What happens if a provider changes or removes the endpoint we depend on?

Each provider sits behind its own adapter with contract tests recorded from that provider, so a retired version or a renamed field usually touches one module. We watch provider changelogs and deprecation notices for the services you run on, and you get a written note with the impact and the hours involved. Updates go to staging first and are released on your schedule.

Can you build the work without access to our production data?

Yes, and we prefer it. Most integrations are built and tested in the provider's sandbox with test credentials, and calls are recorded once and replayed as fixtures afterwards. Where no sandbox exists we test against a mock that follows the published contract, and staging runs on synthetic records.

How do you stop a retry from creating a duplicate order or charge?

Writes accept an idempotency key, and the server stores the key with the result, so a repeated request returns the original outcome instead of creating a second record. Unique constraints in the database enforce the same rule, and a scheduled reconciliation compares our records against the provider's side.

We already have an integration that another developer built. Can you take it over?

Yes. We start with an audit of the authentication, the retry behaviour, the error handling and the tests, then tell you which parts are safe to keep. Recorded contract tests are usually added before any code changes, so we can see a regression the moment it appears.

Do you document the API for our own developers or partners?

The reference is generated from the same specification the server validates against, so it cannot fall out of step with the code. We add runnable examples, an error code table, a changelog, an importable Postman or Bruno collection, and a recorded walkthrough of the authentication flow.

API Development & Integration

REST and GraphQL API development and third-party integrations, covering authentication, versioning, idempotency, rate limits, webhooks and retries.

See our work:

Automated Sales Workflow: Real Estate Case Study→Big Mail Project→Vasilkoff.info - AI Project Estimator & Chat Support Web App→

Any product that talks to another company's software inherits that company's roadmap decisions. A payment provider retires an API version after three months of notice. A CRM renames a field. Your integration keeps working until the day it does not, and the first signal is often a customer saying an order never appeared.

That exposure shrinks when the connection layer is engineered on its own terms: versioned contracts, provider responses recorded as tests, queues that hold work during an outage, and alerts that name the provider.

What this service covers

One kind of work here is a custom API you own: REST or GraphQL endpoints so a mobile app, a partner or an internal tool can read and write your data against a documented contract. The other connects systems you already run, such as payments in Stripe, CRM records in HubSpot or Salesforce, messaging over Twilio or WhatsApp Business, and model calls to OpenAI or Anthropic.

What decides whether either holds up is authentication, repeated calls, and the gap between a provider failing and a person noticing.

Who it is for

Product teams shipping a mobile app or partner portal that needs one documented API
Operations teams where staff copy records between two systems by hand every morning
Companies whose vendor integration demoed well and now times out under real traffic
Teams that inherited an integration and have no test environment for it
Teams adding AI features that need the provider call, the key and the rate limit handled on the server (see secure AI backend and API key protection)

What we deliver

The contract and access

We write the contract before the code: an OpenAPI specification for REST with endpoints, request and response shapes, status codes and one consistent error format, or a GraphQL schema capped by query depth and complexity. Authentication uses OAuth2 client credentials, scoped API keys or short-lived tokens issued per client, so one partner's access is revoked on its own. Credentials live in a server-side secret store, since a key in a browser bundle gets scraped.

Versioning and idempotency

A public API gets a version from day one, in the path (/v1/orders) or in a header, and changes stay additive where clients allow it. A breaking change means a new version, a deprecation window and a note to the clients affected. Writes accept an idempotency key that the server stores with its outcome, so a client retrying after a timeout receives the original result instead of creating a second charge. Unique constraints and reconciliation against the provider's records back that up.

Rate limits, retries and webhooks

Requests pass through a queue with a token bucket per provider, honour the Retry-After header on a 429 response, and batch or cache where the provider permits it, with per-tenant quotas so one client cannot spend the whole allowance. Failed calls retry with exponential backoff and jitter. Inbound webhooks are verified by signature before parsing, acknowledged inside the provider's timeout and processed asynchronously, with handling keyed on the event id because providers resend. A replay tool reprocesses an event after a fix.

