Download (free)
The whole tool is one file, pac-tester.html. Nothing to install and no network access, so it works on locked-down work PCs and on machines with no internet connection.
The tool's screen is in Japanese. The key labels are below.
Test FindProxyForURL offline
- Many URLs at once: put one URL per line and get the return value for each (
DIRECT,PROXY host:port; …) in a table - All 14 standard helper functions
- Diff mode: evaluate an old and a new PAC against the same URLs and highlight only the URLs whose result changed
More features
- The host name is taken from each URL for you
- You set the DNS answers (a host-to-IP table), the value of
myIpAddress()and the date and time the script sees - Colour-coded results: each distinct return value gets a colour and a count; click one to filter.
alert()output, errors and timeouts show on the row they belong to. Export to CSV - The 14 helpers:
isInNet,shExpMatch,dnsDomainIs,weekdayRange,timeRangeand the rest (see the guide) - Infinite loops can't freeze it: each URL is cut off after 0.2 seconds
PAC file debugger: what the checks find
The checks parse the script (with acorn) without running it, and point to the line.
What the checks look for
The checks are approximate and will not catch every mistake.
- No
FindProxyForURL, a wrongly capitalised name, the wrong number of parameters, or two definitions - Full-width (CJK) spaces and punctuation, and zero-width spaces, pasted into code. An error in code, a warning inside strings, ignored in comments
- Unbalanced
( ) { } [ ]and unclosed quotes, with the line where they open and where they go wrong - Paths where the function can end without a
return, and return values in the wrong format (,instead of;,"PROXY"with no host, a port out of range) shExpMatchpatterns that can never match, such as".example.com"without*, a scheme in a host pattern, or a URL pattern missing its trailing/- Shadowed rules: an earlier
if (…) return …;whose pattern already covers a later one, so the later rule is never reached - Suspicious helper calls: a non-contiguous
isInNetmask,dnsDomainIswithout the leading dot, lower-caseweekdayRangedays,timeRange(22, 6)
How to use it
- Download pac-tester.html and double-click it
- Paste your PAC into the left-hand box, or drag and drop a .pac file onto the page
- List the URLs to test in the right-hand box, one per line. Results and check messages update as you type
| Label on screen | Meaning |
|---|---|
| PAC ファイル | PAC file (paste here) |
| テストする URL | URLs to test |
| 結果 | Results |
| 構文・ロジックのチェック | Syntax and logic checks |
| 評価の設定 | Evaluation settings (click to expand) |
| 差分モード | Diff mode |
Reading the Japanese screen (all labels)
| Label on screen | Meaning |
|---|---|
| 評価する | Evaluate now (Ctrl+Enter). Normally not needed: it re-evaluates 400 ms after you stop typing |
| 差分モード | Diff mode |
| 見本 | Load the sample PAC, URLs and settings |
| ライセンス | About this tool and the bundled library's license |
| PAC ファイル | PAC file (paste here) |
| 開く | Open a file |
| 旧 PAC（いまの版）／新 PAC（変更後） | Old PAC (current) / New PAC (changed), in diff mode |
| 旧を写す | Copy the old PAC into the new box |
| PAC と URL 一覧も、このブラウザに保存する | Also save the PAC and URL list in this browser (off by default) |
| 構文・ロジックのチェック | Syntax and logic checks. Click a message to jump to its line |
| エラー／注意／参考 | Error / Warning / Info |
| 問題は見つかりませんでした | No problems found |
| shExpMatch のパターン一覧 | List of every shExpMatch pattern in the file |
| テストする URL | URLs to test (one per line; lines starting with # are comments) |
| .txt を開く／.txt で保存 | Open / save the URL list as a .txt file |
| 評価の設定 | Evaluation settings (click to expand) |
| ホスト名と IP アドレスの対応表 | Host-to-IP table, used instead of DNS |
| myIpAddress() が返す IP アドレス | IP address returned by myIpAddress() |
| 評価に使う日時／いまの日時を使う | Date and time the script sees / use the current date and time |
| UTC との時差 | UTC offset |
| https の URL は、パスとクエリを除いて渡す | Strip the path and query from https URLs (on by default, as Chrome and Edge do) |
| 結果 | Results |
| URL・結果で絞り込み | Filter by URL or result |
| 変わった行だけ／エラー・注意だけ | Changed rows only (diff mode) / Errors and warnings only |
| CSV で保存 | Save as CSV |
| タイムアウト／エラー／変更 | Timeout / Error / Changed |
| undefined（戻り値なし） | undefined (the function returned nothing) |
| PAC に渡す URL | The URL actually passed to FindProxyForURL (shown when the https path was stripped) |
Check messages and CSV column headings are also in Japanese. Each message shows its line number and severity.
On first launch it shows a sample PAC, URL list and host table that use only example domains (the sample's comments are in Japanese).
Common questions this answers
How do I test a PAC file without deploying it?
Paste it into the tester and list the URLs you care about. You don't need a web server or a proxy.
How the URL is passed
The tester calls FindProxyForURL(url, host) for each one: host is the host name from the URL, in lower case and without the port. A line without a scheme is treated as http://.
How do I debug FindProxyForURL?
Put alert("…") calls in the script: their output appears on the result row for that URL. Script errors and timeouts also show per URL.
Why does dnsResolve or isInNet behave differently here?
A web page can't do DNS lookups, so the tester uses your host-to-IP table instead. A host that isn't in the table can't be resolved: dnsResolve returns null and isResolvable and isInNet return false.
IP addresses, localhost and IPv6
An IP address in the URL is used as is, and localhost is 127.0.0.1 unless the table says otherwise. Only IPv4 is supported, and Microsoft's IPv6 extensions (isInNetEx, dnsResolveEx and so on) raise an error.
What URL format do I use for a local .pac file?
For this tester, none: open or drop the file. A local file URL looks like file:///C:/proxy/proxy.pac on Windows (RFC 8089, E.2), but Windows' WinHTTP supports only http: and https: PAC URLs.
Why does a path rule not match https URLs?
Chrome and Edge pass only https://host/ to the PAC for https URLs, without the path or query. The tester does the same by default.
Your PAC stays on your machine and runs in a sandbox
pac-tester.html never connects to any server. The PAC runs in a Worker inside a sandboxed iframe, separate from the page.
More on safety
- Its Content-Security-Policy blocks network requests as well
- pac-tester.html includes everything it needs, including the parser library (acorn). PAC files with internal host names are safe to paste
- A PAC is a program, so it runs separately from the page. It can't touch the page, its storage, or the network
- By default your PAC isn't saved in the browser either (you can opt in)
- pac-tester.html contains no ads and no analytics (ads appear only on this page and the guide)
Guide: helper function reference, common mistakes, diff mode, FAQ
By the same author: query Active Directory without RSAT from PowerShell → ADSearch