Mobile application developer. I ship the surface people hold, then design the API so a payment can clear certification, a tax document can be accepted, and a receipt can still print when the network is the unreliable part.
Illustrated
A live trip on the phone. A charge the location resolves. These drawings are not the production screens. The Tricycall landing page is the surface I shipped.
01 — Contracts
A good API can be understood without the documentation. I settle the patterns before the first endpoint, then the samples below are how those patterns show up in systems I have shipped. None of them is a production endpoint.
The URL names the thing. The method names what you do with it.
POST /createOrder POST /v1/orders
Collection, then id, then what belongs to it. One casing, used everywhere.
/v1/orders/{id}/items
GET reads. POST creates. PUT replaces. PATCH changes part. DELETE removes. Repeating PUT, PATCH, or DELETE does nothing further.
The client should not get 200 and then hunt the body for a failure. 201 created. 202 accepted. 400 invalid. 404 missing.
A person reads the message. Software reads the code. Validation names the field that failed.
Filtering, paging, and sorting stay in the query. An action never hides there.
GET /users?action=delete GET /v1/orders?status=shipped
Adding a field is safe. Removing one, or changing the shape, needs a new version. /v1 keeps working while clients move.
camelCase in JSON. kebab-case in paths. ISO-8601 for dates. Learn one endpoint and the next one should feel expected.
The error, every time
Same three fields on every failure. If a value is wrong, the message says which field and why.
{
"code": "LOCATION_NOT_FOUND",
"message": "No location with id loc_14",
"status": 404
}Tricycall · Firebase
trips/{tripId}
{
"state": "searching",
"vehicle": "tricycle",
"pickup": { "lat": 14.5995, "lng": 120.9842 },
"dropoff": { "lat": 14.6091, "lng": 120.9918 },
"riderId": "r_1842",
"driverId": null
}Decision The trip is a resource, trips/{id}, not an action. I built the rider, driver, admin, and landing page alone, and all four read that one document. Four private copies would drift the moment the driver moved.
WalletPass · multi-processor
POST /v1/charges
Idempotency-Key: 7f3c-sample
Content-Type: application/json
{
"locationId": "loc_14",
"amount": 2500,
"currency": "USD",
"reference": "wp_4419"
}202 Accepted
{
"chargeId": "ch_1882",
"status": "pending"
}Decision The path is /v1/charges, not /createCharge. 202 means accepted, not finished. POST is not naturally idempotent, so the key makes a retry the same charge. The location still chooses Elavon, Cybersource, Portaldom, or Orkespay. The client never names the processor.
e-CF · sample
Fiscal document
Next action · sign
Dominican Republic · e-invoicing
POST /v1/fiscal-documents
{
"type": "e-CF",
"buyerTaxId": "SAMPLE",
"sequence": "SAMPLE-0001",
"lines": [
{ "description": "Service", "amount": 2500 }
]
}201 Created
{
"documentId": "fd_220",
"state": "draft",
"next": ["sign"]
}Decision POST /v1/fiscal-documents creates the resource. 201 is the result. Press the document: the state moves, and the response names the next action. A rejection uses the same error shape as everything else, and it names the field that failed. This sample is not a filing template.
Varsity · Apple Wallet & Google Wallet
POST /v1/passes
{
"platform": "apple",
"themeId": "varsity",
"location": "Location 25",
"balance": 15,
"points": 5,
"accountNumber": "3009904"
}201 Created
{
"passId": "ps_90",
"platform": "apple",
"balance": 15,
"points": 5
}Decision POST /v1/passes creates the resource. Platform and theme are fields, not a new path like /createApplePass. Apple Wallet and Google Wallet render the same intent, so a theme can change without a new app.
Kotlin · Epson SDK
DEVICE epson.ble.print
{
"transport": "ble",
"terminal": "castles-s1e4-pro",
"printer": "epson",
"copies": 1,
"lines": ["WALLET PASS", "TOTAL 25.00", "APPROVED"]
}Decision This one is not HTTP. The habit is the same: one named job, and a result you can read without a second protocol. Castles S1E4 PRO and Pax take the payment. Kotlin talks to the Epson SDK over Bluetooth Low Energy, because the receipt still has to print when the cloud is down.
02 — Systems
Work I led, built solo, or maintained. The hard part was never a screen. It was keeping the screen honest with everything behind it.
Intercard · backend and frontend
One wallet product, many locations, and a different payment processor behind each location. I maintained both sides of it through certification with Elavon, Cybersource, Portaldom, Orkespay, and others.
The app stays stable while a processor changes. A location resolves to an adapter. Charges are idempotent. Async results come back as a status the client can trust.
Thesis · Built solo
A GPS hailing app for tricycles. I built it alone in Flutter and Firebase as four products: the rider app, the driver app, an admin panel, and the landing page.
Matching, live location, and trip state had to stay coherent across all four. The map is the interface. The shared trip is the product.
Dominican Republic · Regulatory APIs
I created the APIs for tax and e-invoicing compliance. A fiscal document is not a form you save. It is a sequence the regulator will accept or reject.
The contract exposes state and the next legal action. Clients cannot skip signing, and a rejection has to be readable by the person who has to fix the document. Press the next action. A bad tax id comes back naming the field.
Next action · sign
Devices · Kotlin
I contributed to mobile payment terminals, including the Castles Technology S1E4 PRO and Pax devices. On the printer path I integrated Epson over Bluetooth Low Energy with the Epson SDK, in Kotlin.
A terminal and a printer fail differently. The payment can be approved and the receipt can still be the part that breaks. That path gets its own contract.
Third-party API
I did not build the consumer app. I provided the third-party API behind it, including Apple Wallet and Google Wallet passes whose themes are data.
Intercard · Debug, maintain, integrate, publish
The Edge mobile apps: a guest wallet, remote game service, and redemption inventory. I debug, maintain, integrate, and publish them.
School · Backend lead
Laravel API for the school library. The first contract other people had to build against.
Sample contract
Migration
Moved legacy ASP.NET web services onto .NET 6 so the integrations could keep running on a stack we could still change.
Legacy to .NET 6
Gordon College · Next.js
A web app for checking graduation status. The page is the product.
Demo site
A marketing demo: marina berths, rooms, dining, events, and membership.
Freelance · Next.js
A Next.js project-management app with time tracking. The real screen is private. This is the admin: projects, tasks, and status.
Private app
03 — Stack
Listed because a system on this page depended on it. No scores, no filler.
Drag the top card, or click it.
04 — Path
The projects are already in the record. McDonald's is six months beside Gordon College, not the next stop after it. The line splits, then comes back to main.
git commit -m The development cycle as a company actually runs it. Azure tickets, a release process, and the work of making, integrating, fixing, and shipping apps that have to stay reliable. The role is mobile. The larger gain is software engineering: communication, corporate practice, and AI used in the work.
git commit -m Installed and kept up what a ship runs on. VSAT, ECDIS, networks, PCs, internet, and Cisco. The link has to hold when the next port is the only help coming.
git commit -m Six months on the floor, in parallel with Gordon College. A station can be clear enough that someone new, even a child, can run the whole thing. I still use that test. A good flowchart, and a clear architecture, is what lets other people run the system.
git commit -m The root commit. Basics, fundamentals, and a guided path into software engineering. The McDonald's branch leaves from here and comes back before the next commit on main.
05 — Contact
Certification, a flaky radio, a regulator, a driver on a map. Write the system you need built. It opens a note addressed to me.
Ralph Angelo Jaminal · Mobile application developer