When should I use encodeURIComponent?

For any value you're inserting into a query param, path segment, or fragment — anything that shouldn't preserve URL syntax like & or =.

Why did decoding throw an error?

Malformed percent-escapes (e.g. a lone %) are rejected by the spec. Fix the input or fall back to a lenient decoder.

URL Encoder / Decoder

Encode and decode URLs with encodeURI vs encodeURIComponent options.

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Use encodeURIComponent (recommended for query params)

Input

Encoded

https%3A%2F%2Fpromptfoo.tech%2Fsearch%3Fq%3Dmcp%20servers%20%26%20agents

Decoded

https://promptfoo.tech/search?q=mcp servers & agents

Runs entirely in your browser — nothing you paste is sent to a server.

About this tool

Encode or decode URLs and query strings with the right helper — encodeURI for whole URLs, encodeURIComponent for individual params. Both sides update live.

How it works

Paste a URL or query fragment.
Toggle between encodeURI and encodeURIComponent.
See encoded and decoded output side by side.

When to use it

Debugging why a URL parameter reaches the server malformed.
Building tracking links safely.
Round-tripping JWTs or Base64 values embedded in query strings.

FAQs

Related resources

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