Microsoft IIS W3C Analyzer
Full support for IIS W3C Extended logs. Automatically maps date, time, client IP, method, URI stem, status, substatus, win32 status, and time-taken.
Upload or paste any .log file to view, search, and analyze entries. Specialized support for Microsoft IIS W3C logs, HTTP status code filtering (2xx, 3xx, 4xx, 5xx), table view, and CSV export.
Supports IIS W3C, Apache, Nginx, .log, .txt, .out, .err — up to 50 MB
Files are processed entirely in your browser. Nothing is uploaded to any server.
| # | Date & Time | Client IP | Method | URI Stem / Path | Status | Sub | Win32 | Time (ms) | User Agent / Query |
|---|
From instant error detection to smart search — built for developers, sysadmins, and QA engineers.
Full support for IIS W3C Extended logs. Automatically maps date, time, client IP, method, URI stem, status, substatus, win32 status, and time-taken.
One-click filtering by 2xx Success, 3xx Redirection, 4xx Client Error, and 5xx Server Error, plus specific status code selectors (200, 301, 401, 403, 404, 500).
Switch seamlessly between a columnar structured data table with sticky headers and a terminal-style monospace raw text viewer.
Discover top requested URLs, top client IPs, status breakdown percentages, and server latency metrics (average & slowest time-taken).
Automatically identifies ERROR, WARN, INFO, and DEBUG levels with colored highlighting, HTTP badge counters, and severity counts.
Instant keyword search with match highlighting. Wrap queries in /slashes/ for full regular expressions to filter exact URLs or IPs.
Download filtered rows as a clean CSV spreadsheet with headers, structured JSON array, or plain text file with one click.
Confidential logs never leave your device. All parsing, filtering, and analysis runs completely inside your browser client.
Handles log files up to 50 MB with an optimized batch rendering engine that maintains butter-smooth browser responsiveness.
Four quick steps from upload to root cause analysis — free, private, no software required.
Drag your .log file into the drop zone, browse from your computer, or paste raw IIS/Apache lines directly into the text box.
View log lines in classic Raw terminal mode with syntax coloring, or toggle to the structured Table View for columnar IIS data.
Click status pills (2xx, 3xx, 4xx, 5xx) or select specific codes like 404 Not Found or 500 Internal Error to isolate anomalies in seconds.
Export the filtered subset as CSV for Excel analysis, JSON for programmatic pipelines, or plain TXT for team bug tickets.
Microsoft Internet Information Services (IIS) generates W3C Extended formatted log files recording every incoming HTTP request. These logs typically reside in C:\inetpub\logs\LogFiles\W3SVC* and document essential telemetry including client IP addresses, requested URIs, HTTP methods, server response codes (sc-status), IIS substatus codes (sc-substatus), Windows system error codes (sc-win32-status), and request duration in milliseconds (time-taken).
Opening multi-gigabyte or hundreds-of-megabyte IIS log files in generic text editors like Notepad often leads to sluggish performance or application crashes. Our free online log viewer provides dedicated IIS intelligence: paste or upload your log file and the viewer automatically maps the #Fields header, parses columnar data, and presents both a color-coded raw text view and an interactive structured table view.
When diagnosing website downtime, bot attacks, or API failures, hunting line-by-line is inefficient. Our log viewer equips you with dedicated HTTP status code filters:
• 2xx Success (200, 201, 204, 206): Valid requests served normally by your web application.
• 3xx Redirection (301, 302, 304, 307, 308): Permanent or temporary URL redirects, as well as browser cache revalidation (304 Not Modified).
• 4xx Client Errors (400, 401, 403, 404, 429): Missing pages, broken internal links, expired sessions, access violations, or rate-limited bots.
• 5xx Server Errors (500, 502, 503, 504): Critical application crashes, unhandled backend exceptions, gateway timeouts, or IIS application pool crashes.
You can also use the specific status code selector to isolate exact codes like 404 or 500, and view an instant visual proportion bar depicting the percentage distribution of your server's traffic.
One of the most powerful features of Microsoft IIS logs is the combination of sc-substatus and sc-win32-status. Standard HTTP status codes alone often don't provide the complete diagnostic picture. For example, an HTTP 403 error could be caused by directory browsing restrictions (403.14), an invalid client certificate (403.7), or an IP address denial rule (403.6). Similarly, an HTTP 404.0 indicates a missing file, whereas 404.13 points to IIS Request Filtering blocking an oversized payload.
The table view in this tool includes built-in explanatory tooltips for common substatus codes and Windows Win32 error codes (such as Win32 code 0 for success, 2 for file not found, 5 for access denied, 64 for network name unavailable due to client disconnects, and 1326 for invalid logon credentials). This allows DevOps teams and sysadmins to identify the exact root cause without consulting external documentation.
Beyond troubleshooting errors, log analysis provides critical traffic insights. The built-in Insights & Forensics panel automatically aggregates your log data to reveal:
1. Top Requested Endpoints: Identify high-traffic endpoints, frequently visited APIs, and potential brute-force targets.
2. Top Client IPs: Spot aggressive web scrapers, crawler bots, or DDoS sources scanning for vulnerable files.
3. Latency Analysis: If your IIS log includes the time-taken field, the tool calculates average response time, peak latency, and highlights requests taking longer than 1,000 milliseconds.
Clicking any URL, IP, or status code in the insights panel immediately applies an interactive filter, streamlining your debugging workflow.
Everything you need to know about opening and analyzing IIS and server logs online.
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