diff --git a/cli/src/guidance/core.ts b/cli/src/guidance/core.ts
index c43ff8c6c0..100bea6e53 100644
--- a/cli/src/guidance/core.ts
+++ b/cli/src/guidance/core.ts
@@ -74,7 +74,7 @@ You are a helpful assistant that can help with Windmill scripts, flows, apps, an
 
 ## Script Writing Guide
 
-You MUST use the \`write-script-<language>\` skill to write or modify scripts in the language specified by the user. Use bun by default.
+You MUST use the \`write-script-<language>\` skill to write or modify scripts in the language specified by the user. Use bun by default. For TypeScript, always prefer bun (\`write-script-bun\`) over deno unless the script specifically requires the Deno runtime.
 For Workflow-as-Code scripts, use the \`write-workflow-as-code\` skill.
 
 ## Flow Writing Guide
diff --git a/cli/src/guidance/skills.gen.ts b/cli/src/guidance/skills.gen.ts
index 69e4338d22..cc51106162 100644
--- a/cli/src/guidance/skills.gen.ts
+++ b/cli/src/guidance/skills.gen.ts
@@ -10,10 +10,10 @@ export const SKILLS: SkillMetadata[] = [
   { name: "write-script-ansible", description: "MUST use when writing Ansible playbooks.", languageKey: "ansible" },
   { name: "write-script-bash", description: "MUST use when writing Bash scripts.", languageKey: "bash" },
   { name: "write-script-bigquery", description: "MUST use when writing BigQuery queries.", languageKey: "bigquery" },
-  { name: "write-script-bun", description: "MUST use when writing Bun/TypeScript scripts.", languageKey: "bun" },
+  { name: "write-script-bun", description: "MUST use when writing TypeScript scripts. Bun is the default and preferred TypeScript runtime — pick it for TypeScript unless the script specifically needs Deno.", languageKey: "bun" },
   { name: "write-script-bunnative", description: "MUST use when writing Bun Native scripts. The script must start with //native to run on the native worker.", languageKey: "bunnative" },
   { name: "write-script-csharp", description: "MUST use when writing C# scripts.", languageKey: "csharp" },
-  { name: "write-script-deno", description: "MUST use when writing Deno/TypeScript scripts.", languageKey: "deno" },
+  { name: "write-script-deno", description: "Use ONLY when a TypeScript script specifically requires the Deno runtime (Deno stdlib or deno.land URL imports). For all other TypeScript, use write-script-bun instead.", languageKey: "deno" },
   { name: "write-script-duckdb", description: "MUST use when writing DuckDB queries.", languageKey: "duckdb" },
   { name: "write-script-go", description: "MUST use when writing Go scripts.", languageKey: "go" },
   { name: "write-script-graphql", description: "MUST use when writing GraphQL queries.", languageKey: "graphql" },
@@ -374,7 +374,7 @@ being buffered, bypassing the 10000-row return cap.
 `,
   "write-script-bun": `---
 name: write-script-bun
-description: MUST use when writing Bun/TypeScript scripts.
+description: MUST use when writing TypeScript scripts. Bun is the default and preferred TypeScript runtime — pick it for TypeScript unless the script specifically needs Deno.
 ---
 
 ## CLI Commands
@@ -424,7 +424,7 @@ Use \`wmill resource-type list --schema\` to discover available resource types.
 
 # TypeScript (Bun)
 
-Bun runtime with full npm ecosystem and fastest execution.
+Bun runtime with full npm ecosystem and fastest execution. **Bun is the default and preferred TypeScript runtime** — choose it for any TypeScript script unless there is a major reason to use Deno for that specific use-case.
 
 ## Structure
 
@@ -1994,7 +1994,7 @@ public class Script
 `,
   "write-script-deno": `---
 name: write-script-deno
-description: MUST use when writing Deno/TypeScript scripts.
+description: Use ONLY when a TypeScript script specifically requires the Deno runtime (Deno stdlib or deno.land URL imports). For all other TypeScript, use write-script-bun instead.
 ---
 
 ## CLI Commands
@@ -2046,6 +2046,8 @@ Use \`wmill resource-type list --schema\` to discover available resource types.
 
 Deno runtime with npm support via \`npm:\` prefix and native Deno libraries.
 
