Product Building Blocks

The features nearly every product needs, and the pitfalls hidden inside them.

Backend Engineer

Write correct code, ship small changes safely, ask good questions.

Core: start here

Double SubmissionA user clicking twice and creating two orders, and how to prevent it.

3 more junior concepts

Rounding and MoneyNever store money as a float; use integers or decimals.
Sign-Up and Email VerificationCreating accounts and confirming the user owns the email address.
Slugs and Readable URLsTurning titles into URL-safe identifiers, and handling duplicates and renames.

Own a feature end to end without hand-holding.

Approval WorkflowsMulti-step approvals modeled as explicit states and transitions.
Data ExportLetting users download their data, often as a background job.
Finite State MachineA model with a fixed set of states and allowed transitions, e.g. an order going from paid to shipped.
Password Reset FlowDesigning reset links that are single-use, short-lived and don't leak account existence.
Payments IntegrationUsing providers like Stripe safely, with webhooks and idempotency.
Record History and VersioningKeeping previous versions of rows with history tables or temporal tables.
Subscription BillingPlans, trials, renewals, failed payments and dunning.
Invoices and ReceiptsGenerating immutable, numbered billing documents.
Organizations, Teams and MembershipsModeling accounts that many users share, with roles per membership.
User-Facing Activity LogShowing users who changed what and when.
InvitationsInviting people into an organization or team with expiring, single-use links.
Account DeletionDeleting or anonymizing a user across every table and system.
Entitlements and Plan LimitsDeciding which features and quotas each plan unlocks.
Coupons and DiscountsPromotions without letting them stack or be abused.

Own a system, its failure modes, and its trade-offs.

Multi-TenancyServing many customers from one system while keeping their data apart.
Ledger and Double-Entry BookkeepingRecording money movements as balanced, append-only entries.
Inventory and ReservationsTemporarily holding stock or seats so two buyers can't get the last one.
Recurring EventsRepeating schedules, RRULE, and their time zone edge cases.
Sales Tax and VATCharging the right tax for each customer's location.
ProrationCharging fairly when a customer changes plans mid-cycle.
Usage MeteringCounting billable usage accurately, without double-counting.
Multi-Currency HandlingStoring, converting and displaying money in several currencies.

Build and fix pipelines from clear specs; write correct SQL.

Own pipelines and models end to end, including their quality.

Data ExportLetting users download their data, often as a background job.
Finite State MachineA model with a fixed set of states and allowed transitions, e.g. an order going from paid to shipped.
Record History and VersioningKeeping previous versions of rows with history tables or temporal tables.

Design the platform's storage, processing and modeling choices.

Ledger and Double-Entry BookkeepingRecording money movements as balanced, append-only entries.
Usage MeteringCounting billable usage accurately, without double-counting.

Build UI that works, ship small changes safely, ask good questions.

Core: start here

Double SubmissionA user clicking twice and creating two orders, and how to prevent it.

3 more junior concepts

Rounding and MoneyNever store money as a float; use integers or decimals.
Sign-Up and Email VerificationCreating accounts and confirming the user owns the email address.
Slugs and Readable URLsTurning titles into URL-safe identifiers, and handling duplicates and renames.

Own a feature end to end without hand-holding.

Approval WorkflowsMulti-step approvals modeled as explicit states and transitions.
Data ExportLetting users download their data, often as a background job.
Finite State MachineA model with a fixed set of states and allowed transitions, e.g. an order going from paid to shipped.
Password Reset FlowDesigning reset links that are single-use, short-lived and don't leak account existence.
Payments IntegrationUsing providers like Stripe safely, with webhooks and idempotency.
Subscription BillingPlans, trials, renewals, failed payments and dunning.
Organizations, Teams and MembershipsModeling accounts that many users share, with roles per membership.
User-Facing Activity LogShowing users who changed what and when.
InvitationsInviting people into an organization or team with expiring, single-use links.
Account DeletionDeleting or anonymizing a user across every table and system.
Entitlements and Plan LimitsDeciding which features and quotas each plan unlocks.

Own an app's architecture, performance, and failure modes.

Recurring EventsRepeating schedules, RRULE, and their time zone edge cases.
Multi-Currency HandlingStoring, converting and displaying money in several currencies.

Ship the smallest thing someone will use or pay for, and set up the company properly.

Subscription BillingPlans, trials, renewals, failed payments and dunning.
Invoices and ReceiptsGenerating immutable, numbered billing documents.
Multi-TenancyServing many customers from one system while keeping their data apart.

Get users who stay, pay and tell others; raise your first real round.

Account DeletionDeleting or anonymizing a user across every table and system.
Entitlements and Plan LimitsDeciding which features and quotas each plan unlocks.
Coupons and DiscountsPromotions without letting them stack or be abused.
Sales Tax and VATCharging the right tax for each customer's location.
ProrationCharging fairly when a customer changes plans mid-cycle.
Usage MeteringCounting billable usage accurately, without double-counting.

Make acquisition and revenue repeatable; hire, raise and build a board.

Multi-Currency HandlingStoring, converting and displaying money in several currencies.