mcptokens 0.1.2

172 tokens in your agent's harness. One MCP tool that counts the tool-definition cost of any other MCP server.

mcptokens

172 tokens in your agent's harness. One tool, inspect, that counts the tool-definition cost of any other MCP server before you enable it.

pip install mcptokens

---

Why

When your agent enables a new MCP server, its tools enter the agent's context on every turn. The cost compounds fast. mcptokens lets the agent ask is this server cheap enough? before flipping the switch.

How

Add mcptokens to your agent's MCP config (Claude Code, Pi, OpenCode, Codex, ...). The agent gains one tool:

{
  "name": "inspect",
  "description": "Count tool-def tokens of any MCP server. Pass argv [...]",
  "inputSchema": {
    "properties": {
      "command":  {"type": "array",  "items": {"type": "string"}},
      "encoding": {"type": "string", "enum": ["cl100k_base","o200k_base"], "default": "cl100k_base"},
      "timeout":  {"type": "number", "default": 15, "minimum": 1, "maximum": 60}
    },
    "required": ["command"]
  }
}

Then the agent calls:

inspect(command=["hound"])                      # 1023 wire tokens, 8 tools
inspect(command=["python", "-m", "my_server"])  # ...

The agent decides whether to enable the candidate server based on the answer.

The numbers

Self-cost on wire	172 tokens of cl100k_base
Tools exposed	1, named inspect
Cross-platform	Linux, macOS, Windows
Python	3.11+
Imports	tiktoken, mcp
Source	5 files, ~700 LOC
Tests	31 passing in under 10 seconds

Install

pip install mcptokens

Add mcptokens to your agent's mcpServers / mcp_servers. Done.

CLI (debug surface)

mcptokens hound                       # human table
mcptokens --json hound                # pipeline-friendly JSON
mcptokens --timeout 30 python -m srv  # custom spawn
mcptokens serve                       # run as an MCP server
mcptokens --version                   # 0.1.0

Flag	Default	Purpose
--encoding	cl100k_base	cl100k_base or o200k_base
--timeout	15	Per-server timeout in seconds (1 to 60)
--json	false	Output JSON instead of the table

Why it's cheap

One server, one tool, tight description, minimal schema. The shipped tool definition tokenizes to 172 tokens. A small tool list is the product.

Tests

python -m pytest tests/  # 31 passing in under 10 seconds

Engine tests cover JSON-RPC id-matching, null-safe shape coercion, timeouts, and end-to-end via mcp.ClientSession.

License

MIT. pip install mcptokens from the canonical PyPI index.