APIs often have access to sensitive data, making it critical for organizations to know about every single API in use. Yet many companies struggle with shadow APIs and undocumented endpoints. You can’t protect what you can’t see, making comprehensive API visibility fundamental to any security program.
Effective API discovery requires a systematic approach that spans the entire software development lifecycle (SDLC). The following are seven essential API discovery best practices security teams should implement, from source code analysis to continuous monitoring.
1. Conduct source code analysis and repository scanning
Comprehensive API discovery begins at the source. Modern static application security testing tools automatically scan code repositories to identify API definitions, endpoints and configurations such as OpenAPI definitions.
Pay special attention to configuration files, environment variables and deployment scripts that might reference external APIs or define new endpoints. Many organizations discover forgotten APIs lurking in legacy codebases or experimental branches.
Tools to consider include the following:
- StackHawk’s API Discovery connects directly to code repositories, using an inside-out approach to discover APIs from source code with automated schema generation.
- Semgrep provides fast static analysis across most programming languages to find API patterns in code, making it an excellent open source option for identifying REST endpoint declarations, GraphQL schemas and API framework usage.
2. Perform API gateway and management platform analysis
API gateways serve as centralized chokepoints for API traffic, making them valuable sources of truth for discovering active APIs in an organization. Gateways such as Apigee maintain comprehensive registries of deployed APIs, including metadata about endpoints, versions, traffic patterns and usage analytics.
Gateway-based API discovery offers the following advantages:
- Complete API inventory from centralized registration processes.
- Traffic analytics showing actual API usage and consumption patterns.
- Version tracking across different API iterations and deployments.
- Performance metrics that indicate which APIs are actively used versus dormant.
Gateway inventories have limitations, however. Not all APIs route through gateways — for example, internal microservice communications, legacy endpoints and development APIs often bypass this infrastructure entirely. Use gateway data as a primary inventory baseline, but supplement with other discovery methods to capture the complete API landscape.
3. Audit third-party integrations
Modern applications depend heavily on external services, requiring systematic audits to understand the full scope of API dependencies. Review all SaaS integrations and vendor APIs that applications consume, examining authentication methods, data-sharing agreements and access permissions granted to external services.
Document all outbound API calls that applications make, including the types of data exchanged and the business purpose of each integration. This audit process often reveals unexpected data sharing relationships or insecure integration patterns not captured in official API documentation.
Pay particular attention to cloud service dependencies and their associated API endpoints, as these connections frequently bypass traditional network monitoring tools. Many organizations discover critical API dependencies only when external services experience outages or security incidents.
4. Implement continuous attack surface management
Deploy automated tools that continuously scan external-facing infrastructure for exposed APIs. Modern attack surface management tools use techniques such as directory enumeration, subdomain discovery and port scanning to identify endpoints that might have been deployed without proper security review.
Focus on common API paths (*/api/*, */rest/*, */v1/*), HTTP methods and response patterns that indicate API interfaces. Advanced tools can differentiate between static web content and dynamic API endpoints, helping identify APIs not captured through other discovery methods.
5. Use network traffic analysis and SIEM integration
SIEM platforms excel at ingesting and analyzing network traffic data to reveal API usage patterns, even though they don’t provide native API discovery capabilities. These platforms process network flow logs, HTTP traffic data and communication patterns to identify potential API endpoints across your infrastructure.
Configure SIEM platforms to do the following:
- Analyze HTTP traffic logs for API endpoint patterns and REST-like URL structures.
- Monitor DNS queries to API domains (api., rest., *.amazonaws.com, *.googleapis.com).
- Track port usage and protocol analysis for nonstandard API communications.
- Correlate traffic patterns with application deployment timelines to identify new APIs.
Microsoft Sentinel demonstrates this approach well, integrating with Azure Network Watcher traffic analytics to process network security group flow logs and identify HTTP/HTTPS traffic patterns and connection dependencies.
Other major SIEM platforms — Splunk, IBM QRadar and Elastic Security — offer similar network analysis capabilities, enabling security teams to build custom correlation rules that flag API-like traffic patterns and suspicious communication behaviors.
6. Configure EDR tools for runtime discovery
Endpoint detection and response (EDR) tools provide powerful runtime insights into API activity through comprehensive endpoint monitoring. For example, CrowdStrike Falcon offers real-time visibility into endpoint activities while tracking network connections, DNS requests and process-level communication patterns.
EDR API discovery capabilities include the following:
- Process monitoring. Track applications making API calls by analyzing process execution and command-line arguments.
- Network analysis. Monitor HTTP/HTTPS connections, DNS queries to API domains and unusual port usage.
- Behavioral detection. Identify patterns indicating unauthorized API usage or API abuse.
- Real-time discovery. Detect new API communications as they occur across the organization.
EDR tools excel at identifying APIs that only activate under specific conditions or during business processes, making them essential for discovering conditional or time-based API usage that static analysis might miss.
7. Conduct continuous monitoring and integration
API discovery isn’t a one-time activity — it requires ongoing integration across multiple discovery methods.
Establish automated processes that combine the following:
- Source code scanning integrated into continuous integration/continuous delivery pipelines.
- API gateway analytics with automated inventory updates.
- Network traffic analysis through SIEM platforms.
- EDR monitoring for runtime API discovery.
- Regular third-party integration reviews.
Create dashboards that consolidate findings from all discovery methods, identify gaps between different inventories and flag newly discovered APIs for security assessment. This multilayered approach ensures comprehensive visibility as an organization’s API landscape evolves.
By implementing these discovery practices across the entire SDLC, security teams can maintain thorough API visibility and ensure adequate protection for these critical integration points.
How to implement API discovery best practices
Implementing these best practices as an integrated security program rather than as isolated activities is key to successful API discovery.
Start with source code analysis to establish the organization’s baseline API inventory, then layer on gateway monitoring, network traffic analysis and runtime EDR to capture the full spectrum of API use across the network.
Remember that APIs are dynamic — new endpoints emerge through development cycles, legacy APIs get deprecated and shadow APIs appear when teams bypass official processes.
Colin Domoney is a software security consultant who evangelizes DevSecOps and helps developers secure their software. He previously worked for Veracode and 42Crunch and authored a book on API security. He is currently a CTO and co-founder, and an independent security consultant.
