What is API Discovery? Everything You Need to Know

Only 30% of AppSec teams are confident they have visibility into their entire application attack surface. This lack of visibility creates real business risk. 

One of the biggest API breaches reported on last year was due to a deprecated endpoint that threat actors exploited to validate stolen payment card data before exfiltration. Because the legacy API remained undocumented in security inventories, traditional monitoring tools missed the malicious traffic entirely. The campaign ran undetected for months, showing how forgotten APIs become prime targets for attackers.

This is the API discovery problem. As applications grow more complex with microservices architectures and distributed systems—and AI coding assistants exponentially increase the amount of code being shipped—APIs multiply faster than documentation can keep up. Without comprehensive visibility, organizations face real, exploitable security gaps.

In this guide, we’ll cover:

• What API discovery is and why it matters for modern dev teams
• The difference between traffic-based and code-based discovery approaches
• How to identify and secure shadow, zombie, and rogue APIs
• Compliance requirements driving API discovery adoption
• Common mistakes that undermine discovery efforts
• How to implement continuous API discovery across your development lifecycle

What Does API Discovery Mean?

API discovery is the process of identifying every single API endpoint in your organization, whether active or forgotten. This includes understanding the full scope of interactions possible within and across systems. As APIs are discovered, they include those developed internally, those provided by third-party providers, and most crucially, APIs that may be hidden or unknown.

Think of API discovery as creating an up-to-date inventory of all the APIs, or more broadly, digital “connection points” within your systems. The API discovery process involves uncovering details such as:

• Endpoints: The URLs that applications use to interact with the API.
• Methods: The supported actions (GET, POST, PUT, DELETE, etc.).
• Parameters: The data an API can accept and the responses it generates.
• Authentication/Authorization: How the API ensures only permitted users or applications can access it.
• Protocol and architecture: Whether the API uses REST, GraphQL, gRPC, or SOAP.

Data sensitivity: Which APIs handle PII, PCI, PHI, or other regulated data.

Why Does API Discovery Matter?

API discovery delivers tangible benefits that directly impact your security posture and operational efficiency. Whether you’re managing a handful of APIs or thousands, API discovery should be part of your security and development toolkit.

Identifies Security Vulnerabilities Before Attackers Do

Having a complete API inventory allows organizations to understand which APIs are in use and which are not. Security teams can’t patch vulnerabilities in APIs they don’t know about. These forgotten endpoints—such as shadow APIs and zombie APIs—expand your API attack surface.

Accelerates Compliance Documentation

API discovery helps organizations meet regulatory requirements by documenting data flows and access controls. Automated discovery generates the documentation auditors need, reducing manual effort and audit preparation time.

This matters for:

• PCI DSS v4.0.1: Organizations must maintain an inventory of all bespoke and custom software
• GDPR Article 30: Requires documentation of all data processing activities, including APIs handling personal data
• EU Cyber Resilience Act: Mandates complete SBOM including API dependencies
• ISO 27001: Requires asset inventory including all information processing systems

​​Reduces Development Costs and Time-to-Market

Discovery reveals existing APIs that solve the problem you’re tackling, saving development time and resources by eliminating duplicate work. When developers can quickly find what already exists, they build faster instead of recreating functionality buried in another service. Automated discovery tools plus a centralized API catalog streamlines identification and documentation, allowing developers to focus on building new features instead of manually tracking down endpoints.

The Hidden API Problem: Shadow, Zombie, and Rogue APIs

Hidden APIs are those that exist within a system but are not cataloged or included in the official documentation. Such APIs become a significant security and management concern since they slip through the cracks of security testing and patching.

Shadow APIs

These are unintentionally exposed APIs, often created by developers during testing or for temporary purposes. Shadow APIs might not follow established security standards or documentation practices, leading to potential vulnerabilities being exploited by attackers.

Shadow APIs arise from all sorts of errors and sloppiness in security policy. Developers might simply forget to document them. Sometimes older APIs are removed from documentation although they still exist. Company mergers are notorious for producing lots of shadow APIs. Developers create shadow APIs for testing purposes or very small bespoke use cases and don’t bother to alert security teams to their presence.

Zombie APIs

These refer to obsolete or deprecated APIs that are meant to be decommissioned but remain active within a system. Poor versioning practices and inadequate tracking of decommissioning processes result in these APIs continuing to exist among the mix of available APIs, representing potential security risks if they’re not properly patched or removed.

Zombie APIs may have been properly secured and maintained at some point but have since been left to languish, perhaps unknown even to the application owner who created them. Zombie APIs are typically not updated or patched but still provide a hidden door to some part of the application’s system.

