Add mcp search tool, lazy mcp load, reduce mcp tool occupying a lot of context

Resolved 💬 7 comments Opened Jan 15, 2026 by saidelike Closed Aug 5, 2026

💡 Likely answer: A maintainer (etraut-openai, contributor) responded on this thread — see the highlighted reply below.

What feature would you like to see?

When MCP tool descriptions exceed 10% of the context window, they are automatically deferred and discovered via the MCPSearch tool instead of being loaded upfront. This reduces context usage for users with many MCP tools configured.

References:

high level description: https://x.com/i/status/2011523109871108570
tool search specification: https://platform.claude.com/docs/en/agents-and-tools/tool-use/tool-search-tool
original Claude Code issue: https://github.com/anthropics/claude-code/issues/7336

Related issues:

https://github.com/openai/codex/issues/2335

Additional information

_No response_

View original on GitHub ↗

7 Comments

Eriz1818 · 6 months ago

I implemented optional / lazy loading of MCP servers in my fork, xCodex (xcodex), and shipped it in v0.3.5.

xCodex: https://github.com/Eriz1818/xCodex
Release notes: https://github.com/Eriz1818/xCodex/blob/main/docs/xcodex/releases/0.3.5.md
Docs: https://github.com/Eriz1818/xCodex/blob/main/docs/xcodex/lazy-mcp-loading.md

What it adds:

Global + per-server MCP “startup_mode”: eager (default) | lazy | manual
lazy: don’t start servers at session start; start on first tool/resource use
manual: never auto-start; load explicitly
In-session command: /mcp load <name> (plus /mcp status + /mcp retry ...)
CLI one-run override: xcodex --mcp-startup-mode lazy (or eager/manual)

This keeps startup fast for sessions that don’t use MCP, while still making it easy to opt-in when you do. AND saving on context!

saidelike · 6 months ago

I implemented optional / lazy loading of MCP servers in my fork, xCodex (xcodex), and shipped it in v0.3.5. xCodex: https://github.com/Eriz1818/xCodex Release notes: https://github.com/Eriz1818/xCodex/blob/main/docs/xcodex/releases/0.3.5.md Docs: https://github.com/Eriz1818/xCodex/blob/main/docs/xcodex/lazy-mcp-loading.md What it adds: Global + per-server MCP “startup_mode”: eager (default) | lazy | manual lazy: don’t start servers at session start; start on first tool/resource use manual: never auto-start; load explicitly In-session command: /mcp load <name> (plus /mcp status + /mcp retry ...) * CLI one-run override: xcodex --mcp-startup-mode lazy (or eager/manual) This keeps startup fast for sessions that don’t use MCP, while still making it easy to opt-in when you do. AND saving on context!

wow nice. Would you be able to do a PR for the official codex repo? Seems very useful :)

tokezooo · 6 months ago

This is very much needed

yifanyifan897645 · 5 months ago

While waiting for native lazy loading support, you can at least identify which MCP servers are the worst offenders using mcp-checkup:

npx mcp-checkup

It analyzes your setup, measures token cost per server/tool, and grades them A-F. Users with many MCP servers often discover 2-3 servers account for 80% of context overhead — disabling just those gives you most of the benefit of lazy loading without client-side changes.

Zero config, just npx and go.

taotao365s · 2 months ago

Necmttn · 2 months ago

Lazy MCP loading probably needs four states, not only eager versus lazy: configured, manifest-known, started, and invoked.

Tool search can operate over manifest-known servers without paying startup cost, then start a server only when a selected tool needs execution. The metric to watch is also two numbers: manifest tokens loaded into the prompt and first-use latency after tool selection. That prevents the fix from trading context overhead for opaque stalls on the first real MCP call.

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_Generated with ax._

etraut-openai contributor · 23 days ago

tool_search avoids eagerly loading every MCP tool.