API Inventory

Definition

An API Inventory is a centralized, machine-readable catalog of all APIs in an organization, containing essential metadata about each endpoint: who owns it, what it does, how to access it, and its current lifecycle stage. Think of it as the “source of truth” that answers “What APIs do we have?”

Unlike static documentation (Swagger files, README docs), an API Inventory is a living database that reflects current reality. It’s continuously updated through automated API Discovery, manual registration, and lifecycle management processes. The inventory enables governance, security monitoring, and architectural planning by providing a complete view of an organization’s API landscape.

A mature API Inventory captures not just “this endpoint exists,” but critical context: authentication requirements, data classification (does it process PII?), dependencies (what services does it call?), SLAs, deprecation status, and ownership (who fixes it when it breaks?).

Example

Before Inventory (Chaos):

Developer: “Is there an API to get customer orders?”
Response: “Maybe? Check Slack, ask the Platform team, or search Confluence?”
Result: Developer builds a duplicate API because they can’t find existing one

After Inventory (Clarity):

Developer searches inventory: “customer orders”
Finds: GET /api/v2/orders - Owner: Alice, Status: Active, Auth: OAuth2
Result: Reuses existing API, contacts owner for access

Real-World Example - Stripe’s API Catalog:

{
  "endpoint": "/v1/customers",
  "method": "POST",
  "description": "Creates a new customer object",
  "owner": "[email protected]",
  "status": "active",
  "version": "2023-10-16",
  "authentication": "bearer_token",
  "rateLimit": "100 requests per second",
  "dataClassification": "PII",
  "dependencies": ["identity-service", "billing-service"],
  "documentation": "https://stripe.com/docs/api/customers/create",
  "openapi": "https://api.stripe.com/openapi/v1/customers.yaml"
}

Analogy

The Library Catalog: A library doesn’t just store books on shelves—it maintains a catalog system (Dewey Decimal, Library of Congress). You can search by title, author, subject, or ISBN. The catalog tells you if a book exists, where to find it, if it’s checked out, and when it’s due back. An API Inventory is this catalog for APIs—it’s not the APIs themselves, but the system that helps you find and understand them.

The Building Directory: In a large office building, the lobby directory lists every tenant: which floor they’re on, what they do, how to contact them. Without this directory, you’d wander floors randomly hoping to find the right office. An API Inventory is this directory for your API infrastructure.

Code Example

Inventory Schema (JSON):


{
  "api_inventory": {
    "total_apis": 247,
    "last_updated": "2026-01-14T10:30:00Z",
    "apis": [
      {
        "id": "api-customers-v2",
        "name": "Customer Management API",
        "base_url": "https://api.company.com/v2/customers",
        "version": "2.1.3",
        "status": "active",
        "lifecycle_stage": "production",

        "ownership": {
          "team": "customer-platform",
          "owner": "[email protected]",
          "oncall": "pagerduty://customer-platform"
        },

        "technical": {
          "authentication": ["oauth2", "api_key"],
          "protocols": ["https", "http2"],
          "rate_limit": "1000 req/min per client",
          "sla": {
            "uptime": "99.9%",
            "response_time_p95": "200ms"
          }
        },

        "security": {
          "data_classification": "confidential",
          "processes_pii": true,
          "compliance": ["GDPR", "SOC2", "HIPAA"],
          "last_security_review": "2025-12-01"
        },

        "dependencies": {
          "upstream": ["identity-service", "billing-service"],
          "downstream": ["mobile-app", "web-app", "partner-portal"]
        },

        "documentation": {
          "openapi_url": "https://api.company.com/openapi/customers-v2.yaml",
          "developer_docs": "https://docs.company.com/api/customers",
          "changelog": "https://docs.company.com/api/customers/changelog"
        },

        "metrics": {
          "requests_per_day": 2400000,
          "unique_clients": 347,
          "error_rate": "0.02%"
        }
      },
      {
        "id": "api-customers-v1",
        "name": "Customer Management API (Legacy)",
        "base_url": "https://api.company.com/v1/customers",
        "version": "1.9.2",
        "status": "deprecated",
        "lifecycle_stage": "sunset_planned",
        "sunset_date": "2026-06-30",
        "migration_guide": "https://docs.company.com/migration/v1-to-v2",

        "ownership": {
          "team": "customer-platform",
          "owner": "[email protected]",
          "note": "Maintenance mode only"
        },

        "metrics": {
          "requests_per_day": 150000,
          "unique_clients": 23
        }
      }
    ]
  }
}

Automated Inventory Updates:


// CI/CD Pipeline Integration
// Automatically register APIs during deployment

const inventoryClient = require('@company/api-inventory');

async function registerAPI() {
  // Extract metadata from OpenAPI spec
  const openapi = readFile('openapi.yaml');
  const metadata = parseOpenAPI(openapi);

  // Add deployment-time information
  const registration = {
    ...metadata,
    owner: process.env.TEAM_EMAIL,
    version: process.env.GIT_SHA,
    environment: process.env.DEPLOY_ENV,
    timestamp: new Date().toISOString()
  };

