diff --git a/.changeset/use-append-text-file.md b/.changeset/use-append-text-file.md
new file mode 100644
index 00000000..170c2f70
--- /dev/null
+++ b/.changeset/use-append-text-file.md
@@ -0,0 +1,10 @@
+---
+"create-expert": patch
+---
+
+Use appendTextFile instead of editTextFile in ecosystem-builder
+
+The ecosystem-builder instruction incorrectly told the LLM to use
+editTextFile for appending content. editTextFile is a search-and-replace
+tool, not an append tool. Changed to use appendTextFile which is the
+correct tool for adding content to the end of a file.
diff --git a/apps/create-expert/src/lib/create-expert-toml.ts b/apps/create-expert/src/lib/create-expert-toml.ts
index c9fd903a..d34368f0 100644
--- a/apps/create-expert/src/lib/create-expert-toml.ts
+++ b/apps/create-expert/src/lib/create-expert-toml.ts
@@ -87,13 +87,10 @@ Generate not just a single Expert, but an **ecosystem** of experts that ensures
 4. **Doctor Expert**: Only if external dependencies exist - diagnoses and fixes issues
 
 ## Output
-Use editTextFile to APPEND the Expert ecosystem to the existing perstack.toml.
+Use appendTextFile to add the Expert ecosystem to perstack.toml.
+First read the file to understand the existing structure, then append your Expert sections.
 Do NOT use writeTextFile - it would overwrite the entire file.
-
-## How to Append
-1. First, read perstack.toml to understand the existing structure
-2. Use editTextFile to add your Expert sections at the END of the file
-3. Do NOT modify model, runtime, or provider settings - they already exist
+Do NOT modify model, runtime, or provider settings - they already exist.
 
 ## Ecosystem Generation Strategy