Gampangin
Menu
Enter
Client-side

Reference

URI Reserved and Unreserved Characters

The RFC 3986 character classes and the hexadecimal escapes that keep a URI unambiguous.

By Gampangin· Published · Updated · Reviewed by Gampangin· 1 min read· URL Encoding

AI-assisted draft. Editorial responsibility: Gampangin.

RFC 3986 divides URI characters into reserved and unreserved. Reserved characters delimit structure; unreserved characters are safe as data. A character outside both sets, and any reserved character used as data, is percent-encoded.

Character roles in RFC 3986
ClassCharactersUse
UnreservedA–Z a–z 0–9 - . _ ~safe as data
Gen-delims: / ? # [ ] @structure delimiters
Sub-delims! $ & ' ( ) * + , ; =component delimiters

01Limitations

RFC 3986 defines the generic syntax. Application profiles such as HTTP add rules for specific components and query formats.

Sources

  1. RFC 3986: Uniform Resource Identifier (URI): Generic Syntax — IETF (accessed 2026-09-27)
  • ReferenceCSV Format Reference

    A concise reference for RFC 4180 CSV: delimiters, quoting, escaping, line endings and encodings.

  • ReferencePercentage Points vs Percent

    The difference between a change in percentage points and a percent change, with concrete examples.

  • ReferenceUUID Format, Versions, and Variants

    The 8-4-4-4-12 textual layout, the version and variant fields, and the RFC that defines them.

  • ReferenceWhat is Base64?

    A reference for Base64 encoding: what it is, its alphabet, and its size overhead.

  • CategoryURL Encoding

    Percent-encode URLs and understand the reserved characters that carry structure.