diff --git a/src/agents/types.ts b/src/agents/types.ts
index 7484d0e..5586039 100644
--- a/src/agents/types.ts
+++ b/src/agents/types.ts
@@ -21,6 +21,8 @@ export type OverridableAgentName =
 
 export type AgentName = BuiltinAgentName
 
-export type AgentOverrideConfig = Partial<AgentConfig>
+export type AgentOverrideConfig = Partial<AgentConfig> & {
+  prompt_append?: string
+}
 
 export type AgentOverrides = Partial<Record<OverridableAgentName, AgentOverrideConfig>>
diff --git a/src/agents/utils.ts b/src/agents/utils.ts
index 568f269..1f24238 100644
--- a/src/agents/utils.ts
+++ b/src/agents/utils.ts
@@ -66,7 +66,14 @@ function mergeAgentConfig(
   base: AgentConfig,
   override: AgentOverrideConfig
 ): AgentConfig {
-  return deepMerge(base, override as Partial<AgentConfig>)
+  const { prompt_append, ...rest } = override
+  const merged = deepMerge(base, rest as Partial<AgentConfig>)
+
+  if (prompt_append && merged.prompt) {
+    merged.prompt = merged.prompt + "\n" + prompt_append
+  }
+
+  return merged
 }
 
 export function createBuiltinAgents(
diff --git a/src/config/schema.ts b/src/config/schema.ts
index 125e88d..a50bcff 100644
--- a/src/config/schema.ts
+++ b/src/config/schema.ts
@@ -70,6 +70,7 @@ export const AgentOverrideConfigSchema = z.object({
   temperature: z.number().min(0).max(2).optional(),
   top_p: z.number().min(0).max(1).optional(),
   prompt: z.string().optional(),
+  prompt_append: z.string().optional(),
   tools: z.record(z.string(), z.boolean()).optional(),
   disable: z.boolean().optional(),
   description: z.string().optional(),