---
title: Functions
summary: null
url: https://www.fastly.com/documentation/reference/vcl/functions
---

Functions are predefined actions that may be invoked with arguments, and return a value. VCL offers a wide range of predefined functions, but currently does not offer the option of defining custom functions.

- [Addr](https://www.fastly.com/documentation/reference/vcl/functions/addr/)
- [Content negotiation](https://www.fastly.com/documentation/reference/vcl/functions/content-negotiation/)
- [Cryptographic](https://www.fastly.com/documentation/reference/vcl/functions/cryptographic/)
- [Date and time](https://www.fastly.com/documentation/reference/vcl/functions/date-and-time/)
- [Floating point classifications](https://www.fastly.com/documentation/reference/vcl/functions/floating-point-classifications/)
- [Headers](https://www.fastly.com/documentation/reference/vcl/functions/headers/)
- [Math logexp](https://www.fastly.com/documentation/reference/vcl/functions/math-logexp/)
- [Math rounding](https://www.fastly.com/documentation/reference/vcl/functions/math-rounding/)
- [Math trig](https://www.fastly.com/documentation/reference/vcl/functions/math-trig/)
- [Miscellaneous](https://www.fastly.com/documentation/reference/vcl/functions/miscellaneous/)
- [Query string](https://www.fastly.com/documentation/reference/vcl/functions/query-string/)
- [Randomness](https://www.fastly.com/documentation/reference/vcl/functions/randomness/)
- [Rate limiting](https://www.fastly.com/documentation/reference/vcl/functions/rate-limiting/)
- [Strings](https://www.fastly.com/documentation/reference/vcl/functions/strings/)
- [Table](https://www.fastly.com/documentation/reference/vcl/functions/table/)
- [TLS and HTTP](https://www.fastly.com/documentation/reference/vcl/functions/tls-and-http/)
- [Unicode](https://www.fastly.com/documentation/reference/vcl/functions/unicode/)
- [UUID](https://www.fastly.com/documentation/reference/vcl/functions/uuid/)