diff --git a/CHANGELOG.md b/CHANGELOG.md
index 93a2d4b..e7edf67 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -24,6 +24,7 @@ _If you are upgrading from 1.x: please see [Migrating from 1.x](MIGRATING.md)._
 - Reduce every tool response with no fact lost: `apexlog_list_slow_operations` by 33% ([#86], [#108]) and `apexlog_execute_anonymous` by 30% ([#86], [#109]). `apexlog_get_summary` costs 16% more on a log that uses its limits, for the two tables it gained ([#62])
 - **Breaking:** move to the MCP TypeScript SDK v2 packages, so the server speaks the 2026-07-28 protocol revision. Clients on the 2025 revisions keep working through the SDK's compatibility layer ([#103])
 - Reduce the standing cost of having the server connected by 29%: `apexlog_execute_anonymous` by 50%, `apexlog_list_limit_risks` by 28% and `apexlog_get_summary` by 5% ([#87], [#108], [#103]). `apexlog_list_slow_operations` costs 28% more, for the five parameters that select what it ranks ([#108])
+- Encode responses with TOON v4. No response changed: v4 removes key folding and path expansion, and this server used neither ([#121])
 - Parse a log once rather than once per tool, cached by path, inode, size, modification time and change time, so a summary followed by a deeper tool no longer reads and parses the file again. The parse is dropped after five minutes unused, so a large log is not held for the life of the session ([#88])
 
 ### Added
@@ -69,3 +70,4 @@ _If you are upgrading from 1.x: please see [Migrating from 1.x](MIGRATING.md)._
 [#108]: https://github.com/certinia/debug-log-analyzer-mcp/issues/108
 [#103]: https://github.com/certinia/debug-log-analyzer-mcp/issues/103
 [#109]: https://github.com/certinia/debug-log-analyzer-mcp/issues/109
+[#121]: https://github.com/certinia/debug-log-analyzer-mcp/issues/121
diff --git a/DEVELOPING.md b/DEVELOPING.md
index 33763db..b38ad4e 100644
--- a/DEVELOPING.md
+++ b/DEVELOPING.md
@@ -222,6 +222,11 @@ one-liners.
   ".gitignore" sentence it replaced was ~15, and it answers the question either way.
 - **Say in the tool description what is omitted and when.** Currently that is one sentence per tool,
   because there is one omission per tool.
+- **Encode with the TOON defaults.** Measured, none of the alternatives pay:
+  - `indentSize: 1` — saves 2.4%, but `decode` rejects it without a matching `indentSize`.
+  - keyed tabular (`[n:]`) — costs one character per row, `,` becoming `: `.
+  - `delimiter` tab or pipe — 2 tokens on a 9,365-token response. Quoting comes from `:` in a name.
+  - nested field groups — nothing left to fold; every table is already flat.
 
 ### The gate
 
diff --git a/package.json b/package.json
index 6e8f930..96e8cf1 100644
--- a/package.json
+++ b/package.json
@@ -56,7 +56,7 @@
     "@modelcontextprotocol/client": "^2.0.0",
     "@modelcontextprotocol/server": "^2.0.0",
     "@salesforce/core": "^8.32.3",
-    "@toon-format/toon": "^2.3.0",
+    "@toon-format/toon": "^4.1.1",
     "zod": "^4.4.3"
   },
   "devDependencies": {
diff --git a/pnpm-lock.yaml b/pnpm-lock.yaml
index f4c25e6..212f201 100644
--- a/pnpm-lock.yaml
+++ b/pnpm-lock.yaml
@@ -18,8 +18,8 @@ importers:
         specifier: ^8.32.3
         version: 8.32.6
       '@toon-format/toon':
-        specifier: ^2.3.0
-        version: 2.3.0
+        specifier: ^4.1.1
+        version: 4.1.1
       zod:
         specifier: ^4.4.3
         version: 4.4.3
@@ -637,8 +637,8 @@ packages:
   '@swc/types@0.1.28':
     resolution: {integrity: sha512-V6Mnml8v09QALx6K0elJ7o9K/MkVDtW3t6L+7Ou/JcWtb3xwId2AH4FeOceySd2JaO87IMw4+6vSZxLm34LPbw==}
 
-  '@toon-format/toon@2.3.0':
-    resolution: {integrity: sha512-/Ew9etdRQKVMnm9fDaCG0JjyAOK/O7T0M97oum1aW4W+UR8ZhVVPBanIV7oWgHBiGlnVxV9M55PWQCHofDV07w==}
+  '@toon-format/toon@4.1.1':
+    resolution: {integrity: sha512-SGCkS7IjVpwRmGPgnY8ENKpAf0EdAnZDOQkvFW0d2cgOpdn9FEFl7sTgryESyypXrWr0YajHGpwsAUX4zw9ZvA==}
 
   '@tsconfig/node10@1.0.12':
     resolution: {integrity: sha512-UCYBaeFvM11aU2y3YPZ//O5Rhj+xKyzy7mvcIoAjASbigy8mHMryP5cK7dgjlz2hWxh1g5pLw084E0a/wlUSFQ==}
@@ -3285,7 +3285,7 @@ snapshots:
     dependencies:
       '@swc/counter': 0.1.3
 
-  '@toon-format/toon@2.3.0': {}
+  '@toon-format/toon@4.1.1': {}
 
   '@tsconfig/node10@1.0.12':
     optional: true