From 1608565c808c9136bdc6930a356649bd9824cc69 Mon Sep 17 00:00:00 2001
From: Spoon <212802214+spoons-and-mirrors@users.noreply.github.com>
Date: Fri, 13 Feb 2026 05:52:17 +0100
Subject: [PATCH] feat(hook): add tool.definition hook for plugins to modify
 tool description and parameters (#4956)

---
 packages/opencode/src/tool/registry.ts | 10 +++++++++-
 packages/plugin/src/index.ts           |  4 ++++
 2 files changed, 13 insertions(+), 1 deletion(-)

diff --git a/packages/opencode/src/tool/registry.ts b/packages/opencode/src/tool/registry.ts
index 5ed5a879b..9a06cb599 100644
--- a/packages/opencode/src/tool/registry.ts
+++ b/packages/opencode/src/tool/registry.ts
@@ -149,9 +149,17 @@ export namespace ToolRegistry {
         })
         .map(async (t) => {
           using _ = log.time(t.id)
+          const tool = await t.init({ agent })
+          const output = {
+            description: tool.description,
+            parameters: tool.parameters,
+          }
+          await Plugin.trigger("tool.definition", { toolID: t.id }, output)
           return {
             id: t.id,
-            ...(await t.init({ agent })),
+            ...tool,
+            description: output.description,
+            parameters: output.parameters,
           }
         }),
     )
diff --git a/packages/plugin/src/index.ts b/packages/plugin/src/index.ts
index 664f2c967..bd4ba5304 100644
--- a/packages/plugin/src/index.ts
+++ b/packages/plugin/src/index.ts
@@ -224,4 +224,8 @@ export interface Hooks {
     input: { sessionID: string; messageID: string; partID: string },
     output: { text: string },
   ) => Promise<void>
+  /**
+   * Modify tool definitions (description and parameters) sent to LLM
+   */
+  "tool.definition"?: (input: { toolID: string }, output: { description: string; parameters: any }) => Promise<void>
 }