diff --git a/packages/mongodb-runner/src/cli.ts b/packages/mongodb-runner/src/cli.ts
index 633eb19a..ca6c4194 100644
--- a/packages/mongodb-runner/src/cli.ts
+++ b/packages/mongodb-runner/src/cli.ts
@@ -79,6 +79,10 @@ import type { MongoClientOptions } from 'mongodb';
     })
     .option('debug', { type: 'boolean', describe: 'Enable debug output' })
     .option('verbose', { type: 'boolean', describe: 'Enable verbose output' })
+    .option('json', {
+      type: 'boolean',
+      describe: 'Output machine-readable JSON ("ls" only)',
+    })
     .command('start', 'Start a MongoDB instance')
     .command('stop', 'Stop a MongoDB instance')
     .command('prune', 'Clean up metadata for any dead MongoDB instances')
@@ -149,8 +153,18 @@ import type { MongoClientOptions } from 'mongodb';
   }
 
   async function ls() {
-    for await (const { id, connectionString } of utilities.instances(argv)) {
-      console.log(`${id}: ${connectionString}`);
+    if (argv.json) {
+      let first = true;
+      for await (const { serialized, ...rest } of utilities.instances(argv)) {
+        console.log(first ? '[' : ',');
+        first = false;
+        console.log(JSON.stringify({ ...rest, ...serialized }, null, 2));
+      }
+      console.log(']');
+    } else {
+      for await (const { id, connectionString } of utilities.instances(argv)) {
+        console.log(`${id}: ${connectionString}`);
+      }
     }
   }
 
diff --git a/packages/mongodb-runner/src/index.ts b/packages/mongodb-runner/src/index.ts
index d59500c9..8de43d89 100644
--- a/packages/mongodb-runner/src/index.ts
+++ b/packages/mongodb-runner/src/index.ts
@@ -2,6 +2,7 @@ export {
   MongoServer,
   type MongoServerEvents,
   MongoServerOptions,
+  SerializedServerProperties as MongoServerSerializedProperties,
 } from './mongoserver';
 export {
   MongoCluster,
@@ -12,6 +13,7 @@ export {
   RSOptions as MongoClusterRSOptions,
   CommonOptions as MongoClusterCommonOptions,
   ShardedOptions as MongoClusterShardedOptions,
+  SerializedClusterProperties as MongoClusterSerializedProperties,
 } from './mongocluster';
 export type { LogEntry } from './mongologreader';
 export type { ConnectionString } from 'mongodb-connection-string-url';
diff --git a/packages/mongodb-runner/src/mongocluster.ts b/packages/mongodb-runner/src/mongocluster.ts
index d8d97388..df239fb6 100644
--- a/packages/mongodb-runner/src/mongocluster.ts
+++ b/packages/mongodb-runner/src/mongocluster.ts
@@ -1,4 +1,8 @@
-import type { MongoServerEvents, MongoServerOptions } from './mongoserver';
+import type {
+  MongoServerEvents,
+  MongoServerOptions,
+  SerializedServerProperties,
+} from './mongoserver';
 import { MongoServer } from './mongoserver';
 import { ConnectionString } from 'mongodb-connection-string-url';
 import type { DownloadOptions } from '@mongodb-js/mongodb-downloader';
@@ -162,6 +166,17 @@ export type MongoClusterEvents = {
   removeListener: [keyof MongoClusterEvents];
 };
 
+export interface SerializedClusterProperties {
+  topology: MongoClusterOptions['topology'];
+  replSetName?: string;
+  servers: SerializedServerProperties[];
+  shards: SerializedClusterProperties[];
+  oidcMockProviderProcess?: ReturnType<OIDCMockProviderProcess['serialize']>;
+  defaultConnectionOptions: Partial<MongoClientOptions>;
+  users: MongoDBUserDoc[];
+  options?: MongoClusterOptions;
+}
+
 function removePortArg([...args]: string[]): string[] {
   let portArgIndex = -1;
   if ((portArgIndex = args.indexOf('--port')) !== -1) {
@@ -278,6 +293,7 @@ export class MongoCluster extends EventEmitter<MongoClusterEvents> {
   private oidcMockProviderProcess?: OIDCMockProviderProcess;
   private defaultConnectionOptions: Partial<MongoClientOptions> = {};
   private users: MongoDBUserDoc[] = [];
+  private originalOptions?: MongoClusterOptions;
 
   private constructor() {
     super();
@@ -309,7 +325,7 @@ export class MongoCluster extends EventEmitter<MongoClusterEvents> {
     });
   }
 
-  serialize(): unknown /* JSON-serializable */ {
+  serialize(): SerializedClusterProperties {
     return {
       topology: this.topology,
       replSetName: this.replSetName,
@@ -318,6 +334,7 @@ export class MongoCluster extends EventEmitter<MongoClusterEvents> {
       oidcMockProviderProcess: this.oidcMockProviderProcess?.serialize(),
       defaultConnectionOptions: jsonClone(this.defaultConnectionOptions ?? {}),
       users: jsonClone(this.users),
+      options: jsonClone(this.originalOptions),
     };
   }
 
