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.
git clone --depth 1 https://github.com/TheSethRose/DevRulesWrote 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.
[](https://agentmods.dev/rules/thesethrose/devrules/02-common-errors)<a href="https://agentmods.dev/rules/thesethrose/devrules/02-common-errors"><img src="https://agentmods.dev/badge/rules/thesethrose/devrules/02-common-errors/github.svg" alt="Measured on agentmods" height="20"></a>Or the 80×15 button, for a site that already has a row of RSS and ATOM ones. Only the verdict fits; the numbers stay here.
<a href="https://agentmods.dev/rules/thesethrose/devrules/02-common-errors"><img src="https://agentmods.dev/badge/rules/thesethrose/devrules/02-common-errors.svg" alt="Reviewed on agentmods" width="80" height="20"></a>What 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 5.1 | $0.00273 | $0.00273 |
| Opus 5.5 | $0.00109 | $0.00109 |
| Sonnet 5.5 | $0.00055 | $0.00055 |
| Haiku 4.5 | $0.00027 | $0.00027 |
Grade A, and why
02-common-errors 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 1mo ago.
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.
What it actually says
Common Mistakes & Anti-Patterns for This Project
This file lists patterns the AI should actively avoid when working on this specific codebase.
Format Guide:
Use the following structure for each entry:
### MISTAKE: [Short Description of the Mistake]
- [PATTERN]: Describe when or how the mistake typically occurs.
- [BAD_EXAMPLE]: (Optional) Show a concise code snippet of the incorrect way.
- [GOOD_EXAMPLE]: Show a concise code snippet of the correct way.
- [SOLUTION/RULE]: Clearly state the rule or the correct approach to follow.
- [CONTEXT/REASON]: (Optional) Explain why the correct way is preferred (e.g., performance, maintainability, project standard).
- [REFERENCE]: (Optional) Link to relevant documentation, style guide section, or issue tracker.
Project-Specific Mistakes (User: Add your entries below)
MISTAKE:
- [PATTERN]:
- [BAD_EXAMPLE]:
- [GOOD_EXAMPLE]:
- [SOLUTION/RULE]:
- [CONTEXT/REASON]:
- [REFERENCE]:
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.
- 1mo ago First seen · 32 lines · 273 tokens per session scan A 01c960134a95
02-common-errors is a cursor rule published in the GitHub repository TheSethRose/DevRules (26 stars, last pushed 1y ago), licensed MIT. It adds 273 tokens to every session, about $0.0011 per session on Opus 5.5. 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 2026-08-30.
Other cursor rules, from other repositories
pyspark-etl-best-practices-cursorrules-prompt-file
Cursor rules for PySpark ETL development with code style, joins, window functions, map operations, and Iceberg patterns.
project-epic-template-cursorrules-prompt-file
Cursor rules for project development with epic template integration.
react-tanstack-router-query-cursorrules-prompt-file
Cursor rules for React SPAs combining TanStack Router v1 and TanStack Query v5 for zero-loading-spinner routing and type-safe server state.
ankra-cli
Ankra CLI rules and best practices for managing Kubernetes clusters via the Ankra platform.
playwright-integration-testing-cursorrules-prompt-file
Cursor rules for Playwright development with integration testing.
go-backend-scalability-cursorrules-prompt-file
Cursor rules for Go development with backend scalability.