Profiling

Profile slow FastAPI requests with PyInstrument. It is off by default.

Turn it on

Enable it

In apps/api/.env:

ENABLE_PROFILING=true
PROFILING_SAMPLE_RATE=0.1

Restart the API

Restart mise dev, then look for the PyInstrument profiling line in the startup logs.

Profile a request

Add ?profile=1 to any request. You get an HTML report instead of JSON.

curl "http://localhost:8000/api/v1/user/me?profile=1" > profile.html

With mise dev --agent running, no sign-in header is needed.

Options

Variable	Default	What it does
`ENABLE_PROFILING`	`false`	Master switch
`PROFILING_SAMPLE_RATE`	`1.0`	Fraction of requests profiled in the background. Results go to the logs. Clients still get normal JSON

The default sample rate profiles every request. Lower it whenever you enable profiling: 0.1 for development, 0.01 for production. Use 0.0 for manual ?profile=1 only.

?profile= accepts 1, true, or yes.

Troubleshooting

Problem	Fix
Nothing happens	Check `ENABLE_PROFILING=true` and restart the API
Too slow	Lower `PROFILING_SAMPLE_RATE`

Start here

Everyday work

Go deeper

Reference

Turn it on

Options

Troubleshooting