For Beginners: An Introduction to Reading and Utilizing Logs
Introduction
“I see an error, but I don't know where to look in the logs...”
“How should I actually use logs in the first place?”
“My eyes just glaze over when I see all that text...”
To those beginner engineers who feel this way:
Logs are like the “mutterings” of a system.
Once you learn how to read and utilize them correctly, your troubleshooting and development efficiency will change significantly.
In this article, I will share the basic knowledge and tips for reading logs so that you can transform them from something you
“just glance at” into a “tool useful for problem-solving.”
What are logs?
Logs are information recorded while a system is running.
📌 Main Types
🔍 Logs serve as clues to know “where,” “what,” and “when” something happened.
Basic mindset when reading logs
✅ 1. Follow in chronological order
Logs are usually recorded in “chronological order.”
First, you can get closer to the cause by following the “immediately before” and “immediately after” the error occurred.
✅ 2. Filter by keywords
Levels such as ERROR / WARN / INFO
Terms such as Exception, Timeout, NullPointer, StatusCode:500, etc.
Specific user IDs or request paths
🔍 Instead of “reading the whole thing,” the basic approach is to “narrow down and read the parts you are concerned about.”
✅ 3. Compare with the “normal flow”
Keep logs from when things were successful
Compare with the “logs from when it worked” for the same process
The fact that 'a log that should be there is missing' is also a hint
📘 Focusing on 'what is different' is the key to reading logs.
Specific techniques for 'utilizing' logs
🛠️ 1. Get used to 'structured logs' instead of console.log()
Example:
🧠 Developing the habit of recording 'where and what happened' in logs makes troubleshooting significantly easier.
🧪 2. 'Intentionally cause failures' during development to check logs
Deliberately trigger an authentication error
Try cases where DB values are empty
Check in advance how error logs appear
🧪 Learning 'how logs appear when this happens' through experience allows for immediate response in actual work.
🔍 3. List of 'hints' to look for in logs
Error codes (e.g., 500, 404, 401)
Stack traces (where the exception occurred)
Request URL/Method
Client IP/UserAgent
Execution time (tracking causes of performance issues)
What if you still don't understand after looking at the logs?
First, grasp 'what is recorded in which log'
Organize 'filtering conditions' such as time, URL, and request parameters“filtering conditions”
Consult with your seniors or team by saying, "I don't know how to read this log."
📣 Asking questions is also an important step in getting used to logs.
Conclusion
Logs might seem a bit intimidating for beginners.
However, once you learn how to use them, they become a weapon that dramatically improves your ability to solve problems on your own.
Don't try to read everything
Narrow down by timeline and keywords
Compare successful and failed attempts
Learn by doing through "experimentation"
Just by keeping these points in mind, logs will become something you can read.
I hope this serves as a catalyst for leveling up your error-solving skills.
Notice
At ZENSHIN, we support young professionals and beginners with
"How to develop log reading skills," "Basic training for incident response," and "Habitualizing operational thinking." and more.
Escalations are increasing because staff don't know how to read logs
Incident response is becoming too dependent on specific individuals
Want to help young staff acquire "operational skills"
If you are a company or team with these concerns, please feel free to consult with us.
👉 If you are interested, you can inquire via
https://www.zenshin-inc.co.jp/#contact
!
■ZENSHIN Company Overview
Trade Name: ZENSHIN Co., Ltd.
Address: 1-11-4 Jinnan, Shibuya-ku, Tokyo 150-0041
Representative: Motoki Hanzawa, Representative Director
Main Business:
・Contract development of casual games
・Contract development of software / systems
・Contract development of generative AI
・Quality assurance testing
・SES / Staffing and recruitment services