Writing custom filter rules

Add your own paths, commands, hosts, and patterns to the shipping filter configs.

Each of the filter config files supports user-level overrides. The shipping defaults live in the install; your customisations live in ~/.config/grith/filters/.

This guide covers the four customisations you'll do most.

1. Add a sensitive path

Edit ~/.config/grith/filters/paths.toml:

[[deny]]
path = "${HOME}/work/customer-data/"
score = 5.0
reason = "customer data — never goes outbound"

[[deny]]
path = "internal-secrets.toml"     # any nested
score = 4.0

After saving:

grith config reload   # if daemon running

2. Add an internal egress allow

Edit ~/.config/grith/filters/egress.toml:

[[allow]]
host = "*.internal.acme.com"
score = -2.0
reason = "internal services"

[[allow]]
ip = "10.42.0.0/16"
score = -2.0
reason = "internal VPC"

3. Block a known-bad destination

# ~/.config/grith/filters/egress.toml
[[deny]]
host = "*.crypto-mining-pool.example"
score = 5.0
reason = "actually-malicious"

4. Add a team-internal secret pattern

Edit ~/.config/grith/filters/secrets.toml:

[[proxy.filters.secret_scan.custom_patterns]]
name = "acme-internal-id"
regex = "ACME-CID-[0-9]{8}"
score = 4.0
description = "internal customer ID format"

How layers work

User files are loaded on top of the shipping defaults. The rules:

Allow/deny lists — user entries are appended. Same key in both layers takes the user value.
Custom pattern arrays — user-added patterns extend the set.
Section toggles — last-write-wins.

You can't remove a shipping default — but you can override it. To effectively disable a built-in pattern, add a same-key entry with a score of 0 or with a specific allowlist annotation.

Per-team distribution

For a team setup, share these files via:

A dotfiles repo cloned to ~/.config/grith/ (manual).
A Pro centralised policy bundle (automatic, signed).

Testing your changes

grith proxy test '{"operation":"file_read","target":"/home/you/work/customer-data/foo.csv"}'

Check the filter contributions match what your new rule expects.