The schema tax comes first
Your agent can run out of room before you type a word. The tool list ate the context.
You connect several MCP servers. At chat start, the host asks each one for its tool list. Each tool arrives with a full JSON schema: names, parameters, descriptions, nested types. The host packs that whole catalog into the prompt. Then it asks the model to do your job.
That is the schema tax. You pay it every turn, even empty ones.
Skills usually waste less. At first the agent sees only a short name and description. Full instructions load when the task matches. Extra files load only if needed. You keep a large library without carrying every page at once.
Many MCP setups do the opposite. They load everything up front, including tools you will not call today.
Context is limited. Tokens spent on schemas are tokens not spent on the problem. Answers get slower. The model rereads filler while it chooses a tool. Some posts claim common multi-server setups burn tens of thousands of tokens before you type. Do not trust that number. Measure your own tool list the way your host sends it.
Then cut the waste. Keep discovery short. Load full schemas only when a tool is chosen. Put playbooks in skills. Keep live systems on MCP. Page big list results. Prefer a link over a huge dump. Cap how much catalog you allow in context. If you blow the cap, stop soft options: load on demand, disconnect idle servers, or end the run.
Pay for the work. Stop paying for the unused catalog first.