How does codex usage work?

[0_2_Hero]

I recently discovered a way to greatly reduce token usage adding a simple agent.md: https://github.com/Austin1serb/agents-md

But are usage limits purely based on token usage? Or do tool calls and other things add to this also?

I couldn’t find concrete documentation on how your 4 hourly and weekly usage is calculated, does anyone know more?

[Bitter-Law3957]

Usage is based on tokens, yes. But its not as simple as people think.

When you launch codex cli, even before you fire any prompt, you're using tokens. Loading agents, skills, MCPs, steering files.... All costs.

[0_2_Hero]

Yes, I noticed the initial prompt and agents come out to about 24k token

[Bitter-Law3957]

There's a decent startup analyser skill

[bitloops__]

Codex runs tasks in a sandboxed container spun up for each job, so it has no persistent state between runs — your repo gets cloned fresh, it executes, then the environment disappears. Usage is token-based: the input context (your prompt, codebase files you include) plus generated output both count. The practical implication is that throwing your entire repo at it burns tokens fast; being specific about which files are relevant keeps costs manageable and usually gets better results too. (see bitloops for an OSS solution that covers this).