An installed app cannot always update at the same moment as its server. Plan how the backend will support older versions and what happens when a phone retries a request after losing its connection. These decisions affect reliability as much as endpoint design.
Use this checklist before estimating the mobile clients. For every endpoint and event, identify the user journey it serves, the authoritative data source, allowed actor, validation, failure behavior, and evidence needed to operate it. The goal is not a large API inventory; it is a small, explicit contract that remains safe under real device and network conditions.
Related service: Android & iOS Application development- 01Map the journey, states, actors, data, and completion condition.
- 02Assign a source of truth and owner to every important record.
- 03Define versioned API contracts, validation, errors, and permissions.
- 04Specify offline reads, writes, retries, conflicts, and duplicate protection.
- 05Threat-model the app, APIs, storage, integrations, and administrative paths.
- 06Add logs, metrics, traces, alerts, recovery, and support runbooks.
- 07Test normal, interrupted, unauthorized, duplicate, and degraded journeys.
SECTION 01
Define boundaries and authoritative data
Start with the system map: mobile apps, backend services, databases, identity provider, notifications, files, analytics, CRM or ERP, payment services, and administrative tools. Draw who can initiate each action and where the authoritative result is stored. Avoid copying records into multiple systems without a reconciliation rule.
A mobile-specific backend or backend-for-frontend can shape data for the device, combine downstream calls, and isolate clients from internal change. It should not silently become a second source of truth. Record which layer owns customer identity, orders, appointments, inventory, entitlements, documents, and audit events.
| Area | Decision to record | Failure question |
|---|---|---|
| Identity | Provider, session/token model, recovery, device and role rules. | Can a user continue safely when a token expires or a device is lost? |
| Domain data | Source of truth, allowed mutations, validation, history, and retention. | How are conflicts or partial writes detected and reconciled? |
| Files and media | Upload path, size/type limits, scanning, access, processing, and deletion. | Can an interrupted or duplicate upload be resumed without corrupting state? |
| Integrations | Direction, identity mapping, limits, retries, reconciliation, and owner. | What does the user see when the downstream system is unavailable? |
| Notifications | Trigger, preference, payload sensitivity, deep link, and delivery record. | What happens when delivery is delayed, duplicated, or opened on another device? |
| Administration | Who can inspect, correct, replay, suspend, or delete records. | Are privileged actions authorized, logged, and reversible where possible? |
SECTION 02
Write a versioned API contract
Define each operation's path or event, method, authentication, authorization, request and response schema, validation, status and error model, pagination, sorting, limits, side effects, idempotency behavior, and deprecation policy. An OpenAPI document can make HTTP contracts testable, but it does not replace the business rules and examples that explain meaning.
Return errors the app can handle without exposing internal details. Separate validation, authentication, authorization, conflict, rate-limit, unavailable, and unexpected failures. Give the client a stable error identifier, safe message, and correlation identifier where appropriate so support can connect a user report with backend evidence.
SECTION 03
Separate identity, permission, and data protection
Use established platform and identity-provider flows rather than embedding credentials in custom schemes. For public native apps using OAuth, the IETF's native-app guidance describes using an external user agent and protections appropriate to public clients. The backend must validate tokens, issuer, audience, expiry, and authorization for the requested resource and action.
Do not trust identifiers, roles, prices, entitlements, or workflow states sent by the app. Enforce object and function authorization server-side, validate inputs, limit requests, protect secrets, encrypt appropriate transport and storage, and keep sensitive data out of logs and push payloads. Review the mobile client against OWASP MASVS and remote services against an applicable web/API standard.
Least privilege
Issue only the scopes and record access required for the current role and action.
Object checks
Verify the actor may access the specific account, file, order, or job—not merely the endpoint.
Secret boundary
Treat shipped app code as inspectable; keep server credentials and privileged decisions on controlled services.
Audit evidence
Record consequential actions with actor, target, time, result, and a safe correlation path.
