Cursor: Give the Agent Context It Cannot Guess, Then Verify
Cursor is an AI code editor whose agent works inside your repository, steered by persistent instructions: version-controlled Project Rules, global User Rules, dashboard-managed Team Rules and AGENTS.md. The engineering job is to encode what the agent cannot infer, keep it small, and back every must-hold constraint with a check that does not depend on the agent. Vibrr helps with the first two by compiling prompts and rules, and with the third by auditing the result.
Vibrr is an independent product. It is not affiliated with, endorsed by or sponsored by Cursor. Product names are trademarks of their respective owners and are used here only to describe compatibility and content.
What Cursor is and what makes its workflow different
Where a prompt-first builder generates an application from a description, Cursor assumes a codebase already exists. Its documented context system is about making that codebase legible to the agent and keeping the instructions with the repository. Vibrr summarises the workflow as: repository context, rules, agent, code changes, verification.
| Capability | What the source says | Evidence |
|---|---|---|
| Project Rules | Version-controlled rules stored in .cursor/rules as .mdc files with frontmatter metadata, scoped to the codebase. | Documented · Rules — Cursor Docs |
| User Rules and Team Rules | User Rules are global to the Cursor environment and used by Agent (Chat). Team Rules are managed from the dashboard and available on Team and Enterprise plans. | Documented · Rules — Cursor Docs |
| AGENTS.md | A plain markdown alternative to .cursor/rules, supported in the project root and in subdirectories. | Documented · Rules — Cursor Docs |
The four instruction mechanisms
| Mechanism | Where it lives | Scope |
|---|---|---|
| Project Rules | .cursor/rules as .mdc files | One codebase, version-controlled |
| User Rules | Your Cursor environment | Global to your Cursor environment; used by Agent (Chat) |
| Team Rules | Cursor dashboard | Team and Enterprise plans |
| AGENTS.md | Project root and subdirectories | Plain markdown alternative to .cursor/rules |
Project Rules can be applied in four documented modes: always, intelligently (the agent decides from the rule's description), to specific files by glob pattern, or manually by @-mention.
How Vibrr works with Cursor
- Decide what is durable. Standards that apply to every change belong in rules; a task belongs in the prompt.
- Compile the task prompt. Vibrr's compiler can turn a brief into a Cursor-shaped prompt for an existing repository, with acceptance criteria and a verification step. The app's prompt generator currently produces initial-build prompts; the existing-repository form shown on Cursor rules and prompts is compiler output that is not yet exposed there.
- Let the agent work in Cursor. Vibrr does not run inside your editor.
- Verify outside the agent. Tests, type checks and CI decide whether the change is acceptable; Vibrr's audit adds an independent read of the result.
Where rules stop applying
Two limits are stated in Cursor's own documentation, and both change how you should think about enforcement.
Documented constraints and limits for Cursor
- Documented Rules do not impact Cursor Tab or other AI features. — Rules — Cursor Docs
- Documented User Rules are not applied to Inline Edit (Cmd/Ctrl+K). — Rules — Cursor Docs
- Documented Plain .md files in .cursor/rules are ignored unless the file is named AGENTS.md. — Rules — Cursor Docs
The engineering consequence is simple: a rule is guidance the agent may follow, not a guarantee about every AI feature. Anything that must hold — no secrets in code, authorization on every route — needs a test, a linter or a CI check that fails regardless of which surface produced the change.
Architecture: what to put in rules and what to keep out
Cursor's documentation gives concrete size and content guidance, and it is worth following closely because oversized rules are a common failure.
- Keep each rule under 500 lines and split large ones into composable rules.
- Provide concrete examples or reference files rather than pasting their contents.
- Write rules like internal documentation — specific, not vague.
- Avoid copying whole style guides, documenting commands the agent already knows, or writing rules for rare edge cases.
Vibrr's addition: for each rule, ask what would change in the agent's output if the rule were deleted. If nothing, delete it.
Common mistakes
Failure modes for Cursor that a source documents or an experiment supports
Assuming rules govern every AI surface
Documented guidance — how often it happens has not been measured
- Trigger
- A must-hold constraint lives only in a rule, but the change is produced through Tab or Inline Edit.
- Symptom
- The constraint is silently absent from that output.
- Risk
- Convention or security requirements bypassed without any error.
- Prevention
- Do not rely on rules alone for must-hold constraints; back them with tests, lint and CI that run regardless of which surface wrote the code.
- Verify
- Enforce the constraint in CI and check that it fails on a deliberately violating change.
Source: Rules — Cursor Docs
Oversized or vague rules
Documented guidance — how often it happens has not been measured
- Trigger
- Copying whole style guides, documenting commands agents already know, or writing rules for rare edge cases.
- Symptom
- Rules that are long, vague and duplicate existing documentation.
- Risk
- Wasted context and weaker adherence to the rules that matter.
- Prevention
- Keep rules under 500 lines, split them into composable rules and reference files instead of copying them.
- Verify
- Review each rule: would removing it change the agent's output? If not, delete it.
Source: Rules — Cursor Docs
Production readiness and audit
Because Cursor operates on a repository you already control, production readiness is mostly the platform-independent work: authorization, secrets, states, reproducible deployment and independent review. The production checklist for AI-built apps covers it, and the security audit guide goes deeper on the riskiest part.
For a neutral look at how Cursor differs from a terminal-first agent, see Cursor compared with Claude Code.
Sources and verification
Sources reviewed for Cursor
- Rules — Cursor Docs — Cursor, read 2026-09-18. docs.cursor.com/context/rules returned a 308 permanent redirect to cursor.com/docs; the rules page at the new location was read.
Frequently asked questions
Does Vibrr replace Cursor?
No. Cursor is where the agent works; Vibrr prepares the specification and audits the result. It is an independent product, not affiliated with Cursor.
Do Cursor rules apply to Tab completions?
No. Cursor's documentation states that rules do not impact Cursor Tab or other AI features, and that User Rules are not applied to Inline Edit.
How long should a Cursor rule be?
The documentation recommends keeping rules under 500 lines and splitting large ones into composable rules.
When were these claims last checked?
On 2026-09-18, against Cursor's rules documentation. The docs.cursor.com address now redirects to cursor.com/docs.
Official and primary sources
- Rules — Cursor Docs — Cursor, read 2026-09-18. docs.cursor.com/context/rules returned a 308 permanent redirect to cursor.com/docs; the rules page at the new location was read.