+**Prefer Bun (\`write-script-bun\`) for TypeScript.** Only use Deno when the script specifically requires the Deno runtime — Deno's standard library or \`deno.land\` URL imports that have no npm equivalent. For all other TypeScript, use Bun instead.
+
 ## Structure
 
 Export a single **async** function called \`main\`:
diff --git a/system_prompts/auto-generated/prompts.ts b/system_prompts/auto-generated/prompts.ts
index fb2e40e6ec..5670c53fcd 100644
--- a/system_prompts/auto-generated/prompts.ts
+++ b/system_prompts/auto-generated/prompts.ts
@@ -3729,7 +3729,7 @@ being buffered, bypassing the 10000-row return cap.
 
 export const LANG_BUN = `# TypeScript (Bun)
 
-Bun runtime with full npm ecosystem and fastest execution.
+Bun runtime with full npm ecosystem and fastest execution. **Bun is the default and preferred TypeScript runtime** — choose it for any TypeScript script unless there is a major reason to use Deno for that specific use-case.
 
 ## Structure
 
@@ -4016,6 +4016,8 @@ export const LANG_DENO = `# TypeScript (Deno)
 
 Deno runtime with npm support via \`npm:\` prefix and native Deno libraries.
 
+**Prefer Bun (\`write-script-bun\`) for TypeScript.** Only use Deno when the script specifically requires the Deno runtime — Deno's standard library or \`deno.land\` URL imports that have no npm equivalent. For all other TypeScript, use Bun instead.
+
 ## Structure
 
 Export a single **async** function called \`main\`:
diff --git a/system_prompts/auto-generated/script.md b/system_prompts/auto-generated/script.md
index 9d393d2c7f..f5a6fd99ba 100644
--- a/system_prompts/auto-generated/script.md
+++ b/system_prompts/auto-generated/script.md
@@ -215,7 +215,7 @@ being buffered, bypassing the 10000-row return cap.
 
 # TypeScript (Bun)
 
-Bun runtime with full npm ecosystem and fastest execution.
+Bun runtime with full npm ecosystem and fastest execution. **Bun is the default and preferred TypeScript runtime** — choose it for any TypeScript script unless there is a major reason to use Deno for that specific use-case.
 
 ## Structure
 
@@ -502,6 +502,8 @@ public class Script
 
 Deno runtime with npm support via `npm:` prefix and native Deno libraries.
 
+**Prefer Bun (`write-script-bun`) for TypeScript.** Only use Deno when the script specifically requires the Deno runtime — Deno's standard library or `deno.land` URL imports that have no npm equivalent. For all other TypeScript, use Bun instead.
+
 ## Structure
 
 Export a single **async** function called `main`:
diff --git a/system_prompts/auto-generated/skills/write-script-bun/SKILL.md b/system_prompts/auto-generated/skills/write-script-bun/SKILL.md
index 44cccc7ba8..21aafa55d0 100644
--- a/system_prompts/auto-generated/skills/write-script-bun/SKILL.md
+++ b/system_prompts/auto-generated/skills/write-script-bun/SKILL.md
@@ -1,6 +1,6 @@
 ---
 name: write-script-bun
-description: MUST use when writing Bun/TypeScript scripts.
+description: MUST use when writing TypeScript scripts. Bun is the default and preferred TypeScript runtime — pick it for TypeScript unless the script specifically needs Deno.
 ---
 
 ## CLI Commands
@@ -50,7 +50,7 @@ Use `wmill resource-type list --schema` to discover available resource types.
 
 # TypeScript (Bun)
 
-Bun runtime with full npm ecosystem and fastest execution.
+Bun runtime with full npm ecosystem and fastest execution. **Bun is the default and preferred TypeScript runtime** — choose it for any TypeScript script unless there is a major reason to use Deno for that specific use-case.
 
