From 8e7319e33025788f0dc505d3c684c847188b449b Mon Sep 17 00:00:00 2001
From: Rayan-and-beyond <263488867+Rayan-and-beyond@users.noreply.github.com>
Date: Tue, 15 Sep 2026 17:52:46 +0000
Subject: [PATCH] fix: estimate image_url tokens independently of URL length

---
 src/index.mjs       |  7 ++++++-
 test/basic.test.mjs | 13 +++++++++++++
 2 files changed, 19 insertions(+), 1 deletion(-)

diff --git a/src/index.mjs b/src/index.mjs
index ecb07e4..89c47ce 100644
--- a/src/index.mjs
+++ b/src/index.mjs
@@ -13,6 +13,10 @@ export function estimateTokens(text) {
   return Math.max(Math.ceil(chars / 4), Math.ceil(words * 1.3));
 }
 
+// Built-in flat estimate for image inputs. Image token accounting varies by model,
+// so keep this deterministic and independent of URL length.
+const IMAGE_TOKENS = 85;
+
 // Flatten any supported payload into text units: {role, kind, text}.
 // Supported: an array of messages, or { system, messages }.
 // Message content may be a string or an array of Anthropic-style blocks.
@@ -26,6 +30,7 @@ function blocksOf(content, role) {
       else if (b && b.type === "text") out.push({ role, kind: "text", text: b.text || "" });
       else if (b && b.type === "tool_use") out.push({ role, kind: "tool_use", text: JSON.stringify(b.input || {}) });
       else if (b && b.type === "tool_result") out.push({ role, kind: "tool_result", text: typeof b.content === "string" ? b.content : JSON.stringify(b.content ?? "") });
+      else if (b && b.type === "image_url") out.push({ role, kind: "image_url", text: "", fixedTokens: IMAGE_TOKENS });
       else out.push({ role, kind: (b && b.type) || "other", text: JSON.stringify(b) });
     }
     return out;
@@ -56,7 +61,7 @@ function units(payload) {
 
 // Report the token breakdown of a payload and where the tokens are going.
 export function analyzePayload(payload, { pricePerMTok = 3, counter = estimateTokens, top = 10 } = {}) {
-  const us = units(payload).map((u) => ({ ...u, tokens: counter(u.text) }));
+  const us = units(payload).map((u) => ({ ...u, tokens: u.fixedTokens ?? counter(u.text) }));
   const total = us.reduce((a, u) => a + u.tokens, 0);
   const byKind = {}, byRole = {};
   for (const u of us) {
diff --git a/test/basic.test.mjs b/test/basic.test.mjs
index 5c4158f..ac818d8 100644
--- a/test/basic.test.mjs
+++ b/test/basic.test.mjs
@@ -172,3 +172,16 @@ test("units rejects non-array payload.messages with TypeError", () => {
     { name: "TypeError", message: /payload\.messages must be an array/ },
   );
 });
+
+test("analyzePayload charges image_url blocks a flat documented estimate", () => {
+  const short = analyzePayload({ messages: [{ role: "user", content: [
+    { type: "image_url", image_url: { url: "https://example.com/a.png" } },
+  ] }] });
+  const long = analyzePayload({ messages: [{ role: "user", content: [
+    { type: "image_url", image_url: { url: `https://example.com/${"a".repeat(2000)}.png` } },
+  ] }] });
+
+  assert.equal(short.byKind.image_url, 85);
+  assert.equal(long.byKind.image_url, 85);
+  assert.equal(short.totalTokens, long.totalTokens);
+});