Nearly half of MCP server updates silently change what agents are told

A developer launched 152 versions of 23 popular npm MCP servers and found that 40 of 86 version-to-version updates (47%) altered the tool surface — names, descriptions, schemas or annotations. Parameter descriptions were rewritten 92 times, far more often than tools were added (12) or removed (4).

• 40 of 86 updates (47%) changed the MCP server tool surface
• 92 parameter descriptions rewritten vs 12 tools added and 4 removed
• One server changed its tool list 6 times in 6 releases, from 85 to 103 tools
• An independent researcher measured 48% across 96 releases on 9 servers