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MCP Shrink Proxy

contextcrumb-shrink wraps another MCP stdio server and compresses verbose catalog descriptions before the agent sees them.

It is for a different problem than contextcrumb-mcp:

  • contextcrumb-mcp gives the agent compression tools.
  • contextcrumb-shrink compresses another server's tool, prompt, resource, and resource-template descriptions.

Tool calls, tool results, names, schemas, and resource contents are forwarded unchanged.

Basic Usage​

contextcrumb-shrink -- upstream-mcp-server --flag value

The upstream command is everything after --.

Service Mode​

For a lighter proxy, start a warm service and use it from the shrink proxy:

contextcrumb service start
contextcrumb-shrink --mode service -- upstream-mcp-server

Fields​

By default, the proxy compresses only description fields.

Compress extra catalog fields:

contextcrumb-shrink --fields description,title -- upstream-mcp-server

Environment variable equivalent:

CONTEXTCRUMB_SHRINK_FIELDS=description,title contextcrumb-shrink -- upstream-mcp-server

Compression Budget​

The default shrink proxy target keep ratio is 0.5.

Tune it:

contextcrumb-shrink --target-keep-ratio 0.4 -- upstream-mcp-server

Environment variable:

CONTEXTCRUMB_SHRINK_TARGET_KEEP_RATIO=0.4 contextcrumb-shrink -- upstream-mcp-server

Debugging​

contextcrumb-shrink --debug -- upstream-mcp-server

Or:

CONTEXTCRUMB_SHRINK_DEBUG=1 contextcrumb-shrink -- upstream-mcp-server

Protected Text​

The proxy preserves protected spans outside model input, including:

  • Fenced code blocks
  • Inline code
  • URLs
  • Windows and Unix-like paths
  • Function calls
  • Dotted identifiers
  • Snake case and uppercase identifiers
  • Version strings
  • Small JSON-like objects

This keeps catalog descriptions shorter without breaking important handles or names.