API Penetration Testing: Scope, Methodology & Cost 2026

APIs are where modern applications actually live and where most of the significant security vulnerabilities are found. A web application pentest that doesn't explicitly include your API surface isn't testing the majority of your attack surface. It's testing the interface in front of it.

This guide is written for the people making the security buying decision. If you've been using our JWT Analyzer or API Key Checker and discovered issues you want properly assessed, or if you're preparing for a SOC 2 or security audit and need to understand what API pentesting involves this covers what you need to know before engaging a provider.

1. What API Penetration Testing Is
2. Who Needs a Dedicated API Pentest
3. What the Methodology Should Cover
4. Authentication Testing: JWT, OAuth, API Keys
5. The OWASP API Security Top 10 — What It Means for Scope
6. What a Real API Pentest Report Contains
7. API Penetration Testing Cost in 2026
8. Get an API Pentest Quote

What API Penetration Testing Is

API penetration testing is a manual security assessment of your application's API layer the endpoints, authentication mechanisms, data handling, and business logic that power your product's backend. It's conducted by a human tester who probes your API the way an attacker would: systematically, creatively, and with the goal of finding what automated scanners and internal teams miss.

The distinction from a standard web app pentest matters practically. Web app pentests typically evaluate what a browser-based user can do. APIs expose a broader and often less-governed surface: endpoints without UI-level access controls, business logic that developers assumed would only be called correctly, authentication flows that behave differently when called directly, and data that's returned without the filtering a frontend would apply.

In most modern applications SaaS products, mobile apps, microservices architectures, third-party integrations the API surface is larger and more dangerous than the web interface sitting in front of it.

What API pentesting is not: Running an OpenAPI spec through an automated scanner and generating a report. That finds known vulnerability patterns in documented endpoints. It doesn't find the undocumented endpoints, the authorisation logic failures, the rate limiting gaps, the JWT weaknesses, or the data exposure issues that require a tester who understands your API's intended behaviour to identify.

Who Needs a Dedicated API Pentest

A dedicated API assessment is the right approach when:

Your product is API-first or mobile-first. If the primary interface to your application is an API whether consumed by a mobile app, a third-party integration, or other services the API is your entire attack surface. A web application pentest scoped to a browser interface doesn't cover it.

Your web app pentest didn't explicitly include API testing. Many web app pentest scopes cover what a browser-based user can do and leave API endpoints implicitly in scope but undertested. Ask your provider explicitly: were individual API endpoints tested for broken object level authorisation? Was authentication bypass attempted directly against API endpoints? If the answer is unclear, your API wasn't properly tested.

You've found issues with your own tooling. If you've run our JWT Analyzer and flagged weak secrets, missing claim validation, or insecure algorithm configuration or used the API Key Checker to identify exposed credentials those are signals that a manual assessment will find more. Tools surface individual issues; a pentest maps the full attack surface and chains findings into realistic attack paths.

You're preparing for SOC 2, ISO 27001, or a security review. Compliance auditors increasingly ask specifically about API security testing. A pentest that doesn't address the API layer is incomplete evidence. If your product's primary data exposure risk sits in the API, your compliance testing should too.

You have a microservices architecture. Service-to-service authentication, internal API trust assumptions, and lateral movement through service mesh are all testable attack surfaces that only a dedicated API assessment covers.

What the Methodology Should Cover

A comprehensive API pentest covers several distinct phases. When evaluating providers, ask specifically what's included at each stage the gaps between providers are almost always in what they leave out.

Endpoint discovery and attack surface mapping. Before testing anything, the tester needs a complete picture of what's testable: all endpoints (documented and undocumented), HTTP methods accepted, parameters, authentication requirements, and data returned. This includes discovering endpoints not in the documentationlegacy routes, debug endpoints, version inconsistencies because undocumented endpoints are disproportionately vulnerable.

Authentication and authorisation testing. How does the API verify who a caller is, and whether they're allowed to do what they're requesting? This is the highest-yield area of most API assessments. Testing covers: JWT validation and all associated weakness classes, OAuth flow security, API key handling and rotation, session management, and privilege escalation between user roles. See the dedicated JWT and authentication section below.

Object-level authorisation (BOLA/IDOR). Can an authenticated user access or modify objects belonging to another user by changing an identifier in the request? This is the number one API vulnerability category globally and almost entirely a manual testing problem. Automated tools don't find BOLA reliably because it requires the tester to understand what objects exist, which users own them, and what the correct access boundary should be.

Function-level authorisation. Can a regular user call endpoints intended for administrators, or perform actions outside their permitted role? These failures are often invisible in the frontend a non-admin user simply doesn't see the button but accessible directly via API.

Mass assignment and excessive data exposure. Does the API accept and process properties it shouldn't allowing users to set fields like isAdmin or accountBalance that should be server-controlled? Does it return data that should be filtered full objects when only specific fields were requested? Both are common and consistently underdetected by automated testing.

Rate limiting and resource consumption. Are endpoints protected against brute force, credential stuffing, and resource exhaustion? Authentication endpoints without rate limiting are a credential spray target. Computationally expensive endpoints without limits are a denial-of-service vector.

Business logic testing. API-specific logic flaws multi-step flows that can be completed out of order, quantity or value fields that aren't server-validated, state transitions that shouldn't be accessible from certain starting states. These require understanding the application's intended behaviour and are entirely a manual testing activity.

