io.github.mrfentmen/jsonschema-mcp

jsonschema-mcp

Is the io.github.mrfentmen/jsonschema-mcp MCP server down? No. It answered initialize and tools/list in the probe of 2026-10-29.

Validate JSON against a JSON Schema offline, with a clear list of every structural error

alive probed 2026-11-15 · unchanged since 2026-10-29

3tools

616tokens in Claude Opus 5.5

0.3 %of Claude's 200k window

0.2×the median server

258 msto initialize

6 msto list tools

Run it: npx -y @mrfentmen/jsonschema-mcp@1.0.1 (stdio, probed in a container with the network off)
Host: npmjs.com
Reports itself as: jsonschema-mcp 1.0.0
Capabilities: tools
Instructions: none
Of a 1M window: <0.1 % of a 1M context window
Count: 616 tokens in Claude Opus 5.5, exact, measured 2026-10-29. With the Claude Code prefix mcp__…__ on each tool name: 658. The o200k_base estimate is 332. Counted again when the tool definitions change. Method.
Repository: https://github.com/mrfentmen/awesome-servers
Registry: active, updated 2026-10-28 · registry entry

Most expensive tools

The Claude column scales the o200k estimate of each tool by this server's ratio of exact to estimate, 1.86×.

Tool	≈ Claude tokens	o200k estimate	Share of this server
validate_json	250	135	41 %
describe_schema	210	113	34 %
example_from_schema	156	84	25 %

Other registry entries on npmjs.com, the ones next to this name; all of them.

Servers that mention jsonschema or structural or validate.

The result of the latest probe, the tool count and the token cost. The feed has an entry for every probe that changed them.

Stops answering, comes back, tool set or cost changes. One confirmation mail first, a stop link in every mail.