As companies adopt API‑first design practices to build modern applications, measuring the operational performance and value of those APIs becomes a top priority. Establishing a framework that clearly defines and connects API metrics with key performance indicators (KPIs) is one of the most important steps to ensure a successful API strategy.
Typically, KPIs are tied to specific goals. They have a defined time frame and are aligned to the outcomes that your API strategy needs to deliver. API metrics, in contrast, are significant data points. Not every metric is a KPI, but every KPI begins as a metric.
So, how do you start? First, you need to be clear – at the outset – about the goal of your API strategy and then choose the metrics that align with that goal. Remember that each team needs to measure and track different metrics depending on what is important to it and what is essential for the business.
Broadly, there are three overarching types of API metrics that companies can track, and each type answers a different question:
- Operational metrics – Are APIs delivering the stability, reliability, and performance you need?
- Adoption metrics – Are developers adopting and using your APIs?
- Product metrics – How are APIs supporting your business objectives?
Imagine these overarching metrics as a pyramid. At the bottom, operational metrics measure the tactical performance of individual APIs and the infrastructure supporting them. At the top, product metrics measure the business value created by your APIs. The two are connected by adoption metrics, which track the growth of the API program with end users (developers). Generally, product metrics and adoption metrics align to the business outcomes you need to measure, while operational metrics align with the technical standards you need to maintain.
In this post we break down 12 specific metrics that are critical to measure, discuss how they enable infrastructure and application teams, and explain the ways the metrics relate to KPIs.
When you are just getting started, operational metrics are usually the first thing to measure. They are tactical and provide insights into how APIs are functioning. Operational metrics are not usually KPIs themselves. Instead, they help you measure the quality and performance of the software your teams are building. They can provide early indicators of emerging problems, or help you drill down and discover issues that might be impacting your critical KPIs.
The operational metrics you track will vary by team and responsibility.
Platform Ops is the team responsible for maintaining, connecting, and securing the collection of infrastructure and technologies used by different teams to deliver applications. For API programs, this often includes API gateways and API developer portals.
Key metrics for infrastructure teams like Platform Ops include:
- Uptime – Even as one of the most basic metrics, uptime is the gold standard for measuring the availability of a service. This is often tied to a service level agreement (SLA).
- CPU and memory usage – Tracking resource utilization at the API gateway is critical to identifying when you might need to scale out your instances. It also acts as an early warning when something is starting to break or usage is spiking due to errors.
- Total pass and error rates – Measuring how often APIs trigger HTTP error (non‑
200) status codes helps you understand how error‑prone your APIs may be. This aggregate measure provides information to help judge the overall quality of the APIs your teams are putting into production.
Application teams, made up of API developers and service owners, are responsible for building and operating individual services or applications. These could be used as part of a larger product, to integrate with a partner, or when delivering APIs as a service to developers.
The following metrics are important for application teams to measure:
- Requests per minute – This performance metric measures the number of requests your API is handling. While it varies over time, you typically want to downwardly manage it to ensure the best experience for API users.
- Average and maximum latency – Tracking the average time it takes your API to receive a request and return a response is crucial. A single slow API can negatively impact the user experience and therefore negatively impact the business.
- Errors per minute – Like everything else, no API is perfect. Failures are a matter of when, not if. You need to monitor errors and have in place a planned course of action for fixing them before they suddenly start to tick up.
Dig into API operations and learn which KPIs and metrics are critical from a business perspective in chapters 3–5 of the eBook Mastering API Architecture from O’Reilly, compliments of NGINX.
For an API‑first business, it’s essential to look beyond engineering metrics and understand how developers are interacting with your APIs. You also need to measure and monitor the API developer experience to ensure developers are adopting and getting value from your APIs.
A few examples of adoption metrics include:
- Unique API consumers – Often time‑bound into monthly users, this metric measures how many developers are adopting and using your APIs. Ideally this metric grows over time as more developers integrate your API into their applications.
- API usage growth – This metric also measures API adoption and is often the preferred metric for doing so. Ideally, API traffic grows monthly as the number of applications and developers using them also increases.
- Time to first call – This metric measures how long it takes a developer to create an account, generate API credentials, and run the first API call. Enabling developers to get up and running as fast as possible is a high priority, making this metric the most important for measuring the overall API developer experience.
Note: We recommend that at least one of your KPIs seeks to measure API adoption. This helps calculate the overall growth of your API program. For example, you might set a KPI to increase the number of developers who have created an ongoing integration or app using your API.
API product metrics play a major role in understanding the value of an API. Although only a small subset of APIs may directly contribute to revenue, every API needs to provide value to the business.
Key product metrics to measure include:
- Direct and indirect revenue – These metrics target the different ways APIs contribute to revenue. While some APIs are directly monetized, others support integrations with business partners or are third‑party integrations valued by customers. As with the adoption rate for your APIs, tracking indirect revenue helps developers build revenue‑generating apps for partners.
- Applications per API – APIs need to be reusable. This metric measures how many applications integrate with an API to see which APIs provide the most value.
- Number of partners – APIs often enable business relationships. Tracking the number of partner API integrations helps drive adoption and demonstrate value to other business units.
Note: These product metrics align closely with business impact, and you might choose to turn some into KPIs depending on your business goals. For example, if the business goal of your API strategy is to reach more customers through third‑party providers, you want to track both the number of partners using your APIs and the indirect revenue generated through those integrations.
Explore the API product lifecycle – including business and operational KPIs – in more depth in chapters 3–5 of Mastering API Architecture.
Aligning API metrics and business KPIs is one of the principal ways to make data‑driven decisions and ensure your API strategy delivers the value your organization requires. And not only that – gaining visibility into your APIs can also empower infrastructure and application teams to measure the operational metrics that matter most to them.
At NGINX, we provide visibility into dozens of important API metrics. You can view real‑time and historical metrics, and easily export them to your preferred application performance monitoring (APM) or data analytics solution.
Get started today with a 30‑day free trial of NGINX Management Suite, which includes access to API Connectivity Manager, NGINX Plus as an API gateway, and NGINX App Protect to secure your APIs.