diff --git a/src/app/OutfitUrlsPage.js b/src/app/OutfitUrlsPage.js
index f5caaba..b339450 100644
--- a/src/app/OutfitUrlsPage.js
+++ b/src/app/OutfitUrlsPage.js
@@ -13,6 +13,12 @@ import {
   Input,
   InputGroup,
   InputRightElement,
+  Popover,
+  PopoverArrow,
+  PopoverBody,
+  PopoverContent,
+  PopoverTrigger,
+  Spinner,
   Tab,
   TabList,
   TabPanel,
@@ -25,9 +31,10 @@ import {
   VStack,
 } from "@chakra-ui/react";
 
-import { Delay, Heading1, Heading2 } from "./util";
+import { Delay, ErrorMessage, Heading1, Heading2 } from "./util";
 import HangerSpinner from "./components/HangerSpinner";
 import { gql, useQuery } from "@apollo/client";
+import { CheckIcon, WarningIcon } from "@chakra-ui/icons";
 
 function OutfitUrlsPage() {
   return (
@@ -253,9 +260,44 @@ function SingleImageConverter() {
 function BulkImageConverter() {
   const [inputHtml, setInputHtml] = React.useState("");
 
-  const outputHtml = inputHtml
-    ? "<!-- TODO: Not implemented yet! -->\n" + inputHtml
-    : "";
+  const parsedUrls = parseManyS3OutfitUrlsFromHtml(inputHtml);
+  const outfitIds = parsedUrls.map((pu) => pu.outfitId);
+
+  // TODO: Do this query in batches for large pages?
+  const { loading, error, data } = useQuery(
+    gql`
+      query OutfitUrlsBulkImageConverter($outfitIds: [ID!]!) {
+        outfits(ids: $outfitIds) {
+          id
+          # Rather than send requests for different sizes separately, I'm just
+          # requesting them all and having the client choose, to simplify the
+          # query. gzip should compress it very efficiently!
+          imageUrl600: imageUrl(size: SIZE_600)
+          imageUrl300: imageUrl(size: SIZE_300)
+          imageUrl150: imageUrl(size: SIZE_150)
+        }
+      }
+    `,
+    {
+      variables: { outfitIds },
+      skip: outfitIds.length === 0,
+      onError: (e) => console.error(e),
+    }
+  );
+
+  const { outputHtml, numReplacements, replacementErrors } = React.useMemo(
+    () =>
+      inputHtml && data?.outfits
+        ? replaceS3OutfitUrlsInHtml(inputHtml, data.outfits)
+        : { outputHtml: "", numReplacements: 0, replacementErrors: [] },
+    [inputHtml, data?.outfits]
+  );
+
+  React.useEffect(() => {
+    for (const replacementError of replacementErrors) {
+      console.error("Error replacing outfit URLs in HTML:", replacementError);
+    }
+  }, [replacementErrors]);
 
   const { onCopy, hasCopied } = useClipboard(outputHtml);
 
