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File uploads: S3 presigned URLs, validation and the real cost of storage

Receive files without routing them through your server or blowing up storage costs

Data reviewed on Sep 8, 2026 · LLM Stats indexes and official prices

The data, today

The context

Receiving files looks simple until 2 GB videos arrive. Routing every upload through your server consumes bandwidth, memory and request time. The usual pattern is for the server to issue a short-lived presigned URL and for the browser to upload straight to object storage; your server only authorizes and records.

The other side is cost. Storage is paid per GB per month, but also per request and, above all, for the data transferred out when serving it. Before choosing a provider, estimate all three with your real pattern. Codifly's storage catalog and real-cost guide start from official rates.

What to decide

  1. 1

    Upload through my server or with a presigned URL?

    With a presigned URL: the server validates who is uploading, what type and what maximum size, and issues a URL that expires in minutes. The file never passes through your infrastructure. For large files, use multipart upload.

  2. 2

    What do I validate, and when?

    Before signing, validate the user, declared type and maximum size. After the upload, check the actual content, because the declared type can be forged, and scan the file if it will be served to other users. Store under names you generate, not the user's.

  3. 3

    What does it really cost?

    Add three parts: GB stored per month, read and write requests, and data transferred out. Egress is the one that surprises you when files are served heavily. Compare providers in the storage catalog with your volume, not on price per GB alone.

Common mistakes

  • Routing every file through your application server.
  • Trusting the MIME type or extension the client declares.
  • Comparing providers on price per GB alone without counting egress.

Tools and comparators

AWS savings calculatorObject storage comparatorCloud options comparator

Guides to go deeper

Want a recommendation for your case?

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No provider pays for its position. Indexes come from LLM Stats; prices from each provider's standard API. How we measure

Reduce AI costsMeasure tokens per request and pay for big models only when neededAI customer supportWork out cost per conversation without dropping below your quality barDocument search and RAGFind the right passage before asking the model for an answerCoding with AIMeasure cost per coding task and review what the agent writesCut cloud costsFind the hidden spend in egress, operations and idle resourcesHandle traffic spikesAbsorb traffic bursts without dropping requests or the databaseShip to productionDeploy from Git with separate environments and clean configurationChoose a databaseCompare Supabase, Neon, Turso, PlanetScale and D1 by how they billLaunch an MVPDeploy and store data at minimum cost and without surprisesEvaluate new AI providersCompare Kimi, GLM, Qwen and Muse Spark with the leadersCI/CD from GitHub to productionShip every commit with tests and no long-lived keys in GitHubSecrets and environmentsSeparate dev, staging and production and stop leaking environment variablesObservability without surprise billsMeasure what matters with OpenTelemetry and SLOs that don't page anyone for nothingQueues and background jobsProcess heavy tasks without duplicates when something retriesInfrastructure as codeDecide between Terraform and OpenTofu and keep your infrastructure in GitFast PostgreSQLFind the slow query with EXPLAIN and fix it with the right indexKubernetes or PaaS?Choose where to run your app based on your team, not on fashion
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