# ctail

Tail a Static CT log, printing a one-liner per new certificate or precertificate as it arrives.

## Install

```bash
GOPRIVATE=git.ipng.ch go install git.ipng.ch/certificate-transparency/ctfetch/cmd/ctool@latest
```

## Usage

```bash
ctool tail [flags] <log-url>
```

Example:

```bash
ctool tail https://halloumi2026h2.mon.ct.ipng.ch
```

By default `ctool tail` starts at the current tree tip and prints new entries as they appear. Use `--from-leaf 0` to replay from the beginning.

## Output format

One line per entry:

```
 leaf-index  type  validity-range            issuer (up to 40 chars)          subject name
```

Example:

```
1440154358 cert  2026-03-31..2026-06-29  Let's Encrypt R13                bereavementcounselling.uk
1440154359 pre   2026-03-31..2026-06-29  ZeroSSL ECC Domain Secured Ce... alpenglowforeverfilms.com
```

- **type**: `cert` for a final certificate, `pre` for a precertificate
- **issuer**: CommonName, prefixed with the organisation name when the CN alone is terse (e.g. `R13` → `Let's Encrypt R13`)
- **subject name**: first DNS SAN, falling back to the certificate's CommonName

## Flags

| Flag | Default | Description |
|---|---|---|
| `--interval` | `15s` | How often to poll the checkpoint (minimum 1s) |
| `--from-leaf` | `-1` | Start from this leaf index; `-1` means current tree tip |
| `--rate-limit` | `2s` | Minimum time between HTTP requests (minimum 100ms) |
| `--user-agent` | `ctail/VERSION (https://git.ipng.ch/certificate-transparency/)` | User-Agent header sent with every request |

## Notes

- The interval timer starts when the checkpoint is fetched, so tile-fetch time counts against the interval and the next poll stays on schedule.
- A tile is only fetched once the checkpoint confirms it is complete (256 entries). This avoids unnecessary 404s at the tree tip.
- Status and error messages go to stderr; the entry one-liners go to stdout.