Getting it into your agent
One page per mod, every tool's command on it. A separate URL per tool would split the same page into five that compete with each other.
npx agentmods add rules/markmhendrickson/foundation/environment_variables_env_filegit clone --depth 1 https://github.com/markmhendrickson/foundationWhat it costs to keep this loaded
Counted locally with the o200k_base tokenizer, which is exact for GPT models; Claude uses its own tokenizer and its counts differ. Treat this as one consistent yardstick across the catalogue rather than a bill. Prices are per million input tokens.
| Model | Per session | Once invoked |
|---|---|---|
| Fable 5 | $0.00027 | $0.01010 |
| Opus 5 | $0.00014 | $0.00505 |
| Sonnet 5 | $0.00005 | $0.00202 |
| Haiku 4.5 | $0.00003 | $0.00101 |
Grade A, and why
environment_variables_env_file scanned grade A with 0 findings against 26 rules in 11 categories — prompt injection, anti-refusal, data exfiltration, privilege escalation, supply chain, agent snooping, system-prompt leakage, SSRF and excessive agency — measured yesterday.
A static scan of the body, not an audit. Every finding is printed with the line that produced it so you can judge whether it matters here. A mod is markdown that instructs an agent; that is exactly why what it instructs is worth reading.
Nothing flagged
None of the 26 patterns this scan looks for appear in this file: no shell pipes, no recursive deletes, no credential paths, no hidden text, no instruction-override or anti-refusal phrasing, no agent-config snooping. That is not a guarantee, it is the absence of the things that are checkable.
How it starts
The opening of the file, as written. The whole thing — 121 lines — stays where its author put it; the contents beside it link to each section on GitHub.
Environment Variables from .env File Rule
Reference: foundation/agent_instructions/cursor_rules/configuration_management.mdc - Configuration management
Purpose
Ensures agents always check the .env file for environment variables before assuming they are unset or asking users for values. The .env file is the primary source of environment variable configuration in repositories.
Trigger Patterns
When any of the following occur, agents MUST check the .env file first:
- Environment variable is referenced in code, scripts, or configuration
- Environment variable appears to be unset (empty value from
process.envor$VAR) - User mentions an environment variable that needs to be used
- Scripts require environment variables for execution
- Configuration depends on environment variables
Agent Actions
Step 1: Check .env File First
When an environment variable is needed:
-
Check if
.envfile exists:test -f .env && echo ".env exists" || echo ".env not found" -
Read the variable from
.env:grep "^VARIABLE_NAME=" .env # Or with value extraction: grep "^VARIABLE_NAME=" .env | cut -d'=' -f2 | tr -d '"' -
For multiple variables or complex parsing:
# Use grep with pattern matching for multiple variable names grep -E "^DATA_DIR=|^ALTERNATE_DATA_DIR=" .env
Step 2: Use the Value from .env
- Extract the value from
.envfile - Use the value directly in commands or scripts
- Do NOT assume the variable is unset just because it's not in the current shell environment
Step 3: Handle Missing Variables
If the variable is not in .env:
- Check
env.examplefor expected variables - Check repository documentation for setup instructions
- Check if the variable is managed in the secrets snapshot (SOPS+age; materialize offline rather than reading 1Password directly)
- Only then ask the user if the variable is truly missing
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.
- yesterday First seen · 121 lines · 27 tokens per session scan A 4e8df47f4876
environment_variables_env_file is a cursor rule published in the GitHub repository markmhendrickson/foundation (2 stars, last pushed 1mo ago), licensed MIT. It adds 27 tokens to every session and 1,010 once invoked, about $0.0001 per session on Opus 5. 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 2026-08-31.
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