angular/angular-cli · error · Error

Proxy configuration file ${proxyPath} contains parse errors:

Error message

Proxy configuration file ${proxyPath} contains parse errors:

What it means

For a `.json` proxy config, the dev-server config parses the file with the JSON scanner and collects parse errors. This error is thrown when the proxy JSON is syntactically invalid; the message lists each error with its [line, column] and a parse error code. It prevents serving with a malformed proxy configuration.

Source

Thrown at packages/angular_devkit/build_angular/src/tools/webpack/configs/dev-server.ts:185

  }

  let proxyConfiguration;

  switch (extname(proxyPath)) {
    case '.json': {
      const content = await fsPromises.readFile(proxyPath, 'utf-8');

      const { parse, printParseErrorCode } = await import('jsonc-parser');
      const parseErrors: import('jsonc-parser').ParseError[] = [];
      proxyConfiguration = parse(content, parseErrors, { allowTrailingComma: true });

      if (parseErrors.length > 0) {
        let errorMessage = `Proxy configuration file ${proxyPath} contains parse errors:`;
        for (const parseError of parseErrors) {
          const { line, column } = getJsonErrorLineColumn(parseError.offset, content);
          errorMessage += `\n[${line}, ${column}] ${printParseErrorCode(parseError.error)}`;
        }
        throw new Error(errorMessage);
      }

      break;
    }
    default: {
      try {
        proxyConfiguration = await import(proxyPath);
      } catch (e) {
        assertIsError(e);
        if (e.code !== 'ERR_REQUIRE_ASYNC_MODULE') {
          throw e;
        }

        proxyConfiguration = await loadEsmModule<{ default: unknown }>(pathToFileURL(proxyPath));
      }

      break;
    }

View on GitHub (pinned to bb72145f9a)

Solutions

1. Fix the JSON syntax at the reported [line, column] from the error message (remove trailing commas, comments, single quotes).
2. Validate the file with `node -e "JSON.parse(require('fs').readFileSync('proxy.conf.json'))"` or an editor JSON linter.
3. If you need comments/JS logic, rename the file to proxy.conf.js and export a config object instead of keeping it as .json.
4. Regenerate a clean proxy.conf.json (e.g. `ng g config` style examples) and re-add your proxy entries.

Example fix

// before: proxy.conf.json
{ "/api": { "target": "http://localhost:3000", "secure": false, }, }
// after
{
  "/api": { "target": "http://localhost:3000", "secure": false }
}

import * as fs from 'fs';
const content = fs.readFileSync('proxy.conf.json', 'utf8');
try { JSON.parse(content); } catch (e) {
  throw new Error(`proxy.conf.json is invalid JSON: ${e.message}`);
}

When it happens

Trigger: `ng serve` with a `proxyConfig` ending in `.json` whose content fails JSON parsing (trailing commas, comments, single quotes, missing braces) — `parseErrors.length > 0` in `addProxyConfig`.

Common situations: Hand-editing proxy.conf.json and leaving a trailing comma or comment; copy-pasting a `proxy.conf.js` (JavaScript syntax) into a `.json` file; BOM or stray characters; merge-conflict markers left in the file.

Understand the failure class

• Parsing and encoding errors: unexpected token, malformed input — why parsers reject input and how to find the real culprit.

Related errors

• Proxy configuration file ${proxyPath} does not exist.
• Header "forwarded" proto parameter must be either "http" or
• Header "x-forwarded-port" must be a numeric value.
• Header "x-forwarded-proto" must be either "http" or "https".
• Header "x-forwarded-prefix" is invalid. It must start with a

AI-assisted analysis of angular/angular-cli@bb72145f9a (2026-08-30). Data as JSON: /api/errors/cd483156dbb381b9. Report an issue: GitHub.