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SessionCost

Step 0

Step 0 is everything the agent sends before your first message: its own instructions, the tools it can use, your rules files (such as CLAUDE.md or AGENTS.md), skills, and MCP servers.

It matters because it is sent again with every call in the chat. A Step 0 of 30,000 tokens in a chat with 200 calls is 6 million tokens sent, before counting a word you typed.

Read it

Section titled “Read it”

Step 0 is the first tile on the path. Tap it, then What is in Step 0. One bar splits Step 0 into its parts, then lists every tool, used or never used, so you can see what you pay for and never use.

Step 0: 32k sent on every call, split into tool definitions, the system prompt and more; ten connected tools never used

Make it smaller

Section titled “Make it smaller”

How to save in Step 0 lists the fixes for this chat. The usual ones:

  • Turn off MCP servers you do not use in this project. Each one adds its tools to Step 0.
  • Keep rules files short. Move rarely needed detail into a separate file the agent reads only when it needs it.
  • Remove skills and plugins you no longer use.

Run /sessioncost again after the change: Step 0 should shrink in the next chat.