URL Encoding Explained Why Your Spaces Turn Into %20 (And How to Fix It)

更新日 2月 6, 2026

URLには特殊文字は使用できません。URLエンコーディングとは何か、いつ使用するか、そして無料ツールでURLを即座にエンコードまたはデコードする方法を学びましょう。

URL Encoding Explained: Why Your Spaces Turn Into %20 (And How to Fix It)

Ever copy a URL with spaces and watch it magically transform into a mess of percent signs and numbers? That”s URL encoding in action — the unsung hero keeping the internet from completely falling apart. 🔗

If you”ve ever pasted a link into an email only to have it break, or wondered why your API request is returning garbage, URL encoding (or the lack thereof) is probably the culprit. Let”s demystify this stuff and show you how to encode and decode URLs instantly.

What Is URL Encoding, Anyway?

URLs can only contain a limited set of characters. Letters, numbers, and a handful of symbols make the cut. Everything else — spaces, ampersands, question marks, emojis, non-ASCII characters — needs to be converted into a format URLs can handle.

That format is percent-encoding. Each unsafe character gets replaced with a percent sign followed by its hexadecimal value. So:

space → %20
& → %26
= → %3D
? → %3F
@ → %40

Without this encoding, browsers and servers would have no idea where a URL parameter ends and another begins. Chaos would ensue. Cats and dogs living together. Mass hysteria.

When You Actually Need URL Encoding

You”ll want to encode URLs whenever you”re:

Building API requests — Query parameters with user input need encoding, or your requests will break spectacularly
Passing data in URLs — Sharing links with special characters? Encode them first
Handling form data — Form submissions use URL encoding by default
Working with non-ASCII text — Japanese, Arabic, emoji? All need encoding

Basically, if you”re putting anything user-generated into a URL, encode it. Your future self debugging mysterious 400 errors will thank you.

URL Encoding vs Base64: Not the Same Thing

Quick clarification because this trips people up: URL encoding and Base64 encoding are completely different animals.

URL encoding only escapes “unsafe” characters and keeps everything else readable. Hello World becomes Hello%20World — still pretty recognizable.

ベース64 converts all data into a different alphabet entirely. Hello World becomes SGVsbG8gV29ybGQ= — completely unreadable gibberish (to humans, anyway).

Use URL encoding for URLs. Use Base64 when you need to embed binary data in text. Simple. 💡

The Easy Way: IO Tools URL Encoder/Decoder

Sure, you could write JavaScript to handle this (encodeURIComponent() is your friend), but why bother when you can just paste text and get instant results?

私たちの URLエンコーダー/デコーダー does exactly what it says on the tin:

Paste your text, select “Encode,” get URL-safe output
Paste an encoded URL, select “Decode,” see the original text
Real-time processing — no waiting, no page reloads
Uses standard JavaScript methods under the hood, so results are reliable

No sign-up required. No ads in your face. Just a tool that does one thing well.

Common URL Encoding Gotchas

A few things to watch out for:

Double encoding — If something”s already encoded, encoding it again turns %20 の中へ %2520. Always decode first if you”re unsure.
Plus signs — In query strings, + sometimes represents a space. This is a legacy thing from form submissions. Our tool handles this correctly.
Path vs query encoding — Slightly different rules apply to the URL path versus query parameters. Our tool uses encodeURIComponent, which is the safest choice for most cases.