SECTION 04
Design offline, retry, and duplicate behavior
Mobile networks disappear, slow down, and switch while a user is working. Decide which reads use local data, how freshness is shown, which writes require connectivity, which can queue, and how pending work appears. Android's offline-first guidance emphasizes local and network data sources plus explicit synchronization; the same product questions apply across mobile platforms.
Retries can repeat side effects. Use idempotency keys or operation identifiers for actions such as creating an order, uploading evidence, booking a slot, or initiating a payment. Define conflict rules for concurrent edits, do not assume device clocks are authoritative, and give users a recovery path when automatic reconciliation is unsafe.
| Action | Possible strategy | Required control |
|---|---|---|
| Refresh reference data | Read local data, then refresh when connected. | Freshness state, cache policy, and safe schema migration. |
| Save a draft | Write locally and synchronize later. | Persistent queue, user-visible state, conflict and retry rules. |
| Book scarce inventory | Require an online authoritative confirmation. | Reservation expiry, duplicate protection, and a clear failed state. |
| Upload a large file | Resumable background transfer where supported. | Checksums, size/type limits, authorization, and orphan cleanup. |
| Financial action | Server-controlled, idempotent online operation. | Strong confirmation, audit evidence, reconciliation, and no blind retry. |
SECTION 05
Make the mobile journey observable
Measure an end-to-end outcome, not only server uptime. Connect app version, platform, safe device class, request correlation, downstream dependency, latency, error type, queue age, and completion state without collecting unnecessary personal data. Crash reporting cannot explain a valid request that repeatedly fails a business rule or integration.
Define service objectives for the journeys that matter, alert thresholds, escalation, and a runbook. Include dependency outages, notification failures, queue buildup, elevated authorization errors, expired credentials, capacity, and data reconciliation. Ensure a support person can find an affected transaction without asking the user to expose sensitive details.
- 01
Name the critical user and administrative journeys.
- 02
Add safe correlation across client, API, queue, and downstream services.
- 03
Record outcome, latency, error class, retry, and version dimensions.
- 04
Alert on sustained user impact rather than every isolated technical event.
- 05
Document mitigation, rollback, replay, reconciliation, and communication steps.
SECTION 06
Use one backend readiness checklist
Before a production mobile release, rehearse a new account, returning account, expired session, unauthorized record request, interrupted upload, duplicated submission, slow network, downstream outage, and unsupported old client. Test administrative correction and recovery with the same care as the normal mobile path.
Confirm production configuration, secrets, certificates, domains, backups, retention, capacity, dashboards, alerts, on-call ownership, vendor contacts, runbooks, and rollback. Keep seeded demo or review accounts isolated and remove temporary bypasses. The backend is ready when the team can detect, explain, and recover from failure—not only when endpoints return success in a staging environment.
SECTION 07
Frequently asked questions
Does every mobile app need a custom backend?
No. Some products can use a suitable managed backend or existing system API. The choice depends on business rules, data ownership, integrations, security, scale, offline behavior, portability, and who will operate the service.
Should mobile apps call a database directly?
A production app normally accesses controlled services rather than receiving direct database authority. The service layer enforces authorization, validation, business rules, rate limits, audit, and compatibility while keeping privileged credentials off the device.
How should a mobile API handle older app versions?
Define a compatibility and deprecation policy, avoid breaking supported clients, observe active versions, use additive changes where possible, and provide a controlled upgrade requirement when an old version can no longer operate safely.
What is the difference between authentication and authorization?
Authentication establishes who or what is making the request. Authorization decides whether that actor may perform the requested action on the specific resource. A valid login does not grant access to every object or operation.
PRIMARY REFERENCES
Sources and further reading
These references cover the standards, platforms, or published prices discussed in the guide. Worked examples and checklists are our editorial guidance.
- OAuth 2.0 for Native Apps (RFC 8252)Internet Engineering Task Force
- OpenAPI SpecificationOpenAPI Initiative
- Build an offline-first appAndroid Developers
- OWASP API Security ProjectOWASP Foundation
- OWASP Mobile Application Security Verification StandardOWASP Foundation
- Secure Software Development Framework (SP 800-218)National Institute of Standards and Technology
EDITORIAL METHOD
About this guide
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