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A VS Code extension can put a short latency label beside a relevant line of code using editor decorations. The hard part is not drawing the label: it is obtaining trustworthy timing data and reliably matching each measurement to the source that triggered the request. Choose and disclose that data path before promising general API coverage or “no cloud.”
What an inline latency extension can—and cannot—show
VS Code’s extension API supports editor decorations with before and after attachments, making a compact label beside a matched code range a plausible interface. For example, an extension could render “184 ms” after a line associated with a request. The number is useful only if the extension explains what it measures and how it linked the request to that line. See Microsoft’s VS Code API Reference.
Do not confuse decorations with debugger inline values. The API’s inline-values mechanism is for a debugger provider to display values at line ends when debugging stops; it is not a general live-latency display. Decorations are the more relevant presentation mechanism for this product concept.
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Choose where the timing data comes from
“API latency” can mean different things. A hover-triggered probe measures a request the extension itself makes. A runtime recorder measures requests made by the application. An OpenTelemetry receiver can display telemetry emitted by an instrumented application. These are different signals, with different coverage, setup requirements, and privacy implications; they should not be presented as interchangeable measurements.
#1 Best Overall
| Approach | What the timing represents | Coverage and trade-offs |
|---|---|---|
| Active endpoint probe | The response time of a new request initiated by the extension, not necessarily the application’s earlier request. | A Visual Studio Marketplace listing for API Hover Inspector describes sending a live HTTP request when a developer hovers over an API endpoint URL, then showing status, latency, headers, payload, and history. It also describes reading .env values and supporting request methods and bodies. These are publisher claims, not independent test results. A probe may need credentials and may have side effects, so make its method and trigger explicit. Marketplace listing |
| Runtime traffic recording | Timing observed from requests made by the running application, subject to what the recorder intercepts. | The Fetch Inspector Marketplace listing describes attaching a recorder to a Node development command, writing outbound fetch traffic to local NDJSON, and displaying calls in a panel. It says direct http.request calls—including axios’s default Node adapter—bypass its fetch recorder. That is a limitation of the described fetch-only approach, not a universal limitation of extensions. The listing also claims no uploads and no extension-originated network requests, and describes masking sensitive headers and body fields by default. Marketplace listing |
| Instrumented telemetry | Spans, logs, or metrics emitted by an application configured to send telemetry. | The OpenTelemetry for VS Code Marketplace listing describes an in-editor OTLP receiver for logs, traces, and metrics, with data held in memory on the machine and source-line links. It targets instrumented applications and multi-service debugging; it is not evidence that arbitrary, uninstrumented requests will be captured. Marketplace listing |
The Marketplace links above are generic listing URLs in the available source material and do not identify a specific extension listing. Do not treat the product descriptions as verified performance or coverage tests.
Design the source-to-request match
To place a measurement beside code, the extension needs a defensible association between an observed request and a source range. A timestamp alone does not identify which line initiated a call, especially when requests are concurrent, generated by a shared client, or made in another service. Decide how the extension obtains that association—such as instrumentation that records call-site context—and make unmatched requests visible as unmatched rather than pinning them to a guess.
- Define whether a displayed value belongs to an endpoint declaration, a call site, or a particular observed request.
- Clarify how repeated calls are represented: latest observation, a distribution, or another clearly defined summary.
- State which runtimes and client libraries are observed and which are not. A fetch recorder’s coverage does not imply coverage of other transports.
- Keep the timing definition visible. A client-observed duration is not automatically a server-side processing time.
- Offer a way to inspect the underlying request context without turning an inline label into an unexplained performance verdict.
Make “no cloud” a verifiable product behavior
“No dashboard” describes the interface; it does not establish that data stays local. Microsoft’s telemetry documentation says third-party extensions may collect their own usage data and are not controlled by telemetry.telemetryLevel. Users need to consult each extension’s documentation for its practices.
A credible local-only statement should specify whether the extension opens any network connections, what it stores and for how long, whether request or response contents are retained, how credentials are handled, and whether any telemetry is optional. Distinguish extension traffic from application traffic: an extension may store its own observations locally while the application still sends requests to remote APIs. Local processing claims made by other extension publishers do not establish the behavior of a new product.
Independent reader supportYour contribution helps us test, update, and keep practical guides available for everyone.What makes the idea distinct
Showing a measurement beside the relevant code may be a useful interface choice, but API timing is already available in VS Code through neighboring approaches: active probes, runtime request recording, and instrumented telemetry. The differentiator should therefore be specific: what data is captured, what is covered, how a reading maps to source, and what the number means. The available product descriptions provide no benchmark data for ranking the approaches’ speed or accuracy.
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