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wtf is c-ares?

petere/c-ares — explained in plain English

Analysis updated 2026-07-18 · repo last pushed 2019-09-20

Audience · developerComplexity · 4/5DormantLicenseSetup · hard

TL;DR

c-ares is a C library for asynchronous DNS lookups, letting programs resolve many domain names at once without blocking or freezing.

Mindmap

mindmap
  root((repo))
    What it does
      Async DNS lookups
      Non-blocking queries
      Handles many requests at once
    Tech stack
      C
    Use cases
      High concurrency servers
      Responsive desktop apps
      Systems software
    Audience
      Systems developers
      Backend engineers
    Setup
      Build from source
      Follows strict C standards

Code map

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Why would anyone build with this?

REASON 1

Resolve DNS lookups for thousands of clients on a server without blocking on each request.

REASON 2

Keep a desktop app's UI responsive while it looks up addresses in the background.

REASON 3

Add asynchronous DNS resolution to system-level C software that handles many concurrent connections.

REASON 4

Build embedded or cross-platform software that needs DNS lookups with minimal dependencies.

What's in the stack?

C

How it stacks up

petere/c-ares0verflowme/alarm-clock0verflowme/seclists
LanguageCSS
Last pushed2019-09-202022-10-032020-05-03
MaintenanceDormantDormantDormant
Setup difficultyhardeasyeasy
Complexity4/52/51/5
Audiencedevelopervibe coderops devops

Figures from each repo's GitHub metadata at analysis time.

How do you spin it up?

Difficulty · hard Time to first run · 1h+

Requires building from source, targets low-level systems work across many platforms.

Use freely for any purpose, including commercial use, under a permissive MIT-style license.

Wtf does this do

c-ares is a C library that lets programs look up web addresses (DNS queries) without freezing. Normally, when an application asks "what's the IP address for google.com?", the program has to wait for an answer before doing anything else. c-ares flips this around, it lets you ask the question and then immediately move on to other work while the answer comes back in the background. This is especially useful for servers handling many clients at once, or for apps with a user interface where freezing would feel sluggish. The library works by handling DNS lookups asynchronously, meaning you can send multiple address-lookup requests at the same time and process their results whenever they arrive. You don't have to sit around waiting for each one to finish before starting the next. This matters a lot in real-world software: a web server talking to thousands of clients, or a desktop app responding to user clicks, can't afford to block and wait for network answers. The project is a maintained, well-established C library, it's mature enough to be included in major open-source projects and follows security best practices. If you're building system-level software in C that needs to talk to multiple services or handle many concurrent connections, this library solves the "don't block on DNS" problem for you. It's distributed under a permissive MIT-style license, so it's free to use and modify. The README notes that this is a fairly low-level, systems-oriented project. It requires building from source on your platform, and the maintainers keep strict standards around code style and compiler compatibility, they assume only basic C features so the library works everywhere from old embedded systems to modern servers.

Yoink these prompts

Prompt 1
Show me how to use c-ares to look up multiple domain names asynchronously in a C program.
Prompt 2
Help me integrate c-ares into a server so DNS lookups don't block client connections.
Prompt 3
Explain how c-ares handles concurrent DNS requests without waiting for each one to finish.
Prompt 4
Walk me through building c-ares from source on my platform following this repo's conventions.

Frequently asked questions

wtf is c-ares?

c-ares is a C library for asynchronous DNS lookups, letting programs resolve many domain names at once without blocking or freezing.

Is c-ares actively maintained?

Dormant — no commits in 2+ years (last push 2019-09-20).

What license does c-ares use?

Use freely for any purpose, including commercial use, under a permissive MIT-style license.

How hard is c-ares to set up?

Setup difficulty is rated hard, with roughly 1h+ to a first successful run.

Who is c-ares for?

Mainly developer.

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