Local development

Discord only talks to a public HTTPS URL. To develop a bot, run it on your machine, give it a public URL with a tunnel, point a development application at that URL, and register the Commands in a test server, where changes show up at once.

Start from a template

cargo-generate creates a bot with a /hello Command, a Sync binary, a test and the platform’s configuration:

cargo install cargo-generate
cargo generate --git https://github.com/BlueFrog130/composure-rs templates/cloudflare --name my-bot
cargo generate --git https://github.com/BlueFrog130/composure-rs templates/tokio --name my-bot

A development application

Create a second application in the Developer Portal for development, so pointing it at your machine never touches the bot people use. Note its public key (General Information), its application id, and its bot token (Bot), then add it to a test server through Installation.

Running the bot

On Workers, wrangler dev serves the Worker locally and reads its secrets from .dev.vars:

cp .dev.vars.example .dev.vars   # DISCORD_PUBLIC_KEY, DISCORD_TOKEN
npx wrangler dev                 # http://localhost:8787

On a server, run it as is; the template reads .env:

cp .env.example .env             # DISCORD_PUBLIC_KEY, DISCORD_TOKEN, DISCORD_APPLICATION_ID
cargo run                        # http://localhost:8080

A tunnel

A tunnel gives the local port a public HTTPS URL:

cloudflared tunnel --url http://localhost:8787   # prints https://<random>.trycloudflare.com
ngrok http 8787                                  # or ngrok

Use port 8080 for the tokio bot. Quick tunnels get a new URL each time they start; a named tunnel (or a reserved ngrok domain) keeps one.

The Interactions Endpoint URL

Paste the tunnel’s URL into the development application’s Interactions Endpoint URL (General Information) and save. Discord checks it before accepting: it sends a signed Ping, which must be answered with a Pong, and requests with invalid signatures, which must be refused with 401. The Adapters do both, so a save that fails means the bot isn’t reachable at that URL, or its DISCORD_PUBLIC_KEY belongs to another application.

For Webhook Events, set the Webhook Events URL to the same URL plus /events and enable the events you handle.

Commands in a test server

Global Commands are shared by every server; while developing, send them all to your test server instead, where Discord shows changes immediately:

cp .env.example .env             # DISCORD_TOKEN, DISCORD_APPLICATION_ID (Workers template)
cargo run --bin sync -- --guild <test server id>

--guild ignores Scopes and leaves global Commands alone. Copy a server’s id with Developer Mode on (User Settings › Advanced), from the server’s context menu. Run it again whenever a Command’s name, Options or description change; handler code changes only need the bot restarted.

Logs and tests

wrangler dev prints what the Worker logs; the tokio template logs to stderr, filtered by RUST_LOG (RUST_LOG=info,composure=debug shows every Interaction). Handler errors are logged with their causes, and the user gets an ephemeral message instead of Discord’s failure (Troubleshooting).

Most changes don’t need Discord at all: cargo test runs the Commands against stand-ins (Testing).