Rogue APIs

These APIs are deliberately created and hidden, often with malicious intent. As a backdoor into the system via API, a rogue API may be designed to circumvent security controls or exfiltrate data without authorization. Some organizations use “shadow API” and “rogue API” interchangeably, while others use “rogue API” to refer to APIs that are deliberately malicious.

Some of the key risks hidden APIs introduce:

• Unpatched Vulnerabilities: Hidden APIs contain undetected and unpatched vulnerabilities, especially zombie APIs that are no longer actively maintained. This makes them easy targets for attackers.
• Expanded Attack Surface: Hidden APIs increase the available attack vectors for malicious actors to exploit. Attackers discover these APIs through trial and error, code leaks, or automated scanning.
• Data Exposure: Poorly secured or undocumented APIs serve as gateways for unauthorized data access or leaks. Attackers use hidden APIs to retrieve sensitive data or manipulate the system unnoticed.
• Compliance Violations: Hidden APIs lead to non-compliance with data privacy regulations such as GDPR or industry-specific standards. Ensuring proper authorization and access controls on undocumented APIs becomes difficult due to minimal oversight.

Proactive discovery of hidden APIs is crucial. By keeping track of every single API within your organization’s API portfolio, you enhance your capabilities for mitigating these risks and maintaining a strong security posture.

What Makes an API Discoverable?

Discovering APIs involves many potential processes, which will be discussed in the next section. However, it’s important to first consider some factors that make an API discoverable. Here are key facets that contribute to the discoverability of APIs.

Clear and Comprehensive Documentation

Well-written documentation is the cornerstone of API discoverability. It should provide a thorough overview of the API’s purpose, how to use it, the different methods it supports, the parameters it accepts, expected responses, potential error codes, and illustrative examples.

Think of this documentation as a user-friendly guidebook for your API. This includes following well-known documentation practices, such as creating OpenAPI specifications for your APIs.

Developer Portals

Exposing APIs through a developer portal makes them easily discoverable. A developer portal is like a central marketplace for your APIs. It lists available APIs, provides powerful search functionality, and often includes features that allow for interactive testing of the APIs, such as Swagger UI. This enables developers to find the APIs they need quickly and experiment with them easily.

Descriptive and Standardized Naming Conventions

Consistent naming conventions for endpoints and parameters significantly aid discoverability. Naming and parameters should be predictable and allow developers to understand your API’s structure easily. Using meaningful names helps developers infer the functionality of an API even before they have read the complete documentation.

Adherence to Design Standards

Using widely recognized standards such as REST or GraphQL makes your API more intuitive for developers. These standards establish familiar patterns and conventions, which lessen the learning curve for developers who are integrating with and utilizing your API, thus enhancing its discoverability.

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These points reflect more of a manual approach to API discovery. In these cases, following the above guidelines allows developers, internal or external, to quickly see what APIs are available and enables them to use the APIs effectively. But what about discovering hidden APIs? Automation is your friend.

Manual vs. Automated API Discovery

There are two primary ways to approach API discovery. Both have particular use cases and methods associated with them.

Manual Methods

Manual methods are likely familiar to developers who use APIs. Many of these methods require a technical background and focus on discovering APIs before using them or figuring out which ones are currently used within a codebase. Here are a few ways developers can manually discover available or in-use APIs.

• Code Review: Carefully scrutinizing source code to identify how APIs are defined and used.
• Network Traffic Analysis: Inspecting network packets to trace communication patterns between applications, revealing API usage. Monitoring API traffic helps identify API usage and detect anomalies.
• Referencing Existing Documentation: Reviewing any available API documentation, system architecture diagrams, or developer notes.

These manual techniques prove useful in certain scenarios, but they have limitations. They are labor-intensive and time-consuming, and they miss hidden APIs that don’t leave obvious traces in the code or network traffic. When you’re managing hundreds or thousands of endpoints, manual discovery becomes impractical.

Automated Methods

Specialized API discovery tools are needed for automated methods of API discovery. These can involve tools built into API management platforms, API security platforms, and other tools that support discoverability. These tools are built to scan systems, analyze network patterns, and even probe endpoints to actively uncover APIs. They provide a comprehensive, scalable, and efficient way to identify documented and hidden APIs.

Automated API discovery tools utilize API traffic data to identify calls within the network, contributing to effective management and oversight of API interactions. Other solutions, such as StackHawk, scan through code repositories to find potential endpoints written within the code and catch APIs before they reach production.

API Discovery Approaches: Understanding Your Options

Different discovery approaches find different types of APIs. Understanding these methods helps you choose the right combination for your organization.

Traffic-Based Discovery

How it works: Monitors network traffic and API gateway logs to identify endpoints based on actual usage.

What it finds: Active APIs receiving production traffic, usage patterns, and frequently-called endpoints.

What it misses: Pre-production APIs, rarely-called endpoints, APIs not yet deployed, internal microservices bypassing gateways.

