GET /yaml

Returns YAML documents that exploit the YAML 1.1 vs 1.2 split and parser ambiguity. Default sends the Norway problem: bare `NO/YES/ON/OFF` scalars that YAML 1.1 parsers coerce to booleans while YAML 1.2 parsers leave as strings. Use ?mode= to isolate other violations: recursive anchors, duplicate keys, or tag lies.

mode norway-problem (default; bare NO/YES/ON/OFF scalars; YAML 1.1 parsers like Go yaml.v2 and older PyYAML coerce to booleans, YAML 1.2 parsers leave as strings; mixed-version pipelines disagree on the type of every value), anchor-cycle (recursive anchor reference `&a` referencing `*a`; parsers without cycle detection follow references until stack or heap is exhausted), duplicate-keys (key `host` appears twice; spec leaves behavior application-defined; parsers variously take first, take last, or error; schema validators almost always reject), tag-lie (explicit `!!int` tag applied to the string `three-point-five`; strict parsers raise a tag resolution error, loose parsers store the raw value and continue silently).

control Compare against the well-formed counterpart: not.catastrophic.io/yaml side-by-side

build a request:

violation

expect: An application/yaml response with one parser-adversity pattern. Mixed-version pipelines disagree on the type of every value; the `note` is in the X-Chaos-Yaml-Note response header.

bash

curl -si 'https://chaos.catastrophic.io/yaml?mode=norway-problem'

# pip install pyyaml ruamel.yaml
import urllib.request, yaml
resp = urllib.request.urlopen("https://chaos.catastrophic.io/yaml?mode=norway-problem")
print("Content-Type:", resp.headers.get("Content-Type"))
print("X-Chaos-Yaml-Mode:", resp.headers.get("X-Chaos-Yaml-Mode"))
print("X-Chaos-Yaml-Note:", resp.headers.get("X-Chaos-Yaml-Note"))
text = resp.read().decode()
try:
    # safe_load uses YAML 1.1 in older PyYAML; the Norway problem surfaces here.
    parsed = yaml.safe_load(text)
    print("parsed:", parsed)
except yaml.YAMLError as e:
    print("parser rejected:", e)

// npm: js-yaml (YAML 1.2)
import yaml from "js-yaml";
const res = await fetch("https://chaos.catastrophic.io/yaml?mode=norway-problem");
console.log("Content-Type:", res.headers.get("content-type"));
console.log("X-Chaos-Yaml-Mode:", res.headers.get("x-chaos-yaml-mode"));
console.log("X-Chaos-Yaml-Note:", res.headers.get("x-chaos-yaml-note"));
const text = await res.text();
try {
  console.log("parsed:", yaml.load(text));
} catch (e) {
  console.log("parser rejected:", e.message);
}

package main

// go get gopkg.in/yaml.v2  (YAML 1.1 — sees Norway problem)
// go get gopkg.in/yaml.v3  (YAML 1.2)
import (
    "fmt"
    "io"
    "net/http"

    "gopkg.in/yaml.v3"
)

func main() {
    resp, _ := http.Get("https://chaos.catastrophic.io/yaml?mode=norway-problem")
    defer resp.Body.Close()
    raw, _ := io.ReadAll(resp.Body)
    fmt.Println("Content-Type:", resp.Header.Get("Content-Type"))
    fmt.Println("X-Chaos-Yaml-Mode:", resp.Header.Get("X-Chaos-Yaml-Mode"))
    var out map[string]any
    if err := yaml.Unmarshal(raw, &out); err != nil {
        fmt.Println("unmarshal rejected:", err)
    } else {
        fmt.Println("decoded keys:", out)
    }
}

// Cargo.toml: reqwest = { version = "0.12", features = ["blocking"] }
//            serde_yaml = "0.9"  (YAML 1.2)
fn main() -> Result<(), Box> {
    let resp = reqwest::blocking::get("https://chaos.catastrophic.io/yaml?mode=norway-problem")?;
    println!("Content-Type: {:?}", resp.headers().get("content-type"));
    println!("X-Chaos-Yaml-Mode: {:?}", resp.headers().get("x-chaos-yaml-mode"));
    let text = resp.text()?;
    match serde_yaml::from_str::(&text) {
        Ok(v) => println!("parsed: {:?}", v),
        Err(e) => println!("parser rejected: {}", e),
    }
    Ok(())
}

// SnakeYAML on the classpath (YAML 1.1 by default).
import java.net.URI;
import java.net.http.*;
import org.yaml.snakeyaml.Yaml;

public class YamlChaos {
    public static void main(String[] args) throws Exception {
        var client = HttpClient.newHttpClient();
        var req = HttpRequest.newBuilder(URI.create("https://chaos.catastrophic.io/yaml?mode=norway-problem")).build();
        var resp = client.send(req, HttpResponse.BodyHandlers.ofString());
        System.out.println("Content-Type: " +
            resp.headers().firstValue("Content-Type").orElse(""));
        System.out.println("X-Chaos-Yaml-Mode: " +
            resp.headers().firstValue("X-Chaos-Yaml-Mode").orElse(""));
        try {
            Object parsed = new Yaml().load(resp.body());
            System.out.println("parsed: " + parsed);
        } catch (Exception e) {
            System.out.println("parser rejected: " + e.getMessage());
        }
    }
}

// NuGet: YamlDotNet (YAML 1.2)
using YamlDotNet.Serialization;
using var client = new HttpClient();
var resp = await client.GetAsync("https://chaos.catastrophic.io/yaml?mode=norway-problem");
Console.WriteLine($"Content-Type: {resp.Content.Headers.ContentType}");
Console.WriteLine($"X-Chaos-Yaml-Mode: " +
    $"{resp.Headers.GetValues("X-Chaos-Yaml-Mode").FirstOrDefault()}");
var text = await resp.Content.ReadAsStringAsync();
try {
    var parsed = new Deserializer().Deserialize