Amazon S3 vs Box API + MCP

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.

Box API + MCP

Public OpenAPI 3.0 spec with 297 operations, year-based API versions and an llms.txt of Markdown pages. 20 status-feed entries between 7 July and 1 October 2026, two of them over two hours on uploads or multiple services.

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. Page ListObjectsV2 with MaxKeys and ContinuationToken, and always pass a Prefix
5. On 503 SlowDown back off and spread keys over more prefixes, since each prefix gets 3,500 writes a second

Box API + MCP

1. Call who_am_i first; the tool list depends on the plan, the admin's toggles and the scopes granted
2. Expect download and upload URL, move and shared-link tools to be missing unless an admin has enabled them
3. Pass fields= to trim responses and page folder listings with limit and marker
4. Send a box-version header to pin an API version, and watch responses for a Deprecation header
5. For a link that expires, set shared_link.unshared_at on a paid account; the free plan can't