diff --git a/docs/backlog/P1/B-0170.1-semantic-equivalence-drift-checker.md b/docs/backlog/P1/B-0170.1-semantic-equivalence-drift-checker.md
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+---
+id: B-0170.1
+priority: P1
+status: open
+title: "Substrate-claim-checker - semantic-equivalence-drift checker"
+created: 2026-05-28
+last_updated: 2026-05-28
+parent: B-0170
+depends_on: []
+classification: buildable-now
+decomposition: atomic
+owners: [lior]
+type: tooling
+---
+
+# B-0170.1 — Semantic-equivalence-drift checker
+
+This task implements the "semantic-equivalence-drift" checker, as specified in the parent task B-0170.
+
+## Scope
+
+This checker is responsible for detecting claims of semantic equivalence between commands in documentation and verifying them. For example, if a document states that `ll` is an alias for `ls -l`, this checker should be able to validate that claim.
+
+### V0.1 (This task)
+
+The initial version of this tool will only *detect* claims of semantic equivalence. It will scan markdown files for patterns like:
+
+- `<code>...</code> is equivalent to <code>...</code>`
+- `<code>...</code> is an alias for <code>...</code>`
+- `<code>...</code> is the same as <code>...</code>`
+
+It will then report the file and line number where these claims are made. Verification of the claims is out of scope for this initial version.
+
+## Acceptance Criteria
+
+- A new script `tools/substrate-claim-checker/check-semantic-equivalence.ts` is created.
+- The script can be run from the command line.
+- The script scans markdown files for claims of semantic equivalence.
+- The script outputs a list of found claims with their location.
diff --git a/tools/substrate-claim-checker/check-semantic-equivalence.ts b/tools/substrate-claim-checker/check-semantic-equivalence.ts
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+#!/usr/bin/env bun
+// check-semantic-equivalence.ts -- finds claims of semantic equivalence in markdown files.
+// Part of B-0170.1.
+
+import fs from 'fs';
+import path from 'path';
+
+const CLAIM_REGEX = /`([^`]+)`\s+(is equivalent to|is an alias for|is the same as)\s+`([^`]+)`/gi;
+// `upstreams` excludes references/upstreams/ — 85+ full clones of external
+// projects; walking it takes minutes and returns mostly noise (per
+// .claude/rules/references-upstreams-not-our-code-search-excludes.md).
+const IGNORE_DIRS = ['node_modules', '.git', '.vscode', '.idea', 'dist', 'build', 'upstreams'];
+const INCLUDE_EXTS = ['.md', '.mdx'];
+
+interface Match {
+  file: string;
+  line: number;
+  claim: string;
+}
+
+function searchInFile(filePath: string): Match[] {
+  const matches: Match[] = [];
+  if (!INCLUDE_EXTS.some(ext => filePath.endsWith(ext))) {
+    return matches;
+  }
+
+  try {
+    const content = fs.readFileSync(filePath, 'utf-8');
+    const lines = content.split('\n');
+
+    for (let i = 0; i < lines.length; i++) {
+      const line = lines[i];
+      let match;
+      while ((match = CLAIM_REGEX.exec(line)) !== null) {
+        matches.push({
+          file: filePath,
+          line: i + 1,
+          claim: match[0],
+        });
+      }
+    }
+  } catch (error) {
+    // Surface read failures to stderr so silently-skipped files are visible
+    // (a swallowed read produces a false negative — "no claims" when the file
+    // was actually unreadable).
+    console.error(`warn: could not read ${filePath}: ${(error as Error).message}`);
+  }
+
+  return matches;
+}
+
+function searchInDirectory(dirPath: string): Match[] {
+  let allMatches: Match[] = [];
+  const entries = fs.readdirSync(dirPath, { withFileTypes: true });
+
+  for (const entry of entries) {
+    const fullPath = path.join(dirPath, entry.name);
+    if (IGNORE_DIRS.includes(entry.name)) {
+      continue;
+    }
+
+    if (entry.isDirectory()) {
+      allMatches = allMatches.concat(searchInDirectory(fullPath));
+    } else if (entry.isFile()) {
+      allMatches = allMatches.concat(searchInFile(fullPath));
+    }
+  }
+
+  return allMatches;
+}
+
+function main() {
+  const searchDir = process.argv[2] || process.cwd();
+  console.log(`Searching for semantic equivalence claims in ${searchDir}...\n`);
+
+  const allMatches = searchInDirectory(searchDir);
+
+  if (allMatches.length === 0) {
+    console.log('No semantic equivalence claims found.');
+    return;
+  }
+
+  console.log(`Found ${allMatches.length} potential claims:\n`);
+  for (const match of allMatches) {
+    console.log(`- ${match.file}:${match.line}`);
+    console.log(`  > ${match.claim}`);
+  }
+}
+
+if (import.meta.main) {
+  main();
+}