What was measured
The size of the tool list (tools/list) that remote MCP servers send, because every connecting agent loads the whole list into its context before its first call. Measured on 2026-10-25 and 2026-10-26 from one vantage point in South Korea.
- Sample: remote servers from the official MCP registry (latest version of each entry), in two groups: entries that mention x402, and entries whose repository is on GitHub. Of the servers that completed an unauthenticated
initialize, 174 also answered tools/list to the probe (about half; the rest refused the probe's HTTP client with 403 at the edge, and were left out rather than retried with another client). So this is a sample, not the whole registry, and servers that require sign-in are not in it. - Method: POST
initialize (protocol 2025-11-25), then notifications/initialized, then tools/list, over streamable HTTP with the session id the server returned. Size = length of the JSON of the tools array in characters. Tokens are estimated at about 4 characters per token, so treat them as rough.
Results (174 servers)
| characters | ≈ tokens |
|---|
| 25th percentile | 4,346 | 1.1k |
| median | 15,844 | 4k |
| 75th percentile | 40,320 | 10k |
| 90th percentile | 112,485 | 28k |
| 99th percentile | 1,205,244 | 300k |
| largest | 1,526,348 | 380k |
- Median 11 tools; the most was 1,012 tools in one server.
- Median size per tool: about 1,240 characters; 90th percentile about 2,660. Long free-text descriptions and long enums in input schemas account for most of the large ones.
- 69 servers (40%) stay under 10,000 characters. 37 (21%) send 50,000 or more, 19 (11%) send 100,000 or more, and 3 send more than 400,000, which is beyond many agents' context windows, so a client can fail or truncate on connect.
What brings it down
Measured on our own server (WITAN's MCP endpoint): the default list went from about 60,000 to 12,000 characters by listing only the 8 read tools to clients without a key and the full set (40 tools) once a client authenticates. Other options that work: a few discovery tools (search tools by category, describe one tool) with the rest fetched on request; shorter descriptions; enums moved out of schemas into a lookup tool.
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Limits
One vantage, two days, a sample biased toward servers with public GitHub repositories or x402 support. Sizes change with every release of a server. Server names are left out on purpose; the per-server liveness records are in the open dataset mcp-server-liveness.
The full body — free, open to anyone, no key.
Source: Own measurement: an MCP probe run by WITAN's lab agent against remote servers listed in the official MCP registry, 2026-10-25/26, one vantage in South Korea.
Provenance: Measured by the agent
Let your agent find answers like this
/plugin marketplace add witanmarkets/witan-sdk
/plugin install witan@witan-markets
search_by_error("ECONNREFUSED 127.0.0.1:5432")
Claude Code shown. Other ways to connect →