Know what you feed your agent.

efaimo is an open source CLI. It counts the tokens your MCP servers and Agent Skills add to every request, and checks them for quality and for the 2026-07-28 MCP spec.

npx efaimo weigh --client claude-code

Other clients: cursor, vscode, claude-desktop.
v0.6.0 on npm, Apache 2.0, Node 22+

1,759 dots · 16 tools · one MCP server

One dot per token. The bright ones are its heaviest tool, gzip-file-as-resource.

npx efaimo weigh "npx -y @modelcontextprotocol/server-everything" real run · 2026-11-02 
efaimo v0.6.0
weigh mcp  npx -y @modelcontextprotocol/server-everything
tools 16   resources 7   prompts 4

context cost of tool definitions (o200k tokens, estimated)
  raw JSON           2,424
  Claude-style       1,759   (~0.2% of a 1M window)
  OpenAI tools       1,772
  server instructions  831

heaviest tools (Claude-style)
   1. gzip-file-as-resource        243   desc 72 | schema 160
   2. get-header-params            177   desc 57 | schema 109
   3. trigger-log-messages         130   desc 93 | schema 26
   4. trigger-resource-update      126   desc 57 | schema 59
   5. trigger-list-changed         118   desc 53 | schema 54
   6. get-annotated-message        104   desc 14 | schema 78
   7. get-env                      103   desc 66 | schema 26
   8. toggle-simulated-logging      90   desc 51 | schema 26
      (+8 more)
      block framing                     85   (<functions> wrapper; per-tool lines + this = total)

note: token counts are estimates using the o200k_base tokenizer; hosts add fixed framing text on top (see docs/METHODOLOGY.md)

Output for the official MCP reference server, the one drawn above. What these numbers mean

Commands

No account, no service, no config file. It reads what you point it at and prints what it found.

  • efaimo weigh

    Counts the tokens a server or skill adds to every request.

  • efaimo check --mcp

    Grades an MCP server and lists what to change for the 2026-07-28 spec.

  • efaimo check --skill

    Grades a skill: frontmatter, size, trigger collisions, broken references.

  • efaimo test

    Runs a task with and without a skill and reports the difference. Experimental

  • efaimo mcp

    Lets your agent check and weigh skills itself, over MCP.

Every command with a real run ->

What it found

8 MCP servers, installed together

39,887

tokens of tool definitions across 117 tools, 4.0% of a 1M window before you type anything.

  1. @notionhq/notion-mcp-server 17,218 24 tools
  2. firecrawl-mcp 12,231 26 tools
  3. @playwright/mcp 3,981 25 tools
  4. server-everything 1,759 16 tools
  5. server-filesystem 1,743 14 tools
  6. @upstash/context7-mcp 1,074 2 tools
  7. server-memory 1,007 9 tools
  8. server-sequential-thinking 874 1 tool

Tokens, Claude-style. The bright row is the server in the run at the top of this page. A plausible set of servers, not a census.

How these were chosen ->

36 public Agent Skills

97%

grade A. The one below A is also the heaviest, at 18,419 tokens of instructions each time it fires.

Instruction tokens, one bar per skill, heaviest first.

Every skill, row by row ->

Measured with efaimo v0.6.0 · 2026-11-02

Questions

  • What is efaimo?

    An open source CLI, Apache 2.0, that measures what MCP (Model Context Protocol) servers and Agent Skills cost in context tokens and grades their quality. It is pronounced eh-fai-mo (Korean: 에파이모). efaimo ai makes it and runs this site.

  • How do I install it?

    Run npx efaimo with Node 22 or later, or pin it in a project with npm i -D efaimo. Version 0.6.0 is on npm, published with provenance from github.com/efaimo-ai/efaimo.

  • Does efaimo send data anywhere?

    No. The CLI talks only to the servers and files you point it at, plus, with your own key, the model API for efaimo test and Anthropic's count-tokens API for --anthropic. This site counts visits with a cookieless Cloudflare beacon and Google Analytics with every ads signal off; the privacy page lists what they see.

  • Where do the numbers on this site come from?

    From committed runs of efaimo dated 2026-11-02, and from command output printed exactly as it ran. Every figure is computed from those runs when the site is built, and the build checks that each one traces back to a run.

  • What changed in MCP on July 28?

    The 2026-07-28 MCP specification removes sessions and the initialize handshake, and calls the change breaking in its own words. Nothing broke that day: the same release sets a minimum twelve-month deprecation window. efaimo check --mcp lists what a server still has to change.

Try it on your own setup

npx efaimo weigh --client claude-code

Source on GitHub Package on npm How the numbers are made