engagements; when requirements are still evolving, we provide a dedicated team instead. Either way, the free technical consultation ends with a plan covering tech stack, architecture, timeline and budget, so you know the cost before work starts.

API development & integration

Integrations we build

System integration

Partner and public APIs

Mobile and web backends

Event-driven integration

Payment integration

Third-party integrations

Three steps to a plan for API development and integration

Four kinds of API we build

The life of a secure request

API development and integration services

API design and development

Third-party integration

API security and management

Integration support

How the work runs

Map the data

Design the contract

Build and secure

Handle failure

Document and monitor