Custom Guestline integration development
Appfront builds custom Guestline integrations that connect your Rezlynx PMS in real time with your booking engine, channel manager, CRM or own application. Through the Guestline API we synchronise reservations, room availability, rates, guest profiles and payments, so your team no longer has to retype anything and guests see the same up-to-date information everywhere.
What is a Guestline integration?
Guestline is a hospitality software provider whose core product is the cloud-based Rezlynx PMS (Property Management System). Around it, Guestline offers a channel manager, distribution hub, booking engine and payments, all built around a single central source of availability and reservations. Hotels, hotel groups and serviced apartments use Rezlynx to manage the front desk, front office, rates and guest data.
In practice, a custom integration means synchronising reservations and bookings both ways between Rezlynx and your own or third-party systems, keeping room availability and rates up to date, exchanging guest profiles with your CRM or check-in flow, and making sure payments and invoicing align neatly with the PMS, without manual retyping or duplicate administration.
Appfront builds on the official Guestline developer documentation and the OWASP ASVS security standard. Guestline works with the hospitality standards HTNG and OTA and applies an onboarding and certification process for API integrations. We align data flows, business logic and error handling with your actual property processes, so the integration grows with your organisation and remains reliable even at peak occupancy.
Reservations in sync
Bookings from your booking engine or channel manager land automatically in Rezlynx, and changes made in the PMS flow back. No double entry and no overbookings: availability and reservations stay consistent everywhere.
Availability & rates
Up-to-date room availability and rate plans are pushed from Rezlynx to your channels. Price changes, restrictions and allotments are correct everywhere within moments, so you don't lose revenue to outdated data.
Guest data & payments
Guest profiles, check-in data and payments connect neatly to your CRM, guest app or point-of-sale system. We handle payment data in line with PCI principles, so the guest experience runs smoothly and your accounts stay accurate.
Our development process for Guestline integrations
We work to a proven methodology that removes uncertainty early and delivers a stable integration. From an initial analysis of your property processes and Guestline onboarding through to go-live and ongoing management, every step aims at an integration your team can understand and trust.
We map out the data flows you need, such as reservations, availability, rates, guest profiles or payments, which systems run alongside Rezlynx, and which direction synchronisation should take.
We design the integration architecture, arrange the Guestline credentials and onboarding, choose a middleware layer where needed and define an error-handling strategy.
Implementation with automated tests, structured logging and monitoring, tested against the Guestline test environment and the certification process. You see working builds along the way.
Controlled go-live with data validation and a safety net, followed by ongoing management, monitoring and further development.
What a Guestline integration concretely delivers
Every Guestline integration is set up specifically for your property, your systems and the data flows that really matter. Below are the features we most often deliver for hotels and serviced apartments that use Rezlynx as their central PMS.
Guestline API & connect
A stable connection to the Guestline API in line with the HTNG and OTA standards. We handle the onboarding, credentials and certification process, and build the integration so that your own systems communicate with Rezlynx securely and reliably.
Reservations & bookings
Two-way synchronisation of reservations between Rezlynx and your booking engine, channel manager or own application. New bookings, changes and cancellations are processed immediately, so reception always works with up-to-date information.
Rooms, availability & rates
Room availability, rate plans, restrictions and allotments sync from Rezlynx to your channels. Price changes are reflected correctly everywhere, and you avoid overbookings or sales at outdated rates.
Guest profiles & check-in
Link guest profiles from Rezlynx to your CRM, guest app or online check-in. Preferences, stay history and contact details come along, so you can communicate in a personalised way and check-in runs smoothly.
Channel manager & distribution
Connection to distribution via OTAs and metasearch, such as Booking.com, Expedia and Agoda, so inventory is distributed live and bookings flow back into Rezlynx automatically. One source of truth for all your channels.
Payments & invoicing
We connect payments and in-stay charges neatly to the PMS and your accounting or point-of-sale system. Transactions, deposits and invoicing align with each other, with PCI principles for payment data and balanced accounts.
Typical use cases in practice
A Guestline integration looks very different from one organisation to the next. We see a number of recurring patterns, and for each of them we have a working set-up that pays close attention to reservations, availability, guest data and payments.
Independent hotel
An individual hotel that runs Rezlynx as its central PMS and wants its own booking engine, channel manager and payments kept in sync with it. Direct bookings via its own website, no overbookings and a reception team that always works with current data. See also our API integrations.
Hotel chain or group
A chain or group with multiple properties that wants central reporting, shared guest profiles and consistent data flows to its CRM and distribution. We build an integration that works consistently across all properties and connects to your middleware and back office.
Serviced apartments & B&Bs
Serviced apartments, aparthotels and B&Bs with longer stays and a strong focus on online check-in and self-service. Availability, length of stay, deposits and guest communication flow through the integration, so guests can check in and out smoothly without manual work at the front desk.
Restaurant & spa facilities
Hotels with a restaurant, bar or spa that want to connect their point-of-sale (POS) system and facility bookings to Rezlynx. In-stay charges for dinner, drinks or a spa treatment post automatically to the room account, so the guest folio is accurate and settling up at departure goes smoothly in one go.
Technology we use
We build Guestline integrations using the official Guestline API and the HTNG and OTA hospitality standards, combined with the backend stack that suits you. The exact choice depends on your surrounding systems and data flows, so your own team can manage or further develop the integration.