  // Register or update in inventory
  const result = await inventoryClient.register(registration);

  if (!result.success) {
    // Block deployment if registration fails
    throw new Error('API registration failed - deployment blocked');
  }

  console.log(`API registered: ${result.api_id}`);
}

// Run during deployment
registerAPI();

Diagram

graph TB
    A[API Inventory] --> B[Discovery Sources]
    B --> B1[API Gateway Logs]
    B --> B2[Code Repositories]
    B --> B3[Infrastructure Scans]
    B --> B4[Manual Registration]

    A --> C[Metadata]
    C --> C1[Ownership]
    C --> C2[Technical Details]
    C --> C3[Security Classification]
    C --> C4[Dependencies]

    A --> D[Consumers]
    D --> D1[Developers: Find APIs]
    D --> D2[Security: Audit Surface]
    D --> D3[Architects: Plan Changes]
    D --> D4[Compliance: Generate Reports]

    style A fill:#bbdefb
    style B fill:#c8e6c9
    style C fill:#fff9c4
    style D fill:#e1bee7

Required Metadata

Minimum Viable Inventory (must have):

Endpoint URL: Where is it?
Owner: Who’s responsible?
Status: Active, deprecated, sunset?
Authentication: How do clients authenticate?

Production-Ready Inventory (should have): 5. Description: What does it do? 6. Version: Which version is this? 7. Documentation link: Where to learn more? 8. Data classification: What sensitivity level?

Mature Inventory (comprehensive): 9. Dependencies: What does it call? What calls it? 10. SLAs: Uptime, latency guarantees 11. Rate limits: Throttling rules 12. Compliance: Regulatory requirements 13. Lifecycle stage: Development, production, deprecated 14. Metrics: Usage statistics, error rates

Common Mistakes

Mistake 1: Static Excel spreadsheet An Excel file updated quarterly is not an inventory—it’s outdated documentation. Inventories must be automated and real-time.

Mistake 2: Too much metadata required If registering an API requires filling 50 fields, developers will bypass the process. Start minimal, expand gradually.

Mistake 3: No enforcement If API registration is optional, your inventory will be incomplete. Integrate with CI/CD to enforce registration before deployment.

Mistake 4: Inventory without discovery Manual registration alone misses Shadow APIs. Combine manual registration with automated discovery to find undocumented endpoints.

Mistake 5: No ownership accountability “Platform team” as owner is meaningless. Every API needs a specific person with contact information.

Inventory vs Catalog

Aspect	Inventory	Catalog
Purpose	Governance & compliance	Developer experience
Audience	Security, architects, compliance	Developers, partners
Content	All APIs (even internal/undocumented)	Curated, published APIs
Metadata	Technical, security, compliance	Usage examples, tutorials
Automation	Discovery-driven	Documentation-driven

Relationship: Inventory is the complete list; Catalog is the public-facing subset. Think: Inventory = all books the library owns (including damaged/archived). Catalog = books available for checkout.

Best Practices

Automate discovery: Don’t rely on manual registration alone
Start minimal: Capture endpoint, owner, status. Add more metadata later
Enforce at CI/CD: Block deployments that don’t register
Single source of truth: One inventory tool, not multiple spreadsheets
Make it searchable: Developers should find APIs in seconds
Keep it current: Automated updates, not quarterly manual reviews
Link to docs: Inventory points to detailed documentation, doesn’t replace it

Tools for API Inventory

Open Source / DIY:

Backstage (Spotify): Developer portal with API catalog plugin
Custom database: PostgreSQL + API Discovery scripts
Git-based: YAML files in repository with CI validation

Enterprise Platforms:

Postman Private API Network: Team API catalog with collaboration features
Azure API Center: Microsoft’s centralized API inventory solution
SwaggerHub: API design platform with inventory capabilities
Apigee API Hub: Google Cloud’s API management and catalog

Specialized:

Akto: API Discovery + Inventory with security focus
42Crunch: API security platform with built-in inventory
Salt Security: Real-time API inventory from traffic analysis

Implementation Roadmap

Phase 1: Foundation (Month 1)

Choose inventory tool/platform
Define minimal metadata schema (5-7 required fields)
Manually register 20 most critical APIs
Create search interface for developers

Phase 2: Discovery Integration (Month 2-3)

Set up automated API Discovery (traffic + code + infrastructure)
Import discovered APIs into inventory
Assign owners to all discovered APIs
Reconcile: documented vs discovered

Phase 3: Automation (Month 4-6)

Integrate inventory registration into CI/CD pipeline
Block deployments without registration
Automated compliance checks (PII processing without GDPR tag = deployment blocked)
Dashboard showing inventory health metrics

Phase 4: Governance (Month 6+)

Quarterly reviews: remove decommissioned APIs
Ownership audits: reassign when employees leave
Security reviews: flag APIs without recent reviews
Analytics: most-used APIs, deprecation candidates

Assessment

Inventory Maturity Levels:

Level 0 - None: “We don’t know what APIs we have”

Level 1 - Static: Excel spreadsheet, manually updated

Level 2 - Semi-Automated: Database with manual registration + quarterly discovery audits

Level 3 - Automated: Real-time discovery, CI/CD integration, enforced registration

Level 4 - Governed: Automated + lifecycle management + compliance automation

Use the Shadow API Detection Tool to assess your current maturity level.