FastLog — Free Fast Log Viewer | JSON, NDJSON, Regex & Offline Search
FastLog

The Free Log Viewer Developers Actually Want.

Search massive log files instantly with FastLog. JSON & NDJSON support, date filtering, regex — 100% local in your browser.

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⚡ 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.

The fastest log viewer in your browser — private, instant, and free.

Indexed Search

Instant results across massive log files 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 FastLog 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, no accounts — everything stays local on your machine.

02

Search & filter instantly

FastLog indexes your file on load for instant results. Use regex, date ranges, log-level filters, or plain-text search — whatever gets you there fastest.

03

Find the root cause

Expand JSON fields, trace stack traces, and pinpoint issues across massive log files in seconds. This is what a fast log viewer feels like.

Drop Your First Log

Why developers choose FastLog.

Fast. Free. Private. No compromises.

Instant search
Indexed on open — regex, date, or plain text.
100% local
No cloud uploads. No sign-up. No telemetry.
Every format
.log, .txt, .json, .ndjson — out of the box.
Works offline
Install as a PWA — fully offline capable.

Most log viewers force a trade-off between speed and privacy. FastLog indexes your file the moment you open it — so every search returns instantly — and everything runs locally in your browser. Your logs never touch a server.

Built for every developer's workflow.

From debugging to DevOps — one fast log viewer for all of it.

Backend & Full-Stack Developers

Search application logs, filter by log level, and expand JSON fields during debugging — without waiting on uploads or wrangling a desktop app.

DevOps & Platform Engineers

Review CI/CD pipeline output, inspect server error logs, and analyze deployment traces locally, keeping sensitive infrastructure data off third-party servers.

QA & Test Engineers

Open test run logs, search for failed assertions, and correlate application errors — all inside a fast, free log viewer that needs zero configuration.

Security Analysts

Examine audit logs and access logs in a completely private environment. Because FastLog is 100% local, it's the only log viewer safe to use with sensitive forensic data.

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
});

Start debugging, not onboarding.

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
Start Viewing Logs

Frequently Asked Questions