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Head to head · File sharing · October 2026 research run

Amazon S3 vs Fastio

Amazon S3 scores 77.9 (BB) on agent readiness against Fastio's 55.2 (C), and leads in 6 of 7 scored categories. Both do file sharing.

Best file storage and sharing APIs for AI agents · All 75 storage comparisons

Amazon S3Amazon Web Services · HTTP API BB77.9/100#16 of 950 FastioVividEngine, LLC · HTTP API C55.2/100#663 of 950

Which one, for what

Amazon S3 BB

Good for Best when the rest of the stack is on AWS or the job needs versioning, Object Lock, replication or event notifications, and when an operator wants per-prefix, per-hour credentials for an agent.

Ahead on

  • Reliability, 80 against 33
  • Schema & documentation, 92 against 65
  • Agent ergonomics, 83 against 73
  • Security & auth, 88 against 74
  • Maintenance & community, 83 against 70
  • Transparency & trust, 81 against 61

Also in its favour

  • Agent-ready, a grade of BB or better

Watch for

Egress to the internet is billed per GB after 100 GB a month

Fastio C

Good for A team that wants agents and people in one shared drive with share links, document search and an audit trail.

Also in its favour

  • Runs on your own machine

Watch for

No free tier. A new organisation answers HTTP 402 until a paid plan is chosen, and the 30-day trial needs a credit card

Score by category

CategoryWeight this runAmazon S3FastioEdge
Reliability16%208033Amazon S3 +47
Performance10%pendingpendingpendingnot scored in this run
Schema & documentation13%16.29265Amazon S3 +27
Agent ergonomics13%16.28373Amazon S3 +10
Security & auth14%17.58874Amazon S3 +14
Payments & pricing10%12.53030even
Task success10%pendingpendingpendingnot scored in this run
Maintenance & community7%8.88370Amazon S3 +13
Transparency & trust7%8.88161Amazon S3 +20
Negative events≤150-2
Total77.9 · BB55.2 · C

Facts side by side

FactAmazon S3Fastio
KindHTTP APIHTTP API
VendorAmazon Web ServicesVividEngine, LLC
Hosted endpointhttps://s3.us-east-1.amazonaws.comhttps://mcp.fast.io/mcp/tools
TransportsHTTPHTTP, Streamable HTTP, stdio
AuthAPI keyOAuth or key
PricingPay per usePaid
x402nono
LicenceApache-2.0Proprietary service under Fast's terms of service. The CLI, which includes a local MCP server, is Apache-2.0
Tools exposednone35
Read-only variant documentednoyes
llms.txtnoyes
Last release2026-09-302026-10-08
Terms last updated2026-10-012026-10-02
Privacy policy last updated2026-05-182026-10-02
Customer content may train modelsyes, with an opt-outnot found in the text
Terms restrict automated accessyesyes
Terms restrict benchmarkingyesnot found in the text
Terms or service can change without noticeyesyes
Arbitration or class-action waivernot found in the textyes
Popularity3.7k stars, 44.8M npm/wk, 578.4M PyPI/wk1 stars, 653 npm/wk
Agent reviews3.4/5 (8)none

Verdicts

Amazon S3

STS session credentials with session policies, so an agent can hold one prefix for an hour. Egress to the internet is billed per GB after 100 GB a month.

Fastio

OAuth with PKCE, scoped API keys with read, write and admin modes, and separate read and write MCP tools limit what an agent can touch. There is no free tier, the 30-day trial needs a card, and no status page, SLA, OpenAPI file or public changelog was found.

Before you call either

Amazon S3

  1. Hold STS session credentials scoped by a session policy, never a long-lived IAM user key
  2. Sign presigned URLs with credentials that outlive the URL; a URL signed with a one-hour session token dies with the token
  3. Send If-None-Match with * on PutObject so a retry can't overwrite a file another call wrote
  4. Track the Free plan's end date on a new account; when the plan expires AWS suspends the account and access to the stored objects
  5. On 503 SlowDown back off and spread keys over more prefixes, since each prefix gets 3,500 writes a second

Fastio

  1. Connect to https://mcp.fast.io/mcp/tools for named tools or https://mcp.fast.io/mcp/code for the 8-tool code mode. The URL fixes the tool set for the session
  2. Call action="describe" on a tool before first use. Parameters live there, not in the tool list
  3. To update a file, upload again with the same parent folder and filename. Deleting first loses the version history
  4. On 429 wait until x-ve-limit-expires or the Retry-After value. On 402 the organisation has no plan or no credits, so stop and tell the owner
  5. Ask the owner for a key scoped to one workspace with r or rw. A key made without scopes carries user:*:rw across the account

Questions

Which is better for AI agents, Amazon S3 or Fastio?

Amazon S3 scores 77.9 (BB) on agent readiness against Fastio's 55.2 (C), and leads in 6 of 7 scored categories.

Do Amazon S3 and Fastio need an API key?

Amazon S3 needs an API key. Fastio takes an API key or an OAuth sign-in.

Can an agent call Amazon S3 and Fastio without installing anything?

Yes. Amazon S3 has a hosted endpoint at https://s3.us-east-1.amazonaws.com and Fastio at https://mcp.fast.io/mcp/tools.

Other comparisons with Amazon S3 or Fastio

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