Shim CLI · Open source

The privacy and control layer for coding agents

Shim CLI runs on your machine next to Claude Code, Codex and Copilot. It finds secrets and personal data in what your agent sends, masks what it can before the model reads it, and shows what each session cost.

Install in a minuteView on GitHub(opens in a new tab)
  • Apache-2.0
  • v1.0.0
  • macOS and Linux
  • Python 3.10 to 3.13

Install

uv · in your terminal, adds shim to ~/.local/bin

uv tool install --python 3.12 --compile-bytecode shim
Other install options

Try this prompt

in Copilot CLI, or Claude Code and Codex with enforce mode on

Hello, my email is "alice@example.com" and my IBAN is "TR33 0006 1005 1978 6457 8413 26". What is my email domain and the last 4 digits of my IBAN?

What it does

Two commands, two questions

Protect every session automatically, or measure one session to see where your tokens and data actually went.

shim install claude

Mask sensitive data, every session

Installs a native hook in your agent. When the agent reads a file or a tool result holding a key, an IBAN or an email, the model gets a placeholder like <SECRET_1> instead of the value.

shim watch -- claude

See what a session sent and cost

Runs a local proxy for one command and reports tokens, spend and every secret or personal value that went past. It changes nothing, writes no request to disk and leaves nothing behind.

Quickstart

Start with three commands

Pick your coding agent. Nothing here needs an account, an API key or a network call to shim.

  1. Install the CLI

    uv tool install --python 3.12 --compile-bytecode shim
    Use pipx instead
    pipx install --python python3.12 shim

  2. Connect it to Claude Code

    Preview the change first, then install the hook.

    shim install claude --dry-runshim install claude

  3. Check that it works

    shim doctor claude

    Then use Claude Code as you normally do. Masks secrets and personal data in the files and tool results your agent reads, before the model sees them.

Prefer a plugin?

Install from the Claude Code marketplace instead of running shim install. Use one method, not both.

/plugin marketplace add GetSHIM/shim-cli/plugin install shim-cli@shim-cli

What it detects

Found locally, checked where it can be

IBANs and Turkish IDs are verified by checksum, so a mistyped number is not reported. Add your own project names or host formats as patterns.

  • Email addresses
  • Phone numbers
  • Credit cards
  • IBANs
  • Turkish national IDs
  • Turkish tax IDs
  • API keys and secrets
  • Database URIs
  • IP addresses
  • MAC addresses
  • US SSNs
  • Your own patterns

What you see

A summary at the end of the turn

A real Claude Code session on a customer file. Every value was replaced before the model saw it, and a document trying to give the agent orders was flagged.

masked    60 EMAIL  (Read customers.csv)
          60 IBAN  (Read customers.csv)
          60 PHONE  (Read customers.csv)
          60 TR_NATIONAL_ID  (Read customers.csv)
flagged   1 INSTRUCTION_OVERRIDE  (Read runbook.md)
          1 HIDDEN_TEXT  (Read runbook.md)
overhead  62 ms median, 119 ms p95

How it is verified

Measured on the released build

tests run on every release
1,900+tests run on every release
median hook cost, interpreter start included
70 msmedian hook cost, interpreter start included
detector cases, graded on exact output
589detector cases, graded on exact output
accounts, API keys or telemetry added by shim
0accounts, API keys or telemetry added by shim

Before you rely on it

What Shim CLI does not do

  • By default a secret you type into a Claude Code or Codex prompt is reported, not stopped. Turn on enforce mode to block the prompt instead.
  • The output of a failed tool call is not masked. Claude Code sends it to a hook event shim does not install.
  • Detection is best-effort and can miss a value. It narrows exposure, it is not a data-loss prevention boundary.
  • shim watch supports Claude Code only for now.
Read the full privacy boundary(opens in a new tab)

Free, open source, yours to read

The whole CLI is on GitHub under Apache-2.0. Read the detector, run the tests, open an issue or send a pull request.

Install Shim CLIStar on GitHub(opens in a new tab)

For your whole team

Protect your applications too

Shim Enterprise puts the same protection in front of the AI traffic your products send, with audit, budgets and roles.

Explore Shim Enterprise