error-messages

A set of rules for writing error messages that include useful context and possible fixes.

In plain words
What is it for?
Use it when adding or reviewing validation errors, runtime errors, and other messages shown during failures.
Why use it?
It helps developers understand what went wrong and what they can try next instead of receiving vague failures.

Cursor rule for Cursor

Install

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.

agentmods
npx agentmods add rules/jesseoue/cursor-rules/error-messages
Clone the repo
git clone --depth 1 https://github.com/jesseoue/cursor-rules

Made for: Cursor.

Per session 9 Only the description is in the session, so the agent can decide to use it. The body loads when it is invoked.
When invoked 324 The whole file, excluding the scripts and references it only reads on demand.
Security scan B 1 finding. Scan, not verified.
Origin unknown No closer match found in the catalogue.
Token cost

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.

ModelPer sessionOnce invoked
Fable 5 $0.00009 $0.00324
Opus 5 $0.00005 $0.00162
Sonnet 5 $0.00002 $0.00065
Haiku 4.5 $0.00001 $0.00032

Measured yesterday against content hash 9e39b058aef1, method: parsed. Prices are Anthropic first-party input rates as of 2026-08-30, from the pricing page.

Security

Grade B, and why

error-messages scanned grade B with 1 finding 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.

Asks for rootmediumPrivilege escalation

A mod that escalates privileges can change anything on the machine, not only the project.

1. Check if PostgreSQL is running: `sudo systemctl status postgresql`
.cursor/rules/error-messages.mdc · 42 lines

The source is not reproduced here

No licence file

A repository with no LICENSE is all rights reserved by default, so the body is not copied here. The metadata, the measurements and the link are.

Read it on GitHub

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 · 42 lines · 9 tokens per session scan B 9e39b058aef1

Subscribe to this mod's changes

error-messages is a cursor rule published in the GitHub repository jesseoue/cursor-rules (6 stars, last pushed 10mo ago), with no licence file. It adds 9 tokens to every session and 324 once invoked, about $0.0000 per session on Opus 5. A static security scan graded it B with 1 finding (asks for root). No closer match exists in the catalogue, so it is treated as the original; first seen 2026-08-31.