@@ -283,42 +325,164 @@ function BulkImageConverter() {
         />
       </FormControl>
       <FormControl gridArea="output">
-        <Flex alignItems="center" marginBottom="2">
-          <FormLabel fontSize="sm" margin="0">
-            Then, use this new HTML for your page instead:
-          </FormLabel>
-          <Box width="2" />
-          {outputHtml && (
-            <Button size="xs" onClick={onCopy}>
-              <Grid templateAreas="the-area">
-                <Box gridArea="the-area">{hasCopied ? "Copied!" : "Copy"}</Box>
-                {/* This invisible "Copied!" enforces a min size for the button
-                 * content, so that the button never changes size. */}
-                <Box gridArea="the-area" aria-hidden visibility="hidden">
-                  Copied!
-                </Box>
-              </Grid>
-            </Button>
-          )}
-        </Flex>
-        <Textarea
-          isReadOnly
-          fontFamily="monospace"
-          fontSize="xs"
-          placeholder={`<table> <!-- Example output, your new HTML will appear here! -->
+        <Grid
+          templateAreas={{
+            base: `
+              "header"
+              "textarea"
+              "status"
+            `,
+            md: `
+              "header status"
+              "textarea textarea"
+            `,
+          }}
+          alignItems="center"
+          rowGap="2"
+        >
+          <Flex gridArea="header" alignItems="center">
+            <FormLabel fontSize="sm" margin="0">
+              Then, use this new HTML for your page instead:
+            </FormLabel>
+            <Box width="2" flex={{ base: "1 0 auto", sm: "0 0 auto" }} />
+            {outputHtml && (
+              <Button size="xs" onClick={onCopy}>
+                <Grid templateAreas="the-area">
+                  <Box gridArea="the-area">
+                    {hasCopied ? "Copied!" : "Copy"}
+                  </Box>
+                  {/* This invisible "Copied!" enforces a min size for the button
+                   * content, so that the button never changes size. */}
+                  <Box gridArea="the-area" aria-hidden visibility="hidden">
+                    Copied!
+                  </Box>
+                </Grid>
+              </Button>
+            )}
+          </Flex>
+          <Textarea
+            gridArea="textarea"
+            isReadOnly
+            fontFamily="monospace"
+            fontSize="xs"
+            placeholder={`<table> <!-- Example output, your new HTML will appear here! -->
   <tr>
     <td><img src="https://impress-outfit-images.openneo.net/outfits/123456700/v/1234/600.png"></td>
     <td><img src="https://impress-outfit-images.openneo.net/outfits/123456701/v/5678/600.png"></td>
     <td><img src="https://impress-outfit-images.openneo.net/outfits/123456702/v/9012/600.png"></td>
     ...`}
-          value={outputHtml}
-        />
+            value={outputHtml}
+          />
+          <Box gridArea="status" textAlign="right" justifySelf="end">
+            {loading ? (
+              <Flex alignItems="center" opacity="0.8">
+                <Spinner size="xs" marginRight="1.5" />
+                <Box fontSize="sm">
+                  Found {outfitIds.length} outfit images, converting…
+                </Box>
+              </Flex>
+            ) : error ? (
+              <ErrorMessage fontSize="sm">
+                Error loading outfits. Try again?
+              </ErrorMessage>
+            ) : inputHtml && !outputHtml && outfitIds.length === 0 ? (
+              <Popover trigger="hover">
+                <PopoverTrigger>
+                  <Flex
+                    as={ErrorMessage}
+                    alignItems="center"
+                    fontSize="sm"
+                    tabIndex="0"
+                    borderRadius="md"
+                    paddingX="2"
+                    marginRight="-2"
+                    _focus={{ outline: "0", boxShadow: "outline" }}
+                  >
+                    <WarningIcon marginRight="1.5" />
+                    <Box>No outfit image URLs found</Box>
+                  </Flex>
+                </PopoverTrigger>
+                <PopoverContent>
+                  <PopoverArrow />
+                  <PopoverBody>
+                    <Box fontSize="xs" textAlign="center">
+                      <b>Make sure they're in the right format:</b>
+                      <br />
+                      https://openneo-uploads.s3.amazonaws.com/outfits/123/456/789/preview.png
+                      <br />
+                      <br />
+                      <b>
+                        If they're already in the new format, then you're
+                        already done!
+                      </b>{" "}
+                      The new format is:
+                      <br />
+                      https://impress-outfit-images.openneo.net/outfits/123456789/v/1020304050/600.png
+                    </Box>
+                  </PopoverBody>
+                </PopoverContent>
+              </Popover>
+            ) : outputHtml && replacementErrors.length > 0 ? (
+              <Popover trigger="hover">
+                <PopoverTrigger>
+                  <Flex
+                    as={
+                      replacementErrors.length > numReplacements
+                        ? ErrorMessage
+                        : undefined
+                    }
+                    alignItems="center"
+                    fontSize="sm"
+                    tabIndex="0"
+                    borderRadius="md"
+                    paddingX="2"
+                    marginRight="-2"
+                    _focus={{ outline: "0", boxShadow: "outline" }}
+                  >
+                    <WarningIcon marginRight="1.5" />
+                    <Box>
+                      Converted {numReplacements} outfit images, with{" "}
+                      {replacementErrors.length} errors
+                    </Box>
+                  </Flex>
+                </PopoverTrigger>
+                <PopoverContent width="50ch">
+                  <PopoverArrow />
+                  <PopoverBody>
+                    <Box fontSize="xs" textAlign="center">
+                      Errors are unusual at this point in the process. Sorry
+                      about this!
+                      <br />
+                      Email me at{" "}
+                      <a href="mailto:matchu@openneo.net">
+                        matchu@openneo.net
+                      </a>{" "}
+                      and I'll try to help!
+                      <br />
+                      We've left the {replacementErrors.length} erroring images
+                      unchanged for now.
+                    </Box>
+                  </PopoverBody>
+                </PopoverContent>
+              </Popover>
+            ) : outputHtml ? (
+              <Flex alignItems="center" fontSize="sm" opacity="0.8">
+                <CheckIcon marginRight="1.5" />
+                <Box>Converted {numReplacements} outfit images!</Box>
+              </Flex>
+            ) : null}
+          </Box>
+        </Grid>
       </FormControl>
     </Grid>
   );
 }
 