Error handling and observability

Errors are typed, so validation, authentication, rate limits, provider faults and timeouts each take a different path. Every outbound call logs a correlation id, latency and outcome, so one order can be traced across systems, and work that cannot complete lands in a dead-letter queue with its payload attached.

Documentation and safe testing

The reference is generated from the specification the server validates against, so it cannot drift, and it ships with runnable examples, an error code table, a changelog and an importable Postman or Bruno collection. Integrations are built in sandbox mode with test credentials, never against real customer records. Provider responses are recorded once and replayed as fixtures, where no sandbox exists a mock enforces the published contract, and staging uses synthetic records with email, SMS and payment captures switched off.

When a third-party API changes or fails

An announced breaking change, such as a retired version or a new authentication requirement, arrives in the provider's changelog or as a deprecation email. Each provider sits behind its own adapter with recorded contract tests, so the update touches one module, and you get a short note covering what changed and the hours involved.

An unannounced payload change is caught by response validation. A response that stops matching the expected shape fails in a controlled place instead of writing a half-filled record, the alert names the provider and the operation, and the work waits in the queue.

A provider outage trips timeouts and a circuit breaker. Retries use backoff with jitter, the queue holds the work instead of dropping it, and reconciliation checks both sides for anything lost once service resumes. A rate limit change arrives as a 429, which the queue already understands, and a usage alert fires before the plan ceiling is reached. Token expiry is refreshed centrally, with a reminder before a key lapses.

If a provider withdraws a feature entirely, the adapter leaves room for a second implementation behind the same interface, and a feature flag moves traffic across. When a webhook never arrives, the reconciliation sweep re-queues records that exist on the provider's side and not on ours. Vendors change their APIs on their own schedules, so detection, isolation and recovery are the parts we design.

How an engagement runs

Discovery takes one to two weeks: we read the provider documentation, obtain sandbox credentials, decide which system owns each field, and list the failure cases worth designing for. The output is a written contract and a scoped first release.

Build runs in two-week cycles, each ending on a staging URL you can call.

Hardening covers load testing the queue, alert thresholds, the replay tool and an incident runbook. Handover gives you the specification, the collection, the environment variables and a recorded walkthrough. One integration usually lands in two to five weeks; a programme connecting several providers runs six to twelve weeks.

What it costs

Work runs at our flat rate of $39 per hour against a written scope, or under the monthly capacity plans from $2,699 for teams with a steady stream of integration work. The Vasilkoff pricing page sets out both models and what each one suits.

Scope drivers are countable: how many providers are involved, whether sandbox access exists, how much provider documentation is out of date, whether historical data has to be reconciled, whether an OAuth application has to be reviewed, and whether the codebase needs an audit first. Payment work adds compliance questions, which the payment gateway integration service covers.

Proof

Vasilkoff.info is our own AI estimator and chat application, built in Next.js with domain-tuned logic and intake output shaped into a predictable structure. The same conversational capability ships as embeddable widgets in Vanilla JS and React, which shows an API consumed by more than one front end.

The Big Mail Project moved postcard sending online on Laravel, Node.js, React and Next.js with MongoDB and MySQL behind it, including the integration work that carried an order from a web form to a delivered product.

The automated sales workflow receives Instagram messages through a webhook into PostgreSQL in n8n, generates replies with OpenAI against stored conversation history, holds sensitive replies for Gmail approval and schedules follow-ups by stage. It is the clearest example we have of a webhook pipeline where a dropped message costs a deal.

Related services

Web development for the platform work that surrounds an API
AI development when the integration connects a model provider or an automation pipeline
Database design and migration for the schema, indexes and data moves behind the endpoints
Payment gateway integration for card payments, subscriptions, refunds and payouts
Secure AI backend and API key protection for moving provider calls and secrets off the browser

Next step

Send the list of providers you need to connect, with any documentation or credentials you hold. We will say which parts are straightforward, which need a sandbox first, and what the first release should contain.