Why choose Appfront for your Guestline integration?
Appfront has extensive experience building API integrations for a wide range of organisations in the Netherlands. We always start with a thorough analysis of your existing systems and processes. An integration should not only work technically, but also add practical value to the way you work.
For every integration, we write clear documentation and make sure your own team, or any future supplier, can understand and manage it. No black box, just transparent code and clear agreements on monitoring, alerting and maintenance.
You work with a dedicated point of contact who understands both the technical and the functional side. This keeps communication short, prevents misunderstandings and speeds up decisions when choices need to be made during development.
See also our wider services around API integrations, middleware, custom software development and web app development.
- Experience with the Guestline API, the Rezlynx PMS and HTNG/OTA standards
- Specialists in integrations with booking engines, channel managers, CRM and POS
- Familiar with reservations, availability, guest profiles and payments
- Secure by default: credential rotation, data validation, scoped permissions
- Structured error handling and retry mechanisms
- Comprehensive logging and monitoring from day one
- Clear documentation your team can read and manage
- A fixed point of contact, no account managers passed around
- Ongoing maintenance and proactive further development
- A way of working aligned with your existing IT landscape
Security and privacy in Guestline integrations
Reservations and guest profiles always contain personal data, and payment flows touch sensitive card data. Appfront builds to the OWASP ASVS. That means, among other things: credentials kept in secure vaults, strict validation of incoming and outgoing data, scoped permissions per integration, and regular audits of the reservation and payment flows. We handle payment data in line with PCI principles and, where possible, keep it outside your own systems.
We document the data flows between Rezlynx and your surrounding systems so your record of processing activities is complete and you can demonstrate compliance with the GDPR. Through data minimisation, clear retention periods and traceable logging, you know exactly which guest data goes where and who has access to it.
More on our security approach: information security policy and CVD policy.
- GDPR-compliant data processing and data minimisation
- Encryption in transit (TLS 1.2+) and at rest
- Role-based access and least-privilege principles
- Audit logs with traceable data flows
- Automatic retries and dead-letter queues
- Monitoring and alerting for anomalies
- Secrets management in line with best practice
- Documentation for your record of processing activities
Frequently asked questions about Guestline integrations
Answers to the questions we get asked most often about Guestline integrations.
A Guestline integration is a technical link between Guestline Rezlynx PMS and another system, such as your booking engine, channel manager, CRM, point-of-sale system or own application. Through the Guestline API, reservations, room availability, rates, guest profiles and payments are exchanged between the systems. Guestline works with the HTNG and OTA hospitality standards. An integration can be simple (synchronising availability and rates) or extensive (two-way reservation sync, guest profiles, in-stay charges and payment handling).
A Guestline integration fits when you use Rezlynx as your central PMS and want surrounding systems, such as a booking engine, channel manager, CRM, POS or guest app, to stay in sync with it in real time. For simple, standalone scenarios, a standard interface from the Guestline marketplace is sometimes enough. As soon as you need custom logic, your own application or a non-standard data flow, we build a custom integration. Together with you, we look at which approach best fits your property and processes.
A simple integration, such as synchronising availability and rates between Rezlynx and a single external system, can go live within a few weeks. More advanced scenarios involving two-way reservation sync, guest profiles, in-stay charges and payment handling usually take longer, partly due to the certification process Guestline requires for API integrations. After an intake meeting, we will provide a realistic estimate.
We work with the official Guestline API and the hospitality standards HTNG and OTA, combined with the backend stack that suits you: Node.js, Python, PHP, .NET, Ruby or Go. Authentication and credentials are handled through the Guestline onboarding process. For reliable synchronisation, we implement a middleware layer where necessary, with retry mechanisms, queueing and structured logging, so that reservations and availability remain consistent even during peak volumes.
The cost depends on the complexity of the data flows, the number of systems to be integrated, the desired synchronisation frequency and the amount of custom business logic. The Guestline certification process, ongoing management, monitoring and support also affect the total investment. We always provide a clear quote following a no-obligation analysis of your situation.
Yes. Reservations and guest profiles contain personal data and payment data, so security is central. Appfront builds in line with the OWASP ASVS: credentials are held in secure vaults, incoming data is validated, permissions are scoped, and rights are strictly separated per integration. We document the data flows so your record of processing activities remains complete and you can demonstrate GDPR compliance. We handle payment data in line with PCI principles and, where possible, keep it outside your own systems.
Yes. Appfront regularly takes over existing integrations, even if they were originally set up by another party. We review the API integration, data flows, error handling and monitoring, document the current setup and propose improvements. From that point on, we can handle adjustments, extensions and ongoing management, including timely rotation of credentials.
Guestline and the Rezlynx PMS are used by independent hotels, hotel chains and groups, serviced apartments, B&Bs and wider hospitality organisations. An integration makes sense once you run several systems alongside your PMS, such as a booking engine, channel manager, CRM, restaurant or spa POS, or your own guest app, and you want availability, reservations and guest data to stay in real-time sync without manual re-entry.
Ready to build your Guestline integration?
Tell us which data flows you want to connect, such as reservations, availability, rates, guest profiles or payments, and which systems Rezlynx needs to work with. We are happy to help with the architecture, the Guestline onboarding process and reliable synchronisation. A no-obligation first conversation will give you a clear picture of the possibilities within half an hour. Or ask your question directly via contact.