tool(mcp registry): debloat context of mcp descriptions

packages/opencode/src/cli/cmd/tui/routes/session/index.tsx

@@ -40,6 +40,7 @@ import type { EditTool } from "@/tool/edit"
 import type { PatchTool } from "@/tool/patch"
 import type { WebFetchTool } from "@/tool/webfetch"
 import type { TaskTool } from "@/tool/task"
+import type { MCPRegistryTool } from "@/tool/mcp-registry"
 import { useKeyboard, useRenderer, useTerminalDimensions, type BoxProps, type JSX } from "@opentui/solid"
 import { useSDK } from "@tui/context/sdk"
 import { useCommandDialog } from "@tui/component/dialog-command"
@@ -1224,7 +1225,7 @@ type ToolProps<T extends Tool.Info> = {
 }
 function GenericTool(props: ToolProps<any>) {
   return (
-    <ToolTitle icon="⚙" fallback="Writing command..." when={true}>
+    <ToolTitle icon="▣" fallback="Writing command..." when={true}>
       {props.tool} {input(props.input)}
     </ToolTitle>
   )
@@ -1621,6 +1622,19 @@ ToolRegistry.register<typeof TodoWriteTool>({
   },
 })
 
+ToolRegistry.register<typeof MCPRegistryTool>({
+  name: "mcp_registry",
+  container: "inline",
+  render(props) {
+    const activate = props.input.activate
+    return (
+      <ToolTitle icon="→" fallback="Activating MCP tools..." when={activate?.length}>
+        MCP Registry activate [{activate?.join(", ")}]
+      </ToolTitle>
+    )
+  },
+})
+
 function normalizePath(input?: string) {
   if (!input) return ""
   if (path.isAbsolute(input)) {

packages/opencode/src/config/config.ts

@@ -642,6 +642,10 @@ export namespace Config {
           chatMaxRetries: z.number().optional().describe("Number of retries for chat completions on failure"),
           disable_paste_summary: z.boolean().optional(),
           batch_tool: z.boolean().optional().describe("Enable the batch tool"),
+          mcp_registry: z
+            .boolean()
+            .optional()
+            .describe("Hide MCP tools behind a registry tool that the model can query"),
         })
         .optional(),
     })

packages/opencode/src/session/prompt.ts

@@ -33,6 +33,7 @@ import { mergeDeep, pipe } from "remeda"
 import { ToolRegistry } from "../tool/registry"
 import { Wildcard } from "../util/wildcard"
 import { MCP } from "../mcp"
+import { getActivatedTools, decrementActivatedTools } from "../tool/mcp-registry"
 import { LSP } from "../lsp"
 import { ReadTool } from "../tool/read"
 import { ListTool } from "../tool/ls"
@@ -41,6 +42,7 @@ import { ulid } from "ulid"
 import { spawn } from "child_process"
 import { Command } from "../command"
 import { $, fileURLToPath } from "bun"
+import { Config } from "../config/config"
 import { ConfigMarkdown } from "../config/markdown"
 import { SessionSummary } from "./summary"
 import { NamedError } from "@/util/error"
@@ -196,6 +198,7 @@ export namespace SessionPrompt {
 
     const message = await createUserMessage(input)
     await Session.touch(input.sessionID)
+    decrementActivatedTools(input.sessionID)
 
     if (input.noReply === true) {
       return message
@@ -468,7 +471,7 @@ export namespace SessionPrompt {
         agent,
         system: lastUser.system,
       })
-      const tools = await resolveTools({
+      const { tools, hiddenTools } = await resolveTools({
         agent,
         sessionID,
         model: lastUser.model,
@@ -544,7 +547,7 @@ export namespace SessionPrompt {
           },
           // set to 0, we handle loop
           maxRetries: 0,
-          activeTools: Object.keys(tools).filter((x) => x !== "invalid"),
+          activeTools: Object.keys(tools).filter((x) => x !== "invalid" && !hiddenTools.has(x)),
           maxOutputTokens: ProviderTransform.maxOutputTokens(
             model.providerID,
             params.options,
@@ -651,6 +654,7 @@ export namespace SessionPrompt {
     processor: SessionProcessor.Info
   }) {
     const tools: Record<string, AITool> = {}
+    const hiddenTools = new Set<string>()
     const enabledTools = pipe(
       input.agent.tools,
       mergeDeep(await ToolRegistry.enabled(input.model.providerID, input.model.modelID, input.agent)),
@@ -724,6 +728,9 @@ export namespace SessionPrompt {
       })
     }
 
