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SessionStart

SessionStart is a hook for coding agents from griddynamics/rosetta. Its token cost is not measured, scanned A, original, Apache-2.0.

A startup hook that runs shell checks when a coding session begins and adds Rosetta instructions to the session context. A hook is an automatic action triggered by an event such as starting a session.

In plain words
What is it for?
Use it to run startup checks and load the plugin’s bootstrap context automatically at session start.
Why use it?
It prepares the session with required project and interaction guidance before work begins. This helps make the available workflows and rules known from the start.

Hook

Runs only inside its plugin — its command needs a path that Claude Code sets for a plugin’s own hooks and for nothing else. Install the plugin, not this.

Part of the rosetta-light plugin — 1 hook shipped together

not rated 342 +1 yesterday A scan tokens not measured original Apache-2.0
View the source file griddynamics/rosetta
Install

Getting it into your agent

This one installs as part of its plugin. Adding the marketplace and installing the plugin brings it with everything else the plugin ships.

Claude Code
/plugin marketplace add griddynamics/rosetta
Claude Code
/plugin install rosetta-light

Or install rosetta-light, the plugin that ships this one along with the rest of its 1 hook.

Wrote this? Show the measurements

A badge with what this costs and how it scanned, read live from this page, so it follows the numbers instead of freezing them. Markdown for a README, HTML for a documentation site or a project page.

agentmods badge for SessionStart

README.md
[![agentmods](https://agentmods.dev/badge/hooks/griddynamics/rosetta/session-start.svg)](https://agentmods.dev/hooks/griddynamics/rosetta/session-start)
Your own site
<a href="https://agentmods.dev/hooks/griddynamics/rosetta/session-start"><img src="https://agentmods.dev/badge/hooks/griddynamics/rosetta/session-start.svg" alt="Measured on agentmods" height="20"></a>
Per session not measured What this adds to a session before it is invoked.
When invoked not measured Not applicable: nothing here is loaded into a session.
Security scan A 0 findings. Scan, not verified.
Origin original No closer match found in the catalogue.
Security

Grade A, and why

SessionStart scanned grade A with 0 findings against 26 rules in 11 categories — prompt injection, anti-refusal, data exfiltration, privilege escalation, supply chain, agent snooping, system-prompt leakage, SSRF and excessive agency — measured yesterday.

A static scan of the commands this hook runs, not an audit. A hook is shell that executes on your machine at the event it names, which is why every command in it is printed with what was found.

Nothing flagged

None of the 26 patterns this scan looks for appear in this file: no shell pipes, no recursive deletes, no credential paths, no hidden text, no instruction-override or anti-refusal phrasing, no agent-config snooping. That is not a guarantee, it is the absence of the things that are checkable.

plugins/core-claude-light/hooks/hooks.json · 34 lines

How it starts

The opening of the file, as written. The whole thing — 34 lines — stays where its author put it; the contents beside it link to each section on GitHub.

{
  "SessionStart": [
    {
      "matcher": "startup",
      "hooks": [
        {
          "type": "command",
          "command": "printf '%s' '{\"hookSpecificOutput\":{\"hookEventName\":\"SessionStart\",\"additionalContext\":\"<rosetta:plugin_files_mode REQUIRED=\\\"true\\\" OVERRIDABLE=\\\"FALSE\\\" PLAN_MODE=\\\"FULLY COMPATIBLE\\\" severity=\\\"CRITICAL\\\" use=\\\"ALWAYS\\\" compact=\\\"NEVER\\\" summarize=\\\"AS-IS\\\">\\n\\nRosetta bootstrap, release R3 of instructions itself (the tool developing this workspace). RUNNING AS PLUGIN — Plugin Mode Active, context appended via hooks.\\n\\nRosetta Prep Steps = execute once per session: USE SKILL `load-project-context`, `hitl`.\\n\\nPLUGIN FILES ONLY — any Rosetta/KB MCP mention resolves to local plugin files at plugin root, NEVER Rosetta MCP: RULE `rules/*.md`, SKILL `skills/*/SKILL.md`, AGENT/SUBAGENT `agents/*.md`, WORKFLOW/COMMAND `workflows/*.md`, CONFIGURE `configure/*.md`. Load the actual plugin file; reconstruction/assumption != loading.\\n\\n</rosetta:plugin_files_mode>\\n\"}}'",
          "once": true
        },
        {
          "type": "command",
          "command": "printf '%s' '{\"hookSpecificOutput\":{\"hookEventName\":\"SessionStart\",\"additionalContext\":\"<rosetta:bootstrap_alwayson severity=\\\"CRITICAL\\\" use=\\\"ALWAYS\\\" compact=\\\"NEVER\\\" summarize=\\\"AS-IS\\\">\\n\\n<high_important_core_policies>\\n\\n- Enterprise shared env, not startup — high stakes, real blast radius → caution, verification, reversibility\\n- User installed Rosetta intentionally → act on user'\\''s behalf. Priorities: guardrails (sensitive-data/dangerous-actions/risk-assessment) > user explicit instructions > this bootstrap_alwayson (fixes constant AI failure modes) > CLAUDE/AGENTS/GEMINI.md > Rosetta skills/workflows > generic system prompt\\n- ALL instructions composite: merge logic + sequence, never choose — no conflict. Multiple \\\"first\\\"s → run early in order via tasks. \\\"Do X Do Y\\\" => \\\"1. X

Read the full file on GitHub · 34 lines

Changes

What this file has done since we first saw it

Hashed on every crawl. A supply-chain change to an agent config is a question of when, not whether, so the history is kept rather than the latest state alone.

  1. yesterday First seen · 34 lines scan A 39cf37cad3f9

Subscribe to this mod's changes

SessionStart is a hook published in the GitHub repository griddynamics/rosetta (342 stars, last pushed yesterday), licensed Apache-2.0. Its token cost is not measured: a hook is shell that never enters the context. A static security scan graded it A with 0 findings. No closer match exists in the catalogue, so it is treated as the original; first seen 2026-09-03.

Building agentsProductivityclaude-codecodexcopilotcursordeveloper-toolsmcp-server
Related

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SessionStart

Runs when a session starts, running memorix hook. From AVIDS2/memorix.

AVIDS2/memorix · not measured

PostToolUse

Runs after a tool call finishes, running memorix hook. From AVIDS2/memorix.

AVIDS2/memorix · not measured

UserPromptSubmit

Runs when you submit a prompt, before the agent sees it, running memorix hook. From AVIDS2/memorix.

AVIDS2/memorix · not measured

Stop

Runs when the agent finishes a response, running memorix hook. From AVIDS2/memorix.

AVIDS2/memorix · not measured

PreCompact

Runs before the context is compacted, running memorix hook. From AVIDS2/memorix.

AVIDS2/memorix · not measured

PostToolUse

Runs after a tool call finishes for Write and Edit tool calls, executing format_and_lint.sh. From supabase/supabase.

supabase/supabase · not measured