fix(mcp): let the read tool carry a request body

call_read_operation declared no body, so the six read operations that post their filter as JSON — searchKnowledge, queryRows, queryRowsCount, searchTableRows, getSelector, and listSelector — could not be called at all. The dispatcher already sends a body for any non-GET operation that declares one and refuses a body for operations that do not, so both call tools now share one input schema.

Author: waleedlatif1

apps/sim/lib/api/mcp/route-handler.test.ts

@@ -46,6 +46,19 @@ function rpc(
   })
 }
 
+interface ListedTool {
+  annotations: Record<string, boolean>
+  inputSchema: { properties: Record<string, unknown> }
+}
+
+async function listTools(): Promise<Record<string, ListedTool>> {
+  const response = await handlers.POST(rpc({ method: 'tools/list' }), undefined)
+  const { result } = await response.json()
+  return Object.fromEntries(
+    result.tools.map((tool: ListedTool & { name: string }) => [tool.name, tool])
+  )
+}
+
 async function callTool(
   name: string,
   args: Record<string, unknown>,
@@ -112,22 +125,27 @@ describe('Sim MCP admission', () => {
 
 describe('Sim MCP tools', () => {
   it('lists four tools with reads and writes annotated apart', async () => {
-    const response = await handlers.POST(rpc({ method: 'tools/list' }), undefined)
-    const { result } = await response.json()
-    const tools = Object.fromEntries(
-      result.tools.map((tool: { name: string; annotations: Record<string, boolean> }) => [
-        tool.name,
-        tool.annotations,
-      ])
-    )
+    const tools = await listTools()
     expect(Object.keys(tools).sort()).toEqual([
       'call_read_operation',
       'call_write_operation',
       'describe_operation',
       'search_operations',
     ])
-    expect(tools.call_read_operation.readOnlyHint).toBe(true)
-    expect(tools.call_write_operation.destructiveHint).toBe(true)
+    expect(tools.call_read_operation.annotations.readOnlyHint).toBe(true)
+    expect(tools.call_write_operation.annotations.destructiveHint).toBe(true)
+  })
+
+  /**
+   * A read is not always a GET: searchKnowledge, queryRows, and searchTableRows
+   * among others post their filter as JSON, so a read tool whose schema has no
+   * body cannot call them at all.
+   */
+  it('lets both call tools carry a request body', async () => {
+    const tools = await listTools()
+    for (const name of ['call_read_operation', 'call_write_operation']) {
+      expect(tools[name].inputSchema.properties, name).toHaveProperty('body')
+    }
   })
 
   it('finds operations by keyword', async () => {

apps/sim/lib/api/mcp/server.ts

@@ -33,21 +33,6 @@ const operationName = z
   .max(128)
   .describe('Operation name from search_operations, e.g. "listTables".')
 
-const operationArgs = {
-  params: z
-    .record(z.string(), z.string())
-    .optional()
-    .describe('Path parameters by name, e.g. { "tableId": "..." }.'),
-  query: z
-    .record(z.string(), z.union([z.string(), z.number(), z.boolean()]))
-    .optional()
-    .describe('Query-string parameters by name.'),
-  headers: z
-    .record(z.string(), z.string())
-    .optional()
-    .describe('Request headers the operation declares, such as upload-token.'),
-}
-
 const searchInput = z
   .object({
     query: z
@@ -65,12 +50,22 @@ const searchInput = z
 
 const describeInput = z.object({ operation: operationName }).strict()
 
-const readInput = z.object({ operation: operationName, ...operationArgs }).strict()
-
-const writeInput = z
+/** Shared because a read is not always a GET: searching and querying post their filter as JSON. */
+const callInput = z
   .object({
     operation: operationName,
-    ...operationArgs,
+    params: z
+      .record(z.string(), z.string())
+      .optional()
+      .describe('Path parameters by name, e.g. { "tableId": "..." }.'),
+    query: z
+      .record(z.string(), z.union([z.string(), z.number(), z.boolean()]))
+      .optional()
+      .describe('Query-string parameters by name.'),
+    headers: z
+      .record(z.string(), z.string())
+      .optional()
+      .describe('Request headers the operation declares, such as upload-token.'),
     body: z.unknown().optional().describe('JSON request body, as describe_operation specifies.'),
   })
   .strict()
@@ -142,7 +137,7 @@ export function createSimMcpServer(context: Omit<McpDispatchContext, 'signal'>):
       title: 'Read from Sim',
       description:
         'Run a Sim API operation that only reads, such as listWorkspaces, listTables, queryRows, or getWorkflowRun. search_operations says which tool runs each operation.',
-      inputSchema: readInput,
+      inputSchema: callInput,
       annotations: { readOnlyHint: true, idempotentHint: true, openWorldHint: false },
     },
     async (input, extra) => call('read', input, extra.signal)
@@ -154,7 +149,7 @@ export function createSimMcpServer(context: Omit<McpDispatchContext, 'signal'>):
       title: 'Change Sim',
       description:
         'Run a Sim API operation that creates, changes, runs, or deletes something, such as createTable, executeWorkflow, or deleteFile.',
-      inputSchema: writeInput,
+      inputSchema: callInput,
       annotations: {
         readOnlyHint: false,
         destructiveHint: true,