+    const config = await Config.get()
+    const mcpRegistryEnabled = config.experimental?.mcp_registry === true
+    const activatedTools = mcpRegistryEnabled ? getActivatedTools(input.sessionID) : undefined
     for (const [key, item] of Object.entries(await MCP.tools())) {
       if (Wildcard.all(key, enabledTools) === false) continue
       const execute = item.execute
@@ -786,8 +793,11 @@ export namespace SessionPrompt {
         }
       }
       tools[key] = item
+      if (activatedTools && !activatedTools.has(key)) {
+        hiddenTools.add(key)
+      }
     }
-    return tools
+    return { tools, hiddenTools }
   }
 
   async function createUserMessage(input: PromptInput) {

packages/opencode/src/tool/mcp-registry.ts

@@ -0,0 +1,80 @@
+import z from "zod"
+import { Tool } from "./tool"
+import { MCP } from "../mcp"
+import DESCRIPTION from "./mcp-registry.txt"
+
+// Track which MCP tools are activated per session (after being described)
+// Key: sessionID, Value: Map of toolName -> remaining turns
+const activatedTools = new Map<string, Map<string, number>>()
+const ACTIVATION_TURNS = 3
+
+export function getActivatedTools(sessionID: string): Set<string> {
+  const session = activatedTools.get(sessionID)
+  if (!session) return new Set()
+  return new Set(session.keys())
+}
+
+export function decrementActivatedTools(sessionID: string) {
+  const session = activatedTools.get(sessionID)
+  if (!session) return
+  for (const [tool, turns] of session) {
+    if (turns <= 1) {
+      session.delete(tool)
+    } else {
+      session.set(tool, turns - 1)
+    }
+  }
+  if (session.size === 0) {
+    activatedTools.delete(sessionID)
+  }
+}
+
+function activateTool(sessionID: string, toolName: string) {
+  let session = activatedTools.get(sessionID)
+  if (!session) {
+    session = new Map()
+    activatedTools.set(sessionID, session)
+  }
+  session.set(toolName, ACTIVATION_TURNS)
+}
+
+export const MCPRegistryTool = Tool.define("mcp_registry", async () => {
+  const mcpTools = await MCP.tools()
+  const names = Object.keys(mcpTools).map((n) => n.replaceAll("-", "_"))
+  const description = `${DESCRIPTION}\n\nAvailable MCP tools: [${names.join(", ")}]`
+
+  return {
+    description,
+    parameters: z.object({
+      activate: z.array(z.string()).describe("Array of exact tool names to activate."),
+    }),
+    async execute(params, ctx) {
+      const currentTools = await MCP.tools()
+      const results: string[] = []
+      const activated: string[] = []
+
+      for (const name of params.activate) {
+        const tool = currentTools[name]
+        if (!tool) {
+          results.push(`Tool "${name}" not found`)
+          continue
+        }
+        activateTool(ctx.sessionID, name)
+        activated.push(name)
+      }
+
+      if (activated.length > 0) {
+        results.push(
+          `Activated ${activated.length} tool(s): ${activated.join(", ")}`,
+          "These tools are now temporarily available in your environment.",
+        )
+      }
+
+      return {
+        title: activated.length ? `Activated ${activated.length} tools` : "No tools activated",
+        output: results.join("\n"),
+        metadata: {},
+      }
+    },
+  }
+})

packages/opencode/src/tool/mcp-registry.txt

@@ -0,0 +1,8 @@
+Activate MCP tools from connected servers.
+
+To use an MCP tool, you must first activate it using this tool. Once activated, the tool becomes available in this environment for a few turns.
+
+Usage:
+- Review the available MCP tools listed below
+- Call this tool with the exact tool name(s) you want to activate
+- Once activated, the tools and their descriptions are available in context so you can use them directly

packages/opencode/src/tool/registry.ts

@@ -10,6 +10,7 @@ import { TodoWriteTool, TodoReadTool } from "./todo"
 import { WebFetchTool } from "./webfetch"
 import { WriteTool } from "./write"
 import { InvalidTool } from "./invalid"
+import { MCPRegistryTool } from "./mcp-registry"
 import type { Agent } from "../agent/agent"
 import { Tool } from "./tool"
 import { Instance } from "../project/instance"
@@ -98,6 +99,7 @@ export namespace ToolRegistry {
       TodoWriteTool,
       TodoReadTool,
       ...(config.experimental?.batch_tool === true ? [BatchTool] : []),
+      ...(config.experimental?.mcp_registry === true ? [MCPRegistryTool] : []),
       ...(Flag.OPENCODE_EXPERIMENTAL_EXA ? [WebSearchTool, CodeSearchTool] : []),
       ...custom,
     ]

packages/plugin/package.json

@@ -24,4 +24,4 @@
     "typescript": "catalog:",
     "@typescript/native-preview": "catalog:"
   }
-}
+}

packages/sdk/js/package.json

@@ -26,4 +26,4 @@
   "publishConfig": {
     "directory": "dist"
   }
-}
+}

packages/sdk/js/src/gen/types.gen.ts

@@ -1218,6 +1218,10 @@ export type Config = {
      * Enable the batch tool
      */
     batch_tool?: boolean
+    /**
+     * Hide MCP tools behind a registry tool that the model can query
+     */
+    mcp_registry?: boolean
   }
 }