-const S3_OUTFIT_URL_PATTERN = /^https?:\/\/openneo-uploads\.s3\.amazonaws\.com\/outfits\/([0-9]{3})\/([0-9]{3})\/([0-9]{3})\/(preview|medium_preview|small_preview)\.png$/;
+// These patterns have the same content, but different boundary conditions and
+// flags. EXACT is for checking a single string for an exact match, GLOBAL is
+// for finding multiple matches in large text.
+const S3_OUTFIT_URL_EXACT_PATTERN = /^https?:\/\/openneo-uploads\.s3\.amazonaws\.com\/outfits\/([0-9]{3})\/([0-9]{3})\/([0-9]{3})\/(preview|medium_preview|small_preview)\.png$/;
+const S3_OUTFIT_URL_GLOBAL_PATTERN = /https?:\/\/openneo-uploads\.s3\.amazonaws\.com\/outfits\/([0-9]{3})\/([0-9]{3})\/([0-9]{3})\/(preview|medium_preview|small_preview)\.png/g;
 const S3_FILENAMES_TO_SIZES = {
   preview: 600,
   medium_preview: 300,
@@ -330,7 +494,7 @@ function parseS3OutfitUrl(url) {
     return null;
   }
 
-  const match = S3_OUTFIT_URL_PATTERN.exec(url);
+  const match = S3_OUTFIT_URL_EXACT_PATTERN.exec(url);
   if (!match) {
     throw new Error(
       `This URL didn't match the expected pattern. Make sure it's formatted like this: https://openneo-uploads.s3.amazonaws.com/outfits/123/456/789/preview.png`
@@ -345,4 +509,56 @@ function parseS3OutfitUrl(url) {
   return { outfitId, size };
 }
 
+function parseManyS3OutfitUrlsFromHtml(html) {
+  const matches = html.match(S3_OUTFIT_URL_GLOBAL_PATTERN) || [];
+  return matches.map(parseS3OutfitUrl);
+}
+
+function replaceS3OutfitUrlsInHtml(html, outfits) {
+  const outfitsById = new Map();
+  for (const outfit of outfits) {
+    if (!outfit) {
+      continue;
+    }
+    outfitsById.set(outfit.id, outfit);
+  }
+
+  // Use the `replace` method to scan the HTML for matches, which will run this
+  // function on each match to decide what to replace it with. We'll count
+  // successes and log failures along the way!
+  let numReplacements = 0;
+  const replacementErrors = [];
+  const outputHtml = html.replace(S3_OUTFIT_URL_GLOBAL_PATTERN, (match) => {
+    let newUrl;
+    try {
+      const { outfitId, size } = parseS3OutfitUrl(match);
+      const outfit = outfitsById.get(outfitId);
+      if (!outfit) {
+        throw new Error(`could not find outfit ${outfitId}`);
+      }
+
+      const sizeKey = `imageUrl` + size;
+
+      if (!(sizeKey in outfit)) {
+        throw new Error(
+          `outfit ${outfitId} has no image key ${sizeKey}: ${JSON.stringify(
+            outfit
+          )}`
+        );
+      }
+
+      newUrl = outfit[sizeKey];
+    } catch (e) {
+      e.message += ` (${match})`; // help us understand which URL failed!
+      replacementErrors.push(e);
+      return match;
+    }
+
+    numReplacements++;
+    return newUrl;
+  });
+
+  return { outputHtml, numReplacements, replacementErrors };
+}
+
 export default OutfitUrlsPage;
diff --git a/src/server/types/Outfit.js b/src/server/types/Outfit.js
index 31a4acd..d0d95c2 100644
--- a/src/server/types/Outfit.js
+++ b/src/server/types/Outfit.js
@@ -31,6 +31,7 @@ const typeDefs = gql`
 
   extend type Query {
     outfit(id: ID!): Outfit
+    outfits(ids: [ID!]!): [Outfit]!
   }
 
   extend type Mutation {
@@ -137,6 +138,11 @@ const resolvers = {
 
       return { id };
     },
+
+    outfits: async (_, { ids }, { outfitLoader }) => {
+      const outfits = await outfitLoader.loadMany(ids);
+      return outfits.map((outfit) => (outfit ? { id: outfit.id } : null));
+    },
   },
 
   Mutation: {