Third-party and integration security. APIs that call or receive calls from third-party services, webhooks, or partner integrations create additional trust boundaries. Are incoming webhook payloads validated? Are outbound calls to third parties authenticated and scoped correctly?

Authentication Testing: JWT, OAuth, API Keys

Authentication is the most consequential area of API security testing weaknesses here typically mean full account access or complete authentication bypass. Here's what each major API authentication mechanism should be tested for:

JSON Web Tokens (JWTs)

JWTs are the dominant authentication mechanism for modern APIs, and they have a well-documented attack surface. Manual testing covers: algorithm confusion attacks (accepting HS256 when RS256 is expected, or accepting alg: none), weak HMAC secret bruteforcing, missing or improper claim validation (no exp check, no aud validation, no iss verification), token replay after logout, and key confusion attacks.

If you've used SecurityWall's JWT Analyzer on your own tokens, you've already assessed the static properties of individual tokens. A pentest goes further it tests how the server responds to manipulated, expired, and malformed tokens in context, across all endpoints that accept them.

OAuth 2.0 flows

OAuth is frequently misconfigured in ways that have significant security consequences: open redirect vulnerabilities in authorization endpoints, insecure state parameter implementation (CSRF in OAuth), authorisation code interception, improper scope validation, and token leakage through referrer headers. Each flow type authorisation code, PKCE, implicit, client credentials has distinct vulnerabilities.

API keys

API key testing covers how keys are issued, transmitted, stored, scoped, and rotated. Specifically: whether keys are transmitted in URLs (logged by proxies and servers), whether key entropy is sufficient, whether keys are scoped to the minimum necessary permissions, whether there's a key rotation and revocation mechanism, and whether leaked keys can be identified using tools like our API Key Checker to understand blast radius.

Service-to-service authentication

Internal APIs that trust service identity rather than user identity typically using static API keys, mutual TLS, or service mesh tokens have their own weaknesses. Testing evaluates whether a compromised service account or token can be used to pivot to other internal services, and whether service permissions are properly scoped.

The OWASP API Security Top 10 — What It Means for Scope

OWASP maintains a dedicated API Security Top 10 separate from the web application Top 10 that maps the vulnerability categories most commonly exploited in production APIs.

What a Real API Pentest Report Contains

The report is what you're paying for. Before selecting a provider, ask for a redacted sample. Here's what distinguishes a genuine API pentest report from an automated scan output:

Endpoint coverage documentation. A list of all endpoints tested — including those discovered during the engagement that weren't in the original scope definition. This tells you what was actually assessed, and creates a baseline for future testing.

BOLA and authorisation findings with evidence. A real BOLA finding includes: the specific endpoint, the parameter manipulated, the account or object accessed without authorisation, a screenshot or response body showing the unauthorised data, and step-by-step reproduction instructions. An automated scan cannot produce this. If a report has no BOLA findings and BOLA is the #1 API risk, either the API is unusually well-built, or it wasn't tested.

Authentication findings with exploitation evidence. JWT findings should include the specific weakness (algorithm confusion, weak secret, missing claim), the token manipulation performed, and evidence of the server's response to the manipulated token. OAuth findings should include the specific flow step where the vulnerability exists.

CVSS-scored findings with business impact context. Each finding rated by severity, with an explanation of what an attacker could actually do with it not just the technical description of the vulnerability.

Remediation guidance at the implementation level. Not "fix the BOLA" specific guidance on what the authorisation check should look like, at which layer it should be enforced, and how to validate the fix. Your engineering team acts directly on this.

Retest evidence. After remediation, the provider should retest critical and high findings and document the resolution. For SOC 2 and other compliance purposes, retest evidence is what auditors verify not just the initial findings list.

For compliance-specific requirements on what pentest documentation needs to contain, see our SOC 2 penetration testing requirements guide.

API Penetration Testing Cost in 2026

API pentest pricing depends on the number of endpoints, authentication complexity, and how many distinct user roles and object types need to be tested for authorisation coverage.

GraphQL APIs carry a separate line because they have distinct vulnerabilities introspection abuse, query batching for rate limit bypass, field-level authorisation failures, and deeply nested query DoS that require different testing techniques from REST. If your API is GraphQL, confirm explicitly that your provider has GraphQL-specific testing experience, not just REST methodology applied to a GraphQL endpoint.

API security is where the most significant vulnerabilities in modern applications live and where the gap between "we had a pentest" and "we had a pentest that covered the API properly" is widest. BOLA, authentication weaknesses, function-level authorisation failures, and business logic flaws are the findings that matter most and the ones that automated testing misses most consistently.

If you've already used the JWT Analyzer or API Key Checker and flagged issues, those are specific, evidenced problems that a manual assessment will contextualise, extend, and chain into a realistic picture of your actual exposure. Individual tool findings tell you something is wrong. A pentest tells you the full scope of what an attacker could do with it.

Get an API Pentest Quote

Related reading:

• Penetration Testing Services
• JWT Analyzer — Free Tool
• API Key Checker — Free Tool
• Web Application Penetration Testing Guide
• SOC 2 Penetration Testing Requirements
• PTaaS: The Complete Buyer's Guide

API Penetration Testing, API Security Testing, OWASP API Top 10, BOLA, Broken Object Level Authorisation, JWT Security, REST API Testing, GraphQL Security Testing, OAuth Security, API Key Security