aws-lambda

A set of coding rules for AWS Lambda, Amazon’s service for running code in response to events without managing servers. It covers function structure, input validation, errors, retries, state, and performance.

In plain words
What is it for?
Use it when creating or reviewing Lambda handlers, business logic, data-access code, external-service integrations, and TypeScript or Python functions.
Why use it?
It helps keep event-driven functions small, testable, safe to retry, and separated from infrastructure details.

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/jimmypocock/cursor-rules/aws-lambda
Clone the repo
git clone --depth 1 https://github.com/jimmypocock/cursor-rules

Made for: Cursor.

Per session 5 Only the description is in the session, so the agent can decide to use it. The body loads when it is invoked.
When invoked 892 The whole file, excluding the scripts and references it only reads on demand.
Security scan A 0 findings. Scan, not verified.
Origin original 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 $0.00005 $0.00892
Opus 5 $0.00003 $0.00446
Sonnet 5 $0.00001 $0.00178
Haiku 4.5 $0.00001 $0.00089

Measured yesterday against content hash 93ce70ed7edd, method: parsed. Prices are Anthropic first-party input rates as of 2026-08-30, from the pricing page.

Security

Grade A, and why

aws-lambda 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.

.cursor/rules/aws-lambda.mdc · 114 lines

How it starts

The opening of the file, as written. The whole thing — 114 lines — stays where its author put it; the contents beside it link to each section on GitHub.


Description: AWS Lambda Function Best Practices Globs: /lambda//.ts, /functions//.ts, /src//.ts, /lambda//.py, /functions//.py, /src//.py

AWS Lambda Development Standards

@base.mdc @typescript.mdc

Lambda Function Design

  • Follow single responsibility principle for each Lambda function
  • Keep functions focused on one specific task or domain operation
  • Separate business logic from infrastructure concerns
  • Create pure functions where possible for easier testing
  • Implement idempotent functions to handle retries safely
  • Design functions to be stateless
  • Avoid long-running processes; break them into smaller steps

Handler Structure

  • Keep handlers thin, delegating to service or business logic layers
  • Validate input parameters early in the function
  • Return properly structured responses
  • Add custom context to errors for better debugging
  • Follow these layers in Lambda implementation:
    1. Handler layer (entry point)
    2. Service layer (business logic)
    3. Data access layer (repository pattern)
    4. External service integrations

Performance Optimization

  • Initialize SDK clients and database connections outside the handler
  • Cache static assets and reference data between invocations
  • Implement connection pooling for database access
  • Utilize provisioned concurrency for latency-sensitive functions
  • Set appropriate memory allocation based on function needs
  • Use environment variables for configuration
  • Implement backoff strategies for external service calls
  • Leverage AWS SDK client reuse whenever possible

Cold Start Mitigation

  • Keep function code and dependencies lightweight
  • Use AWS Lambda Layers for large dependencies
  • Use provisioned concurrency for critical paths
  • Implement warmup mechanisms for important functions
  • Consider using NodeJS or native runtime for faster cold starts
  • Choose appropriate memory settings to balance CPU/memory needs
  • Set reasonable function timeouts

Error Handling

  • Implement comprehensive error handling and logging
  • Add context information to errors
  • Use structured logging with correlation IDs
  • Distinguish between client errors (4xx) and server errors (5xx)
  • Use try/catch blocks with specific error types
  • Handle retries with exponential backoff
  • Consider implementing circuit breakers for external services

Read the full file on GitHub · 114 lines

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 · 114 lines · 5 tokens per session scan A 93ce70ed7edd

Subscribe to this mod's changes

aws-lambda is a cursor rule published in the GitHub repository jimmypocock/cursor-rules (8 stars, last pushed 1y ago), licensed MIT. It adds 5 tokens to every session and 892 once invoked, about $0.0000 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.