Listens for Gitea webhook events and triggers code reviews on pull request comments
Streams reviews back to Gitea as PR comments
Concurrent review processing with configurable parallelism
Graceful shutdown — in-progress reviews finish before the process exits
Error tracking via Sentry
Prometheus metrics endpoint for monitoring
Tiny memory footprint (~4MB) thanks to Rust

Installation

Requirements: Rust toolchain (rustup.rs)

cargo build --release
./target/release/herald

Herald reads its configuration from environment variables (a .env file is supported):

Variable	Description
`HTTP_PORT`	Port to listen on
`BOT_NAME`	The bot's Gitea username (used to detect mentions)
`WEBHOOK_SIG_HEADER_SECRET`	Gitea webhook secret for signature verification
`OPEN_ROUTER_API_KEY`	OpenRouter API key
`OPEN_ROUTER_MODEL`	Model to use (e.g. `deepseek/deepseek-v4-flash`)
`OPEN_ROUTER_TIMEOUT`	OpenRouter request timeout in seconds
`BOT_MAX_CONCURRENT`	Maximum number of concurrent reviews
`GITEA_URL`	Base URL of your Gitea instance
`GITEA_TOKEN`	Gitea API token
`GITEA_TIMEOUT`	Gitea API request timeout in seconds
`METRICS_BIND_ADDR`	(optional) Bind address for the Prometheus metrics endpoint (e.g. `0.0.0.0:9100`). If unset, the metrics exporter is disabled.
`SENTRY_DSN`	(optional) Sentry DSN for error tracking
`RUST_LOG`	(optional) Log level, defaults to `info`

Development

The easiest way to get started is with the provided Dev Container (VS Code or Zed with the dev container extension).

Open the project and reopen it in the container — the Rust toolchain is pre-installed.

Without Dev Container, you just need a Rust toolchain:

rustup toolchain install stable
cargo run

Copy .env.example to .env and fill in your values before running.

Metrics

Herald optionally exposes a Prometheus metrics endpoint, useful for scraping with an OpenTelemetry Collector or any Prometheus-compatible scraper.

Set METRICS_BIND_ADDR (e.g. 0.0.0.0:9100) to enable it. The metrics are then available at http://<host>:9100/metrics.

Exposed metrics

Metric	Type	Description
`herald_webhooks_received_total`	counter	Total webhooks received (label: `event_type`)
`herald_webhooks_duplicate_total`	counter	Webhooks rejected as duplicates (label: `event_type`)
`herald_webhooks_channel_full_total`	counter	Webhooks dropped because the bot channel was full (label: `event_type`)
`herald_bot_tasks_active`	gauge	Bot tasks currently in progress
`herald_bot_tasks_completed_total`	counter	Bot tasks completed successfully (label: `event_type`)
`herald_bot_tasks_failed_total`	counter	Bot tasks that failed (label: `event_type`)
`herald_openrouter_cost_cents_total`	counter	Total OpenRouter cost in cents (divide by 100 for USD)

OTel collector example

receivers:
  prometheus:
    config:
      scrape_configs:
        - job_name: herald
          scrape_interval: 15s
          static_configs:
            - targets: ["herald:9100"]

service:
  pipelines:
    metrics:
      receivers: [prometheus]
      exporters: [otlp]