MockServer for VS Code

Author, record, and debug HTTP/HTTPS mocks without leaving your editor.

• Zero-config schema authoring — write expectation files with validation, completion, and hover, no language server to install.
• Record real traffic into code — turn proxied requests into loadable JSON or a MockServerClient Java DSL.
• Live dashboard inside the editor — watch requests arrive in a VS Code tab.

MockServer is an HTTP(S) mock server and proxy for testing. This extension brings the full authoring-to-debugging workflow into VS Code — and works against any running MockServer instance, with optional one-click Docker start/stop for local development.

Why you'll love it

Schema-driven authoring — no language server required

Validation, completion, enum suggestions, and hover docs the moment you name a file *.mockserver.json.

Name a file *.mockserver.json or *.mockserver.jsonc and the editor validates it against the same JSON schema MockServer uses internally. You get inline error squiggles, property autocompletion, enum suggestions, and hover documentation without ever starting the server. A file may hold a single expectation object or an array (initialization JSON); .jsonc files allow comments and trailing commas.

Record real traffic into code — the fast path to a mock

Proxy real traffic, then save what MockServer recorded as loadable JSON or a ready-to-paste Java DSL.

Point MockServer at a real upstream as a proxy, exercise your app, then run Save Recorded Expectations (JSON or Java). Choose JSON to get a *.mockserver.json file you can load straight back in, or Java to get a MockServerClient DSL you can paste into a test. If nothing has been proxied yet, the command tells you instead of opening an empty file — no guessing.

MockServer side panel + docked dashboard

A MockServer view in the Activity Bar puts every action one click away, and the live dashboard docks in the bottom panel — all inside VS Code, none of it mixed in with your editor tabs.

Click the MockServer icon in the Activity Bar for a panel of grouped, one-click actions — Server (start / dashboard / reset), Author (load / record / generate from OpenAPI), Inspect (send request / request log / drift / trace), and WASM — with a status line showing the configured localhost:<port>. Run Open Dashboard to reveal the real MockServer dashboard docked in the bottom panel (its own "MockServer Dashboard" view — active expectations, the request log, and live traffic, full width and separate from your code tabs). Prefer your browser? Open Dashboard in Browser opens the same URL there.

30-second quick start

1. Create login.mockserver.json — the editor validates the schema as you type.
2. Start a server: run MockServer: Start (Docker) for a local container, MockServer: Start (binary, no Docker) if you don't have Docker, or point the extension at an already-running server by setting mockserver.port (and mockserver.dockerImage / mockserver.containerName if relevant).
3. Load it: click the Load into running MockServer CodeLens at the top of the file (also in the editor title bar and right-click menu) to push your expectation(s) to the server.
4. Watch it: run MockServer: Open Dashboard (or click the status item in the MockServer side panel) and send a request to see it arrive in the docked dashboard.

Open the MockServer view in the Activity Bar for one-click access to every action, and a MockServer :<port> entry sits in the status bar — click it any time for a quick menu of the most common actions (Open Dashboard, Start, Stop, View Request Log).

Prerequisites

• VS Code 1.80+
• Docker Desktop — only for Start (Docker) / Stop. No Docker? Use Start (binary, no Docker) instead, which runs a self-contained bundle (no Docker or JDK needed). Every other command works against any running MockServer instance.

Installation

Install from the VS Code Marketplace or search for MockServer in the Extensions view. For Open VSX (Eclipse Theia, Gitpod, etc.), install from open-vsx.org.

Everything the extension does

Expectation files — CodeLens, menus, and snippets

At the top of every expectation file two CodeLens actions appear:

Both are also Command Palette commands. The same file-scoped actions appear in the editor title bar and the right-click (editor context) menu whenever a *.mockserver.json, *.mockserver.jsonc, or *.mockserver-request.json file is open, and are hidden from the Command Palette when no matching file is active.

Snippets — in any .json or .jsonc file, type a prefix and press Tab:

Generate and record expectations

Inspect and control

Test/code-aware gutters

Open a Java, Kotlin, JS/TS, Groovy, or Scala file that uses MockServer and a run/inspect CodeLens appears above each usage site it finds — new MockServerClient(...), a JUnit 5 @MockServerSettings annotation, or a Testcontainers MockServerContainer. Clicking it reveals the docked dashboard for the configured instance. Detection is a best-effort regex scan, not a full parse, so an occasional extra lens is harmless.

In-IDE HTTP debugger (breakpoints)

Pause real traffic flowing through MockServer and inspect/modify it without leaving the editor.

Prerequisite: breakpoints fire only on traffic flowing through MockServer — proxied/forwarded exchanges, matched mock responses, and the unmatched-404 path. Point your app at MockServer as a proxy or mock endpoint first; this is not a JVM-style attach to an arbitrary process.

When a matching request flows through MockServer, the paused exchange appears in the panel:

• REQUEST phase — Continue (forward the original), Modify (edit the request JSON, then forward), or Abort (write a response downstream without forwarding). Abort is REQUEST-phase only.
• RESPONSE phase — Continue (write the original response) or Modify (edit the response JSON).
• Stream frames (SSE/chunked/gRPC/WebSocket) — per frame: Continue / Modify / Inject / Drop / Close (frame bodies are Base64).

The server's safety rails apply unchanged: paused exchanges auto-continue after breakpointTimeoutMillis (30s default), at most breakpointMaxHeld (50) are held at once, and disconnecting the panel cleans up the debugger's matchers.

LLM authoring, call graph, chaos, and contract tests

Inside an httpLlmResponse block of a *.mockserver.json file you also get authoring completion for provider names, representative model names, and the block's fields.

Dashboard

WASM custom rules

MockServer supports WebAssembly custom-rule modules for body matching (requires wasmEnabled=true on the server). Manage modules without leaving VS Code:

Once uploaded, reference a module in an expectation body matcher:

{
  "httpRequest": {
    "body": { "type": "WASM", "moduleName": "myRule" }
  },
  "httpResponse": { "statusCode": 200 }
}

If WASM support is disabled on the server, the server's own error message is surfaced verbatim.

Server lifecycle

The download uses VS Code's built-in fetch, so it honours the editor's http.proxy / system-proxy settings and works behind a corporate proxy without extra configuration. Checksum verification against the published .sha256 sidecar is fail-closed: a mismatch always aborts, and if the sidecar can't be fetched (common behind a TLS-inspection proxy) you must explicitly confirm before the bundle installs unverified.

Command reference

All commands are available from the Command Palette (Cmd+Shift+P / Ctrl+Shift+P) by typing "MockServer".

Settings

File conventions

Scratch request file format (*.mockserver-request.json):

{
  "method": "GET",
  "path": "/api/resource",
  "headers": { "Accept": "application/json" },
  "body": ""
}

method and path are required; headers and body are optional.

Try it locally

From the repo root, one command builds the extension, starts a local MockServer, loads sample files, and opens a sandboxed VS Code Extension Development Host — nothing to install or uninstall:

scripts/try-editor-extensions.sh           # VS Code Extension Development Host
scripts/try-editor-extensions.sh --install # or install the packaged .vsix into your VS Code

Building from source

npm install
npm run compile
npm test

Packaging

npx vsce package

Produces a .vsix file installable via code --install-extension mockserver-*.vsix.

Links

• Website: www.mock-server.com
• Source: github.com/mock-server/mockserver (mockserver-vscode)
• Issues: github.com/mock-server/mockserver/issues
• License: Apache-2.0