diff --git a/packages/mockotlpserver/db/README.md b/packages/mockotlpserver/db/README.md
index 66ad2fb2..1d8cd94c 100644
--- a/packages/mockotlpserver/db/README.md
+++ b/packages/mockotlpserver/db/README.md
@@ -1,3 +1,3 @@
 # UI traces folder
 
-this folder is to place all the traces data we want to plt in the web ui.
\ No newline at end of file
+this folder is to place all the traces data we want to plot in the web ui.
\ No newline at end of file
diff --git a/packages/mockotlpserver/lib/cli.js b/packages/mockotlpserver/lib/cli.js
index a0523d89..0b2ed54b 100755
--- a/packages/mockotlpserver/lib/cli.js
+++ b/packages/mockotlpserver/lib/cli.js
@@ -24,7 +24,7 @@
 const dashdash = require('dashdash');
 
 const luggite = require('./luggite');
-const {JSONPrinter, InspectPrinter} = require('./printers');
+const {JSONPrinter, InspectPrinter, FilePrinter} = require('./printers');
 const {TraceWaterfallPrinter} = require('./waterfall');
 const {MetricsSummaryPrinter} = require('./metrics-summary');
 const {LogsSummaryPrinter} = require('./logs-summary');
@@ -50,10 +50,19 @@ const PRINTER_NAMES = [
     'metrics-summary',
     'logs-summary',
     'summary',
+
+    'trace-file', // saving into fs for UI and other processing
 ];
 
-// This adds a custom cli option type to dashdash, to support `-o json,waterfall`
-// options for specifying multiple printers (aka output modes).
+/**
+ * This adds a custom cli option type to dashdash, to support `-o json,waterfall`
+ * options for specifying multiple printers (aka output modes).
+ *
+ * @param {any} option
+ * @param {string} optstr
+ * @param {string} arg
+ * @returns {Array<string>}
+ */
 function parseCommaSepPrinters(option, optstr, arg) {
     const printers = arg
         .trim()
@@ -97,6 +106,11 @@ const OPTIONS = [
         type: 'string',
         help: `The hostname on which servers should listen, by default this is "${DEFAULT_HOSTNAME}".`,
     },
+    {
+        names: ['ui'],
+        type: 'bool',
+        help: 'Start a web server to inspect traces with some charts.',
+    },
 ];
 
 async function main() {
@@ -121,17 +135,30 @@ async function main() {
         process.exit(0);
     }
 
+    /** @type {Array<'http'|'grpc'|'ui'>} */
+    const services = ['http', 'grpc'];
+    /** @type {Array<string>} */
+    const outputs = opts.o;
+
+    if (opts.ui) {
+        services.push('ui');
+        outputs.push('trace-file');
+    }
+
     const otlpServer = new MockOtlpServer({
         log,
-        services: ['http', 'grpc', 'ui'],
+        services,
         grpcHostname: opts.hostname || DEFAULT_HOSTNAME,
         httpHostname: opts.hostname || DEFAULT_HOSTNAME,
         uiHostname: opts.hostname || DEFAULT_HOSTNAME,
     });
     await otlpServer.start();
 
+    // Avoid duplication of printers
+    const printersSet = new Set(outputs);
     const printers = [];
-    opts.o.forEach((printerName) => {
+
+    printersSet.forEach((printerName) => {
         switch (printerName) {
             case 'trace-inspect':
                 printers.push(new InspectPrinter(log, ['trace']));
@@ -186,6 +213,10 @@ async function main() {
             case 'logs-summary':
                 printers.push(new LogsSummaryPrinter(log));
                 break;
+
+            case 'trace-file':
+                printers.push(new FilePrinter(log));
+                break;
         }
     });
     printers.forEach((p) => p.subscribe());
diff --git a/packages/mockotlpserver/lib/printers.js b/packages/mockotlpserver/lib/printers.js
index 46e6bb31..25048b12 100644
--- a/packages/mockotlpserver/lib/printers.js
+++ b/packages/mockotlpserver/lib/printers.js
@@ -26,6 +26,9 @@
  *      printer.subscribe();
  */
 
+const fs = require('fs');
+const path = require('path');
+
 const {
     diagchSub,
     CH_OTLP_V1_LOGS,
@@ -153,8 +156,63 @@ class JSONPrinter extends Printer {
     }
 }
 
