Lambda Logs Viewer

A fast, local web UI to browse AWS Lambda invocations and their CloudWatch logs. Point it at an AWS account, pick a function, and drill into recent invocations and logs - with search, level filters, per-invocation metrics (duration, memory, cold start) and reconstructed success/error status.

It runs entirely on your machine. Route loaders run on a local server and call AWS directly, so credentials never reach the browser and nothing is sent to any third party.

Browser (React UI)  ──►  local server (loaders)  ──►  AWS Lambda + CloudWatch + STS

Status: this tool talks to your real AWS account in read-only fashion. It only ever reads (list functions, read logs, get caller identity) - see IAM permissions.

Quick start

You need Node.js 20+ and AWS credentials available in your shell (see AWS credentials).

Run it without installing anything:

# with an already-logged-in shell (env vars / SSO)
npx lambda-logs-viewer

# or pin a named profile from ~/.aws/config
AWS_PROFILE=my-profile npx lambda-logs-viewer

# or, if you use aws-vault
aws-vault exec my-profile -- npx lambda-logs-viewer

Then open the URL it prints (default http://localhost:3000).

Install it globally if you prefer:

npm install -g lambda-logs-viewer
lambda-logs-viewer

Features

• Function rail - searchable, always-visible list of the account's Lambdas; resize it and your width preference is remembered.
• Invocations - recent invocations reconstructed from CloudWatch START/END/REPORT markers, with real status detection (success / error / unknown), status filter, time-range selector and opt-in auto-refresh.
• Per-invocation logs - the REPORT line is rendered as a card: duration, billed duration, memory usage bar, and a highlighted cold start when an init duration is present.
• Inline JSON - log lines containing JSON get a collapsible viewer.

AWS credentials

The tool is scoped to a single AWS account/region, resolved once at startup. There is no in-app account switching. Resolution order:

1. Static credentials already in the environment (AWS_ACCESS_KEY_ID / AWS_SECRET_ACCESS_KEY / AWS_SESSION_TOKEN) - e.g. injected by aws-vault or CI. These take precedence.
2. Otherwise, AWS_PROFILE selects a named profile from ~/.aws/config.
3. Otherwise, the standard AWS provider chain (shared-config default, SSO, …).

Configuration

All environment variables are optional:

| Variable | Role | Default | | ------------- | ---------------------------------------------------------- | ----------------------------------- | | AWS_PROFILE | Named profile - source of credentials, account and region | ambient shell credentials | | AWS_REGION | Region override | profile / env region, else built-in | | PORT | Local server port | 3000 |

You can override each variable:

PORT=4546 npx lambda-logs-viewer

IAM permissions

Read-only. The identity you run as needs:

• lambda:ListFunctions
• logs:FilterLogEvents, logs:GetLogEvents, logs:DescribeLogStreams
• sts:GetCallerIdentity

How it works

Invocations are inferred from CloudWatch logs, not from a metrics API: the tool reads a function's log group over the selected time range and reconstructs invocations by grouping the runtime's START / END / REPORT markers by Request ID. A consequence: a Lambda that was never invoked (or whose logs have expired) shows no invocations.

Contributing

Contributions are welcome. The project is a single React Router v7 app (framework mode) with a clean, layered, testable core.

Run from source

git clone https://github.com/<owner>/lambda-logs-viewer
cd lambda-logs-viewer
npm install
npm run dev        # dev server with HMR (default http://localhost:3000)

Production build:

npm run build      # react-router build
npm start          # serve the built app

Checks

npm run typecheck  # react-router typegen + tsc
npm test           # vitest (domain + services)
npm run lint       # Biome (lint + format check)
npm run lint:fix   # Biome (apply fixes)

Please keep typecheck, test and lint green in pull requests.

Project layout

app/
  domain/       # pure entities + log parsing (no I/O, no AWS, no React) - unit-tested
  services/     # use cases, depend on provider interfaces (injected, fakeable)
  infra/aws/    # AWS providers (Lambda / CloudWatch / STS), server-only (*.server.ts)
  routes/       # page routes (loaders) + resource routes (/api/*)
  query/        # TanStack Query keys + hooks
  components/   # presentational UI
  config/       # env.server.ts (dotenv)

The domain layer depends on nothing technical. Services depend on abstractions and receive concrete AWS providers from a single container resolved at startup, so they can be unit-tested with fakes. Credentials and the AWS SDK are confined to *.server.ts and never reach the browser bundle.

License

MIT - see LICENSE.