> ## Documentation Index
> Fetch the complete documentation index at: https://docs.substrate.42.pe/llms.txt
> Use this file to discover all available pages before exploring further.
# substrate logs — Read Lines from the Persistent Log File
> substrate logs prints recent lines from .substrate/logs/substrate.log, written only by long-lived mcp and serve processes. Supports -n and --errors.
Run `substrate logs` to read the persistent log file written by the long-lived `substrate mcp` and `substrate serve` processes. The file is gitignored and local-only. Reading crosses a rotation boundary correctly, so `-n` is honoured even when the log just rotated.
## Usage
```shell theme={null}
substrate logs
substrate logs -n 200
substrate logs --errors
```
## Options
How many lines to print. Defaults to `50`.
Filter to errors only.
## Who Writes to the Log
Only the long-lived processes write here — `substrate mcp` and `substrate serve`. Short-lived commands do not log, so `substrate logs` after a failed one-shot command will not explain it.
An agent's handled tool errors land here, which makes `substrate logs --errors` the way an agent reviews its own error trail. Routine gate blocks and stale-version retries are excluded on purpose — they are normal operation, not faults.
## Empty States
| What you see | What it means |
| ------------------ | ------------------------------------------------------------- |
| Log file is absent | The sink never ran — no `mcp` or `serve` has logged here yet. |
| Present, no errors | It ran cleanly. |