+/**
+ * This printer converts to a possible JSON representation of each service
+ * request and saves it to a file. **Warning**: Converting OTLP service requests to JSON is fraught.
+ */
+class FilePrinter extends Printer {
+    constructor(
+        log,
+        indent,
+        signals = ['trace'],
+        dbDir = path.resolve(__dirname, '../db')
+    ) {
+        super(log);
+        this._indent = indent || 0;
+        this._signals = signals;
+        this._dbDir = dbDir;
+    }
+    printTrace(trace) {
+        if (!this._signals.includes('trace')) return;
+        const str = jsonStringifyTrace(trace, {
+            indent: this._indent,
+            normAttributes: true,
+        });
+        const normTrace = JSON.parse(str);
+        const tracesMap = new Map();
+        normTrace.resourceSpans.forEach((resSpan) => {
+            resSpan.scopeSpans.forEach((scopeSpan) => {
+                scopeSpan.spans.forEach((span) => {
+                    let traceSpans = tracesMap.get(span.traceId);
+
+                    if (!traceSpans) {
+                        traceSpans = [];
+                        tracesMap.set(span.traceId, traceSpans);
+                    }
+                    traceSpans.push(span);
+                });
+            });
+        });
+
+        // Group all spans from the same trace into an ndjson file.
+        for (const [traceId, traceSpans] of tracesMap.entries()) {
+            const filePath = path.join(this._dbDir, `trace-${traceId}.ndjson`);
+            const stream = fs.createWriteStream(filePath, {
+                flags: 'a',
+                encoding: 'utf-8',
+            });
+
+            for (const span of traceSpans) {
+                stream.write(JSON.stringify(span) + '\n');
+            }
+            stream.close();
+        }
+    }
+}
+
 module.exports = {
     Printer,
     JSONPrinter,
     InspectPrinter,
+    FilePrinter,
 };
diff --git a/packages/mockotlpserver/lib/ui.js b/packages/mockotlpserver/lib/ui.js
index f3ab29cd..41eedca7 100644
--- a/packages/mockotlpserver/lib/ui.js
+++ b/packages/mockotlpserver/lib/ui.js
@@ -21,101 +21,10 @@ const fs = require('fs');
 const path = require('path');
 const http = require('http');
 
-const Long = require('long');
-
-const {Printer} = require('./printers');
 const {Service} = require('./service');
 
 // helper functions
 
-/**
- * @typedef {Object} SpanTree
- * @property {import('./types').Span} span
- * @property {import('./types').Span[]} children
- */
-
-/**
- * @typedef {Object} TraceTree
- * @property {string} id
- * @property {SpanTree[]} children
- */
-
-class UiPrinter extends Printer {
-    constructor(log) {
-        super(log);
-        this._dbDir = path.resolve(__dirname, '../db');
-    }
-
-    /**
-     * Prints into files the spns belonging to a trace
-     * @param {import('./types').ExportTraceServiceRequest} traceReq
-     */
-    printTrace(traceReq) {
-        /** @type {Map<string, import('./types').Span[]>} */
-        const tracesMap = new Map();
-
-        // Group all spans by trace
-        traceReq.resourceSpans.forEach((resSpan) => {
-            resSpan.scopeSpans.forEach((scopeSpan) => {
-                scopeSpan.spans.forEach((span) => {
-                    const traceId = span.traceId.toString('hex');
-                    let traceSpans = tracesMap.get(traceId);
-
-                    if (!traceSpans) {
-                        traceSpans = [];
-                        tracesMap.set(traceId, traceSpans);
-                    }
-                    traceSpans.push(span);
-                });
-            });
-        });
-
-        // Write into a file
-        // TODO: manage lifetime of old trace ndjson files.
-        for (const [traceId, traceSpans] of tracesMap.entries()) {
-            const filePath = path.join(this._dbDir, `trace-${traceId}.ndjson`);
-            const stream = fs.createWriteStream(filePath, {
-                flags: 'a',
-                encoding: 'utf-8',
-            });
-
-            for (const span of traceSpans) {
-                const formatted = this._formatSpan(span);
-                stream.write(
-                    JSON.stringify(Object.assign({}, span, formatted)) + '\n'
-                );
-            }
-            stream.close();
-        }
-    }
-
-    /**
-     * @param {import('./types').Span} span
-     */
-    _formatSpan(span) {
-        const traceId = span.traceId.toString('hex');
-        const spanId = span.spanId.toString('hex');
-        const parentSpanId = span.parentSpanId?.toString('hex');
-        const formatted = {traceId, spanId};
-
-        if (parentSpanId) {
-            formatted.parentSpanId = parentSpanId;
-        }
-        formatted.startTimeUnixNano = new Long(
-            span.startTimeUnixNano.low,
-            span.startTimeUnixNano.high,
-            span.startTimeUnixNano.unsigned
-        ).toString();
-        formatted.endTimeUnixNano = new Long(
-            span.endTimeUnixNano.low,
-            span.endTimeUnixNano.high,
-            span.endTimeUnixNano.unsigned
-        ).toString();
-
-        return formatted;
-    }
-}
-
 /**
  * @param {http.ServerResponse} res
  */
@@ -152,7 +61,6 @@ class UiService extends Service {
         super();
         this._opts = opts;
         this._server = null;
-        this._printer = new UiPrinter(opts.log);
     }
 
     async start() {
@@ -170,9 +78,18 @@ class UiService extends Service {
                     const traceFiles = fs.readdirSync(dataPath).filter((f) => {
                         return f.startsWith('trace-');
                     });
+                    const sortedFiles = traceFiles.sort((fileA, fileB) => {
+                        const statA = fs.statSync(`${dataPath}/${fileA}`);
+                        const statB = fs.statSync(`${dataPath}/${fileB}`);
+
+                        return (
+                            new Date(statB.birthtime).getTime() -
+                            new Date(statA.birthtime).getTime()
+                        );
+                    });
 
                     res.writeHead(200, {'Content-Type': 'application/json'});
-                    res.end(JSON.stringify(traceFiles));
+                    res.end(JSON.stringify(sortedFiles));
                     return;
                 } else if (req.url.startsWith('/api/traces/')) {
                     const traceId = req.url.replace('/api/traces/', '');
@@ -211,8 +128,6 @@ class UiService extends Service {
             });
         });
 
-        this._printer.subscribe();
-
         return new Promise((resolve, reject) => {
             this._server.listen(port, hostname, () => {
                 resolve();