Make your first request

In this quickstart, you start a local mock of the KRKplaysTennis API, list players, and read one player’s rating. It takes less than 5 minutes.

KRKplaysTennis is fictional, so there’s no live server. The mock is Prism: it reads the OpenAPI spec of the API and answers each request with the examples in it.

Before you begin

• Node.js 22 or later. You need it to run the mock, and for the JavaScript examples.
• A macOS or Linux terminal. On Windows, use WSL.
• For the Python examples, Python 3.10 or later with the requests package (pip install requests).

Steps

1. Start the mock:

   npx @stoplight/prism-cli@5 mock https://saverio-cirillo.com/krk-plays-tennis-api/openapi.yaml

   The first run downloads Prism, which takes a few seconds. When the mock is ready, the last line of the output is:

   Prism is listening on http://127.0.0.1:4010

   Keep this terminal open.

2. In a new terminal, set the base URL and an API key:

   export KRK_API_URL=http://127.0.0.1:4010
   export KRK_API_KEY=quickstart-key

   The mock accepts any API key, as long as you send one. Every example in these docs reads these two variables, so the same code works with the mock and with a real key.

   To check the variables, run echo $KRK_API_URL. The output is http://127.0.0.1:4010.

3. List the players:

   curl

   curl --silent "$KRK_API_URL/players" \
     --header "X-API-Key: $KRK_API_KEY"

   JavaScript

   Save this code as list-players.mjs, then run node list-players.mjs:

   const response = await fetch(`${process.env.KRK_API_URL}/players`, {
     headers: { 'X-API-Key': process.env.KRK_API_KEY },
   });
   if (!response.ok) throw new Error(`Request failed: ${response.status}`);
   
   console.log(JSON.stringify(await response.json(), null, 2));

   Python

   Save this code as list_players.py, then run python3 list_players.py:

   import json
   import os
   
   import requests
   
   response = requests.get(
       f"{os.environ['KRK_API_URL']}/players",
       headers={"X-API-Key": os.environ["KRK_API_KEY"]},
   )
   response.raise_for_status()
   
   print(json.dumps(response.json(), indent=2))

   The response lists three players: Kasia W., Marta Z., and Ola K. Each player has a rating with a value and a confidence. next_cursor is null, because there are no more pages. The start of the response looks like this:

   {
     "data": [
       {
         "id": "plr_9fz3tr6wn1",
         "display_name": "Kasia W.",
         "self_assessed_ntrp": 4,
         "rating": { "value": 1499, "confidence": 70 },

4. Get the rating of Ola K., whose player ID is plr_2b7xq9mhk4:

   curl

   curl --silent "$KRK_API_URL/players/plr_2b7xq9mhk4/rating" \
     --header "X-API-Key: $KRK_API_KEY"

   JavaScript

   Save this code as get-rating.mjs, then run node get-rating.mjs:

   const playerId = 'plr_2b7xq9mhk4';
   
   const response = await fetch(`${process.env.KRK_API_URL}/players/${playerId}/rating`, {
     headers: { 'X-API-Key': process.env.KRK_API_KEY },
   });
   if (!response.ok) throw new Error(`Request failed: ${response.status}`);
   
   console.log(JSON.stringify(await response.json(), null, 2));

   Python

   Save this code as get_rating.py, then run python3 get_rating.py:

   import json
   import os
   
   import requests
   
   player_id = "plr_2b7xq9mhk4"
   
   response = requests.get(
       f"{os.environ['KRK_API_URL']}/players/{player_id}/rating",
       headers={"X-API-Key": os.environ["KRK_API_KEY"]},
   )
   response.raise_for_status()
   
   print(json.dumps(response.json(), indent=2))

   The response shows Ola’s rating after one rated match:

   {
     "player_id": "plr_2b7xq9mhk4",
     "value": 1432,
     "confidence": 30,
     "k_factor": 48,
     "rated_matches": 1,
     "last_rated_match_at": "2026-10-10T18:00:00+02:00",
     "updated_at": "2026-10-10T20:43:12Z"
   }

   Ola started at 1400, from a self-assessed NTRP level of 3.5. Winning that first match raised the rating by 32 and the confidence from 20 to 30.

You’ve made your first two requests to the KRKplaysTennis API.

Next steps

• How ratings work: why Ola’s rating went from 1400 to 1432.
• Explain a rating change: reproduce that change from the API data.
• Find opponents for a player: suggest fair matches.
• Authenticate with an API key: how API keys work, and how to keep yours out of your code.
• API reference: the parameters and responses of every operation.