EasyPost vs ShipStation API

EasyPost

Docs written for agents (llms.txt, a Markdown copy of each page, a JSON page index), seven official SDKs and free test keys make the REST API easy to start on. No OpenAPI spec or idempotency keys were found, every key has full account access, and the status page shows a connectivity outage on 23 July 2026 that affected all operations.

ShipStation API

A public OpenAPI 3.1 contract with 173 operations, Markdown docs for agents and a free ShipStation API plan with a sandbox make a first rate quote or test label reachable without a contract. One API key carries full account access, with no scopes, read-only mode or idempotency keys on label purchases.

EasyPost

1. Use a test API key while building. It buys no postage and contacts no carrier, and test tracking codes simulate each tracking status
2. Don't blind-retry POST /shipments/:id/buy after a timeout. Retrieve the shipment first and check for postage_label, since no idempotency key exists
3. Send the API key as the HTTP Basic username with an empty password on the REST API, and as a Bearer token on the MCP server
4. Handle errors as either an array of objects or an array of strings. The docs say both shapes occur
5. Pass a scoped carrier_accounts list when rating. Only the first 60 accounts are rated and the call doesn't fail when more are enabled

ShipStation API

1. Send the key in an API-Key header to https://api.shipstation.com/v2. A key that starts TEST_ runs in the sandbox on the same host
2. Call GET /v2/carriers first. Rate and label calls need carrier_ids or a carrier_id and a service_code from that account
3. Don't blindly retry POST /v2/labels after a timeout. List labels first, then void a duplicate with PUT /v2/labels/{label_id}/void
4. Check the errors array on 2XX responses too, and read error_source to tell a carrier fault from a ShipStation one
5. On a platform (Standard or Premium) key every label is real and charged. Ask the owner before buying, and void test labels at once