@@ -328,7 +345,9 @@ export class MongoCluster extends EventEmitter<MongoClusterEvents> {
     return true;
   }
 
-  static async deserialize(serialized: any): Promise<MongoCluster> {
+  static async deserialize(
+    serialized: SerializedClusterProperties,
+  ): Promise<MongoCluster> {
     const cluster = new MongoCluster();
     cluster.topology = serialized.topology;
     cluster.replSetName = serialized.replSetName;
@@ -343,6 +362,7 @@ export class MongoCluster extends EventEmitter<MongoClusterEvents> {
     cluster.oidcMockProviderProcess = serialized.oidcMockProviderProcess
       ? OIDCMockProviderProcess.deserialize(serialized.oidcMockProviderProcess)
       : undefined;
+    cluster.originalOptions = serialized.options;
     return cluster;
   }
 
@@ -380,6 +400,7 @@ export class MongoCluster extends EventEmitter<MongoClusterEvents> {
     options = { ...options, ...(await handleTLSClientKeyOptions(options)) };
 
     const cluster = new MongoCluster();
+    cluster.originalOptions = options;
     cluster.topology = options.topology;
     cluster.users = options.users ?? [];
     cluster.defaultConnectionOptions = { ...options.internalClientOptions };
diff --git a/packages/mongodb-runner/src/mongoserver.ts b/packages/mongodb-runner/src/mongoserver.ts
index 99dd9abb..a57a9c84 100644
--- a/packages/mongodb-runner/src/mongoserver.ts
+++ b/packages/mongodb-runner/src/mongoserver.ts
@@ -53,7 +53,7 @@ export interface MongoServerOptions {
   keyFileContents?: string;
 }
 
-interface SerializedServerProperties {
+export interface SerializedServerProperties {
   _id: string;
   pid?: number;
   port?: number;
@@ -66,6 +66,7 @@ interface SerializedServerProperties {
   isMongos?: boolean;
   isConfigSvr?: boolean;
   keyFileContents?: string;
+  commandline?: string[];
 }
 
 export interface MongoServerEvents {
@@ -98,6 +99,7 @@ export class MongoServer extends EventEmitter<MongoServerEvents> {
   private isConfigSvr = false;
   private keyFileContents?: string;
   private defaultConnectionOptions?: Partial<MongoClientOptions>;
+  private commandline: string[] = [];
 
   get id(): string {
     return this.uuid;
@@ -122,6 +124,7 @@ export class MongoServer extends EventEmitter<MongoServerEvents> {
       isMongos: this.isMongos,
       isConfigSvr: this.isConfigSvr,
       keyFileContents: this.keyFileContents,
+      commandline: this.commandline,
     };
   }
 
@@ -140,6 +143,7 @@ export class MongoServer extends EventEmitter<MongoServerEvents> {
     srv.isMongos = !!serialized.isMongos;
     srv.isConfigSvr = !!serialized.isConfigSvr;
     srv.keyFileContents = serialized.keyFileContents;
+    srv.commandline = serialized.commandline ?? [];
     if (!srv.closing) {
       srv.pid = serialized.pid;
       srv.dbPath = serialized.dbPath;
@@ -261,6 +265,7 @@ export class MongoServer extends EventEmitter<MongoServerEvents> {
 
     debug('starting server', commandline);
     const [executable, ...args] = commandline;
+    srv.commandline = commandline;
     const proc = spawn(executable, args, {
       stdio: ['inherit', 'pipe', 'pipe'],
       cwd: options.tmpDir,
diff --git a/packages/mongodb-runner/src/runner-helpers.ts b/packages/mongodb-runner/src/runner-helpers.ts
index 367aebb3..11285253 100644
--- a/packages/mongodb-runner/src/runner-helpers.ts
+++ b/packages/mongodb-runner/src/runner-helpers.ts
@@ -1,6 +1,9 @@
 import { BSON } from 'mongodb';
 import path from 'path';
-import type { MongoClusterOptions } from './mongocluster';
+import type {
+  MongoClusterOptions,
+  SerializedClusterProperties,
+} from './mongocluster';
 import { MongoCluster } from './mongocluster';
 import { parallelForEach } from './util';
 import * as fs from 'fs/promises';
@@ -10,7 +13,7 @@ import { once } from 'events';
 interface StoredInstance {
   id: string;
   filepath: string;
-  serialized: string;
+  serialized: SerializedClusterProperties;
   connectionString: string;
 }
 
@@ -31,7 +34,7 @@ export async function start(
     ...argv,
     args,
   });
-  const serialized = await cluster.serialize();
+  const serialized = cluster.serialize();
   const { connectionString } = cluster;
 
   await fs.writeFile(