Best for: Understanding current API usage patterns and identifying high-traffic security priorities.

Tools: API gateways (Kong, Apigee), CDN providers (Cloudflare, Akamai), network monitoring platforms.

Code Repository Discovery

How it works: Scans source code repositories to identify API endpoint definitions regardless of whether they’re deployed or receiving traffic.

What it finds: All defined endpoints including staging, development, and pre-production APIs. Catches endpoints before they’re deployed.

What it misses: APIs not yet committed to version control, third-party APIs without local definitions.

Best for: Shift-left security practices, catching shadow APIs during development, preventing vulnerabilities before production.

Tools: StackHawk (code-based discovery + DAST testing), static analysis tools with API detection.

Hybrid Approach: The Most Complete Coverage

Organizations with mature API security practices use both methods:

1. Code-based discovery finds APIs early in the development lifecycle
2. Runtime traffic monitoring validates what’s actually being used in production
3. Together they provide complete visibility across the entire API lifecycle

Types of API Discovery Platforms and Tools

Quite a few API discovery tools are available to fully leverage automated API discovery. Most of them are within API management and security platforms.

• API Management Platforms and Gateways: Gateways, such as Kong or Apigee, often include API discovery capabilities because they control traffic and offer insights into API usage. These platforms excel at discovering APIs flowing through their infrastructure but may miss endpoints that bypass the gateway.
• Security Scanners: Specialized tools such as StackHawk proactively scan for vulnerabilities and map your API endpoints, exposing previously unknown ones. StackHawk’s unique approach combines code repository scanning with runtime testing to find APIs before they reach production and validate their security through automated DAST scans.
• Cloud Provider Tools: AWS, Azure, and GCP offer API discovery within their ecosystems, typically through API Gateway services and CloudTrail/logging mechanisms.

Automated API discovery tools often offer organizations a significant advantage in maintaining a complete and up-to-date understanding of their API inventory and improving their API security posture.

5 API Discovery Mistakes That Create More Problems

Avoid these common pitfalls when implementing API discovery:

1. Discovering but not prioritizing

Creating a catalog of 1,000 endpoints helps no one if they’re not prioritized by risk. Focus first on APIs handling sensitive data (PII, PCI, PHI), public-facing endpoints, and authentication mechanisms.

2. Only discovering REST, ignoring GraphQL/gRPC/SOAP

Many organizations focus exclusively on REST APIs while GraphQL and gRPC usage explodes. Comprehensive discovery covers all protocol types in your environment.

3. Finding shadow APIs but not assigning ownership

Discovery without accountability creates “someone else’s problem” APIs. Every discovered endpoint needs a responsible team assigned for maintenance and security.

4. Treating discovery as a security-only initiative

Discovery succeeds when developers and security collaborate. Security teams identify risks; developers understand context and can validate whether endpoints are still needed.

5. Discovering once instead of continuously

APIs change constantly. New endpoints ship daily in fast-moving organizations. One-time discovery creates a snapshot that’s outdated within weeks. Continuous discovery keeps your inventory current.

Using StackHawk For API Discovery

StackHawk’s API discovery feature enables developers to bundle together a modern DAST platform with the capabilities for continuous API discovery. This innovative tool empowers users to discover API endpoints, including rogue and shadow APIs, and bolster the detection of vulnerabilities throughout your entire API inventory.

What Makes StackHawk’s Approach Different

Code-first discovery: StackHawk scans source code repositories to find API endpoints before they reach production. This shift-left approach catches shadow APIs during development, when they’re easiest to document or remove.

Multi-protocol support: Unlike tools that focus exclusively on REST, StackHawk discovers REST, GraphQL, gRPC, and SOAP endpoints. Your attack surface isn’t limited to one protocol, and your discovery shouldn’t be either.

Discovery + security testing: Finding endpoints is just the first step. StackHawk immediately tests discovered APIs for OWASP API Security Top 10 vulnerabilities, so you’re not just cataloging—you’re securing.

CI/CD integration: Discovery happens automatically during your existing development workflow. New endpoints are found and tested before they merge to main, not weeks later during a security audit.

Minute-long scans: Fast feedback loops mean developers get security results while context is fresh. StackHawk’s optimized scanning completes in minutes, not hours.

By allowing users to discover API endpoints previously unknown, such as rogue and shadow APIs, StackHawk’s API discovery tool augments the uncovering of API vulnerabilities across your entire API inventory.

Don’t wait for the next breach to discover what’s exposed. StackHawk helps organizations mitigate the security risks outlined in the OWASP API Top Ten and beyond to find and fix vulnerabilities before attackers do.

Schedule a demo or start your free trial today to discover hidden APIs and test them for vulnerabilities in minutes, not weeks.