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Lob MCP by usefulapi
io.usefulapi/lob in the official MCP registry.
Endpoint https://lob.usefulapi.io/mcp. Source: github.com/m190/usefulapi-mcp.
The registry describes it as: Verify US & international addresses and send physical mail (postcards, letters, checks) via Lob.
We read its 18 tools on 2026-10-25. Nothing in them matched our tool-poisoning rules. It also sets server instructions, text a client puts in front of the model on connect; those were read too.
A clean read means these rules found nothing, not that the server is harmless. A server can change its tools at any time, which is why the index reads it again every week.
Tools it advertises
lob_verify_us_address lob_verify_intl_address lob_us_zip_lookup lob_us_autocomplete lob_list_postcards lob_get_postcard lob_list_letters lob_get_letter lob_list_checks lob_get_check lob_list_self_mailers lob_list_addresses lob_get_address lob_list_templates lob_create_address lob_create_postcard lob_create_letter lob_cancel_postcard
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[](https://lazaretto.dev/mcp-registry/io-usefulapi-lob)How this was checked
Lazaretto connects to the endpoint the way any MCP client does, asks the server to introduce itself and list its tools, and reads every name, description, parameter schema and server instruction for tool poisoning: hidden directive blocks, orders to read local secrets, parameters built to carry secrets or the conversation out, orders that redirect another server's tools, and invisible characters. It never calls a tool. What we found across the registry.
To run the same check every time Claude Code adds a server, install the free lazaretto-guard plugin. Browse every server in the index.