 ## Structure
 
diff --git a/system_prompts/auto-generated/skills/write-script-deno/SKILL.md b/system_prompts/auto-generated/skills/write-script-deno/SKILL.md
index ea2bfd4421..55c7bf7155 100644
--- a/system_prompts/auto-generated/skills/write-script-deno/SKILL.md
+++ b/system_prompts/auto-generated/skills/write-script-deno/SKILL.md
@@ -1,6 +1,6 @@
 ---
 name: write-script-deno
-description: MUST use when writing Deno/TypeScript scripts.
+description: Use ONLY when a TypeScript script specifically requires the Deno runtime (Deno stdlib or deno.land URL imports). For all other TypeScript, use write-script-bun instead.
 ---
 
 ## CLI Commands
@@ -52,6 +52,8 @@ Use `wmill resource-type list --schema` to discover available resource types.
 
 Deno runtime with npm support via `npm:` prefix and native Deno libraries.
 
+**Prefer Bun (`write-script-bun`) for TypeScript.** Only use Deno when the script specifically requires the Deno runtime — Deno's standard library or `deno.land` URL imports that have no npm equivalent. For all other TypeScript, use Bun instead.
+
 ## Structure
 
 Export a single **async** function called `main`:
diff --git a/system_prompts/languages/bun.md b/system_prompts/languages/bun.md
index c505b6cf97..22aeb2fb74 100644
--- a/system_prompts/languages/bun.md
+++ b/system_prompts/languages/bun.md
@@ -1,6 +1,6 @@
 # TypeScript (Bun)
 
-Bun runtime with full npm ecosystem and fastest execution.
+Bun runtime with full npm ecosystem and fastest execution. **Bun is the default and preferred TypeScript runtime** — choose it for any TypeScript script unless there is a major reason to use Deno for that specific use-case.
 
 ## Structure
 
diff --git a/system_prompts/languages/deno.md b/system_prompts/languages/deno.md
index c84e5e772a..fddd08efb2 100644
--- a/system_prompts/languages/deno.md
+++ b/system_prompts/languages/deno.md
@@ -2,6 +2,8 @@
 
 Deno runtime with npm support via `npm:` prefix and native Deno libraries.
 
+**Prefer Bun (`write-script-bun`) for TypeScript.** Only use Deno when the script specifically requires the Deno runtime — Deno's standard library or `deno.land` URL imports that have no npm equivalent. For all other TypeScript, use Bun instead.
+
 ## Structure
 
 Export a single **async** function called `main`:
diff --git a/system_prompts/utils.py b/system_prompts/utils.py
index 9666b6cf0c..e2fa77d3b6 100644
--- a/system_prompts/utils.py
+++ b/system_prompts/utils.py
@@ -87,13 +87,13 @@ CLI_EXCLUDED_FIELDS = [
 LANGUAGE_METADATA = {
     'bun': {
         'name': 'TypeScript (Bun)',
-        'description': 'MUST use when writing Bun/TypeScript scripts.',
-        'use_cases': 'TypeScript automation, npm packages, data processing, API integrations'
+        'description': 'MUST use when writing TypeScript scripts. Bun is the default and preferred TypeScript runtime — pick it for TypeScript unless the script specifically needs Deno.',
+        'use_cases': 'TypeScript automation, npm packages, data processing, API integrations — the default choice for TypeScript'
     },
     'deno': {
         'name': 'TypeScript (Deno)',
-        'description': 'MUST use when writing Deno/TypeScript scripts.',
-        'use_cases': 'TypeScript with Deno stdlib, secure sandboxed execution'
+        'description': 'Use ONLY when a TypeScript script specifically requires the Deno runtime (Deno stdlib or deno.land URL imports). For all other TypeScript, use write-script-bun instead.',
+        'use_cases': 'TypeScript that specifically needs the Deno runtime (Deno stdlib or deno.land imports); prefer Bun otherwise'
     },
     # 'nativets' is intentionally omitted: it is a legacy duplicate of
     # 'bunnative' (a Bun script with a leading //native marker). No