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To see API route latency in VS Code with API Performance Profiler, install its companion @api-profiler/express middleware in your Node.js app, put app.use(profiler()) before your routes, and generate some requests. The middleware observes the running app; the VS Code extension displays the resulting route figures and can present recorded requests for a load test.
What API Performance Profiler does
API Performance Profiler is a VS Code extension for viewing route timing information beside route definitions and in an API Profiler sidebar. Its documented focus is Express and NestJS projects using Express. The Visual Studio Marketplace listing describes the editor features; the companion @api-profiler/express package documentation describes the middleware that observes requests.
The extension is not described as measuring a running server on its own: the application needs the middleware to collect request data. The listing says it can identify Express route patterns and NestJS controller decorators, but that does not establish support for every project layout or dynamically constructed route.
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In your Node.js application, install the
@api-profiler/expresspackage using your project’s package manager. -
Import or require the package as shown in its documentation, then add
app.use(profiler())before route definitions. Middleware order matters: registering it after routes may prevent it from observing those requests. -
Start the application and send requests to its routes so the middleware has traffic to record.
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Install API Performance Profiler from the Visual Studio Marketplace, open the API Profiler view in VS Code, and inspect the available route figures. The listing also describes inline route decorations and a load-test action for routes with a recording.
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How to read the measurements
The package documentation describes route statistics over a rolling five-second window by default. Once there are enough samples, the available figures include request count, average latency, maximum latency, error rate, and requests per second. These are summaries of observed application traffic, not synthetic benchmark results.
The extension distinguishes observed traffic from generated load-test results. Its listing says, “A number that was not measured is never shown,” and notes that requests per second remain unavailable until enough samples exist. Treat an absent value as unavailable rather than as zero or a performance guarantee.
The Marketplace listing gives default display thresholds of 200 ms for fast and 500 ms for warning. These are extension display settings, not universal API targets or service-level objectives. The listing also specifies a default load-test configuration of 10 concurrent connections and five seconds; these describe the tool’s defaults, not a benchmark of your service.
Load-test safely
The package documentation describes replaying a recorded request against localhost. GET is enabled by default; other methods require explicit opt-in. This distinction matters because a replayed POST can write real data.
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Inspect the handler’s side effects before opting into non-GET requests. The replay includes an
x-api-profiler-load: 1header, which the package says handlers can use to skip actions such as sending mail or charging payments. Your application must implement and verify any such safeguards. -
Do not assume the header alone makes a request safe. Check every downstream effect and avoid pointing replay traffic at production systems.
Recordings, credentials, and production mode
A recorded request can contain live credentials. The package documentation says recordings stay in memory rather than being written to disk or sent elsewhere, and says credentials are masked in displays. It also says production mode disables recording and advises setting NODE_ENV=production on servers. These are vendor documentation claims, not an independent security audit; review what your requests contain and confirm the application’s environment settings.
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Compatibility, release, and licence
The npm listing extract available on October 9, 2026 reports @api-profiler/express version 0.1.0 and says it works with Express 4 and 5 and Node 18+. Package support and releases can change, so check the current npm package listing before installing or relying on those compatibility details. The Marketplace result identifies the extension licence as AGPL-3.0-only; review the listing and licence terms for your intended use.
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