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/d-padmanabhan/agent-engineering-handbook/100-coregit clone --depth 1 https://github.com/d-padmanabhan/agent-engineering-handbookWrote 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/d-padmanabhan/agent-engineering-handbook/100-core)<a href="https://agentmods.dev/rules/d-padmanabhan/agent-engineering-handbook/100-core"><img src="https://agentmods.dev/badge/rules/d-padmanabhan/agent-engineering-handbook/100-core.svg" alt="Measured on agentmods" 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 | $0.00854 | $0.00854 |
| Opus 5 | $0.00427 | $0.00427 |
| Sonnet 5 | $0.00171 | $0.00171 |
| Haiku 4.5 | $0.00085 | $0.00085 |
Grade A, and why
100-core scanned grade A with 0 findings against 26 rules in 11 categories — prompt injection, anti-refusal, data exfiltration, privilege escalation, supply chain, agent snooping, system-prompt leakage, SSRF and excessive agency — measured 4d ago.
A static scan of the body, not an audit. Every finding is printed with the line that produced it so you can judge whether it matters here. A mod is markdown that instructs an agent; that is exactly why what it instructs is worth reading.
Nothing flagged
None of the 26 patterns this scan looks for appear in this file: no shell pipes, no recursive deletes, no credential paths, no hidden text, no instruction-override or anti-refusal phrasing, no agent-config snooping. That is not a guarantee, it is the absence of the things that are checkable.
How it starts
The opening of the file, as written. The whole thing — 60 lines — stays where its author put it; the contents beside it link to each section on GitHub.
Core Engineering Gates
This rule owns universal engineering policy only. Use the core engineering skill (${HANDBOOK_ROOT}/skills/core-engineering/SKILL.md) and the relevant domain skill for procedures, examples, and language-specific guidance.
Solve the Actual Problem
- Confirm the requested outcome and constraints from evidence before changing code.
- Make the smallest coherent change that solves the problem. Do not refactor unrelated modules, alter APIs, add dependencies, or introduce extension points without need.
- Preserve existing behavior unless the request explicitly changes it.
- State assumptions when they materially affect correctness; do not invent repository, runtime, vendor, or operational details.
Produce Complete, Maintainable Work
- Deliver complete implementations within scope. Do not leave placeholders, TODO-only stubs, omitted branches, or examples that cannot run as presented.
- Use precise domain names, cohesive units, understandable control flow, and explicit side effects, ownership, and resource lifecycles.
- Reduce meaningful duplication without creating premature abstractions or hidden coupling.
- Delete dead or misleading code when removal is in scope and behavior is preserved.
- Comments explain intent, constraints, or non-obvious decisions; they do not restate syntax.
Correctness and Failure Behavior
- Validate inputs at trust boundaries and fail with specific, safe, actionable errors.
- Handle expected failures explicitly; preserve causal context and clean up acquired resources.
- Bound network, subprocess, retry, queue, and background work with timeouts, cancellation, and lifecycle ownership.
- Protect concurrency invariants and avoid unsynchronized shared mutable state.
- Add enough structured observability to diagnose key operations and failures without logging secrets or unnecessary sensitive data.
Evidence and Current Information
- Ground claims in code, tests, diagnostics, command output, measurements, or authoritative documentation.
- For vendor, cloud, SDK, API, CLI, IaC provider, runtime, security, or authentication behavior, verify current official documentation, installed-tool help, schemas, or release notes before recommending syntax, defaults, versions, limits, or architecture.
- Label legacy guidance and explain when it still applies.
- Performance changes require a bottleneck hypothesis, expected metric impact, and a measurement plan. Do not optimize by intuition alone.
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.
- 4d ago First seen · 60 lines · 854 tokens per session scan A 4ddf793f6a4e
100-core is a cursor rule published in the GitHub repository d-padmanabhan/agent-engineering-handbook (16 stars, last pushed 4d ago), licensed MIT. It adds 854 tokens to every session, about $0.0043 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 2026-08-30.
Other cursor rules, from other repositories
angular-20
This rule provides comprehensive best practices and coding standards for Angular development, focusing on modern TypeScript, standalone components, signals, and performance optimizations.
dev-standard
Apache Superset development standards and guidelines for Cursor IDE.
cli-error-handling
CLI command error handling patterns.
prefer-direct-imports-over-module-mocks
Prefer extracting a testable core over vi.mock / vi.resetModules when unit tests need to reach production logic entangled with config, env, or singletons.
control-plane-descriptors
Control plane descriptor and instance implementation patterns.
family-instance-domain-actions
Family instance domain action implementation patterns.