TemplateNotFound: index.html

TemplateNotFound: index.html

$ flask run
Traceback (most recent call last):
  ...
jinja2.exceptions.TemplateNotFound: index.html

Why this happens

Flask searches for templates in the templates/ folder relative to the application or blueprint. Wrong filenames, missing directories, or custom template_folder misconfigurations cause this error.

Fix

• Create a templates/ directory and place index.html inside.
• If using blueprints, ensure their template_folder is correctly set or use absolute paths.

Wrong code

from flask import Flask, render_template
app = Flask(__name__)

@app.route("/")
def index():
    return render_template("index.htm")  # wrong filename

Fixed code

from flask import Flask, render_template
app = Flask(__name__)

@app.route("/")
def index():
    return render_template("index.html")