# X_MCP_EFFECT_UNDECLARED

## Means

an MCP tool on a meta-split surface declares no effect

## Typical cause

defineAppMcp({ surface: 'meta-split' }) groups an action whose mcp block names no effect, so no dispatcher can be picked for it

## Fix

`add mcp: { expose: true, effect: 'write' } (or 'delete' for an archive, a send or a spend) to the action, or tools: { name: { effect } } for a hand-written tool`

[MCP and AI](/error-codes#mcp-and-ai)