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Sellsy MCP by usefulapi

io.usefulapi/sellsy in the official MCP registry. Endpoint https://sellsy.usefulapi.io/mcp. Source: github.com/m190/usefulapi-mcp.

The registry describes it as: Search and read Sellsy companies, contacts, opportunities, invoices and tasks; create records.

We read its 44 tools on 2026-10-31. 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.

Connect it

The endpoint answers MCP over HTTP; that is how we read it. Add it to your client:

Claude Code

claude mcp add --transport http sellsy https://sellsy.usefulapi.io/mcp

Cursor: ~/.cursor/mcp.json

{
  "mcpServers": {
    "sellsy": {
      "url": "https://sellsy.usefulapi.io/mcp"
    }
  }
}

VS Code

code --add-mcp '{"name":"sellsy","type":"http","url":"https://sellsy.usefulapi.io/mcp"}'

Some servers ask you to sign in the first time a client connects, or want a key from the people who run them; the server's own docs say which.

Let Claude Code check servers as it adds them

With the free lazaretto-guard plugin installed, when Claude Code adds a server for you or writes one into an MCP config, the plugin reads the server's tools first and asks you if one of our rules matches. Install it, restart Claude Code, then ask it to run the command above.

Install lazaretto-guard

claude plugin marketplace add jamesdfinance-dev/lazaretto-plugins
claude plugin install lazaretto-guard@lazaretto-plugins

Tools it advertises

sellsy_search sellsy_list_companies sellsy_search_companies sellsy_get_company sellsy_list_company_contacts sellsy_list_individuals sellsy_search_individuals sellsy_get_individual sellsy_list_contacts sellsy_search_contacts sellsy_get_contact sellsy_list_opportunities sellsy_search_opportunities sellsy_get_opportunity sellsy_list_opportunity_pipelines sellsy_list_pipeline_steps sellsy_list_estimates sellsy_search_estimates sellsy_get_estimate sellsy_list_invoices sellsy_search_invoices sellsy_get_invoice sellsy_list_invoice_payments sellsy_list_orders sellsy_search_orders sellsy_get_order sellsy_list_credit_notes sellsy_get_credit_note sellsy_list_items sellsy_search_items sellsy_get_item sellsy_search_payments sellsy_list_tasks sellsy_search_tasks sellsy_get_task sellsy_list_task_labels sellsy_search_comments sellsy_list_staffs sellsy_create_company sellsy_create_individual sellsy_create_contact sellsy_create_opportunity sellsy_create_comment sellsy_create_task

Tool changes

We compare every full read of this server with the one before. No change in what its tools say has been seen since we started keeping this record on 2026-10-30.

Fingerprint of its tools at our last full read (2026-10-31): eee68ada9f529a7f. A client can hash the tools it is served the same way and compare; the full value and a hash per tool are in this page as JSON.

Run this server? Show the check in your README

The badge reflects the latest weekly read:

Markdown

[![MCP tool check](https://lazaretto.dev/mcp-registry/io-usefulapi-sellsy/badge.svg)](https://lazaretto.dev/mcp-registry/io-usefulapi-sellsy)

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.