FastLog — Free Local Log Viewer | JSON, NDJSON, Offline Search
FastLog

The log viewer developers actually want.

Search millions of lines instantly. JSON & NDJSON support, date filtering, regex — 100% local in your browser.

Open AppSee Features
⚡ Indexed Search🔒 100% Local{ } JSON & NDJSON📱 PWA Ready
https://fastlogviewer.com/app
FastLog Viewer — local log file viewer with indexed search, JSON expansion, and log level filtering

Built for debugging at scale.

Indexed search, structured JSON view, and AI analysis — instant, local, and private.

Indexed Search

Instant results across millions of lines with regex, case-sensitive, and whole-word support.

JSON & NDJSON Support

Toggle between plain text and structured views. Every JSON field is fully expandable and readable.

Coming Soon

AI Log Analysis

Let AI explain cryptic errors, detect anomalies, and suggest fixes directly from your log viewer.

100% Local & Private

No servers, no accounts, no telemetry. Your logs never leave your machine.

Date Range Filtering

Automatic timestamp detection across all common formats for precise time-based filtering.

PWA — Works Offline

Install FastLog as a desktop app. It is fully offline capable and works anywhere.

How it works

From raw logs to answers in seconds.

01

Drop your log file

Drag and drop any .log, .txt, .json, or .ndjson file. No uploads — everything stays local.

02

Search & filter instantly

Indexed on load for millisecond results. Use regex, date ranges, or log level filters.

03

Find the root cause

Expand JSON fields, trace stack traces, and pinpoint issues in seconds.

Coming Soon

Your logs, explained by AI.

Stop guessing what cryptic error messages mean. FastLog's upcoming AI integration will analyze your logs, explain the root cause, and suggest actionable fixes — right inside the viewer.

Be the first to know when AI-powered log analysis lands.

AI Analysis
Preview
Selected Log
[ERROR] Failed to fetch user profile: Connection timeout at fetchUserProfile (/src/services/user.ts:42:15)

This error indicates that the application attempted to retrieve a user profile from the database or an external API, but the connection timed out before a response was received.

Root Cause Analysis

  • The database server might be down or experiencing high load.
  • There could be a network connectivity issue between the application server and the database.
  • The timeout threshold configured in /src/services/user.ts might be too aggressive.

Suggested Fix

const response = await fetch('/api/users/profile', {
  signal: AbortSignal.timeout(5000) // Increase from 1000ms
});

Simple pricing. Start today.

Every feature, every file — no account needed.

Free

$0

Everything you need to view, search, and analyze logs locally.

  • Unlimited log files
  • Indexed search & filtering
  • JSON & NDJSON support
  • Date range filtering
  • PWA — install & use offline
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Frequently Asked Questions