The developer capability behind MB-820
MB-820 is aimed at Business Central developers who need to build and maintain extensions. The official outline includes AL objects and language, development tooling, deployment, architecture and integrations. Experience expressed as a number of years is not a substitute for those capabilities: a developer can work on a narrow customisation for a long time without practising testing, permissions or deployment.
Choose an extension with a real boundary
A useful practice project is a warranty register linked to sold items. Define what the extension owns, what remains in the base application and which events will connect them. Create a table and page, validation rules, a permission set and a small report or API surface. Use fictional records. Avoid changing standard behaviour simply because a direct edit seems faster; your design should explain how an upgrade can be applied without losing the extension.
Make AL objects and behaviour work together
Rebuild a small feature from a clean project rather than copying a completed sample. Trace when table validation, page interaction and codeunit logic run. Investigate event subscribers and extension mechanisms using the current documentation. For the warranty example, test an invalid date, a missing item and a duplicate reference. Decide which validations protect stored data and which only assist the user interface. An API call may not follow the same user-interface path.
Debug, test and diagnose integration errors
Add automated tests for the supported and rejected cases. Use the debugger to inspect a failure before changing several lines at once. For an integration, document authentication, permissions, payload fields, error responses and retry behaviour. A request that times out may already have created a record, so your example should explain how repeated requests avoid duplicate warranties. Log enough technical information for diagnosis without logging private customer data or credentials.
Prepare from the current outline
Map every official objective to a lab result or a written explanation. Allocate additional sessions to AL objects because they connect much of the developer work, while still covering installation, tools and integration. An experienced developer should begin with a diagnostic: identify unpractised product areas instead of repeating the easiest language exercises. Use the official assessment to check breadth, but investigate why an answer is appropriate before marking that objective complete.
Show maintainability, not just a working demo
Finish the portfolio with a short deployment note, dependency list, rollback approach and upgrade test. Explain the tradeoff you made between a page extension, an event-driven change and a separate service. A hiring manager can assess that evidence more meaningfully than a screenshot of a certificate alone. Before booking MB-820, verify the current title, objectives and booking availability on Microsoft Learn; a course completion badge is a different item from the proctored certification.
Official references
Certification requirements and programme terms can change. Use the issuer’s current page and your account to confirm details before applying or paying.