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FastBill MCP by usefulapi

io.usefulapi/fastbillusefulapi.iostreamable-httpv1.0.0Scanned

Read FastBill customers, invoices, estimates, expenses; create customers, invoices, projects.

22 tools: 3 can delete or cancel things, 6 change things and 13 only read.

Tools: 3 delete, 0 irreversible, 6 write, 13 read.
  • Reads private data · 5
  • Reads text others write · 22
  • Can send data out · 1
  • No findings

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9 of these tools change something. Run those as governed actions.

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Tools

Grouped by what each tool does, most consequential first. Open one for its reasons and full description; descriptions are the publisher's own words.

22 tools

Deletes or cancels 3Claude Code: deny
  • fastbill_complete_invoiceWRITE, NOT REVERSIBLE: turn a draft invoice into a final invoice.Reads text others writeNo findings

    Why it is in this group

    • The description's first verb is "write": a word for a change.
    • The server marks it destructive (destructiveHint: true).

    What it can reach

    • untrusted-inputThe server marks it openWorldHint: true: it reaches things outside the server's own data.
    Description, as the server wrote it
    WRITE, NOT REVERSIBLE: turn a draft invoice into a final invoice. FastBill assigns the invoice number and PDF; a final invoice can no longer be edited (it can only be canceled in FastBill). Nothing is sent to the customer. Only call this after the user confirmed the draft. invoice.complete.

    Annotations the server declares

    • title: Finalize invoice
    • readOnlyHint: false
    • destructiveHint: true
    • idempotentHint: false
    • openWorldHint: true
  • fastbill_set_invoice_paidWRITE: mark a final invoice as paid, with the payment date and method.Reads text others writeNo findings

    Why it is in this group

    • The name "fastbill_set_invoice_paid" says "set": a word for a change.
    • The server marks it destructive (destructiveHint: true).

    What it can reach

    • untrusted-inputThe server marks it openWorldHint: true: it reaches things outside the server's own data.
    Description, as the server wrote it
    WRITE: mark a final invoice as paid, with the payment date and method. invoice.setpaid.

    Annotations the server declares

    • title: Mark invoice paid
    • readOnlyHint: false
    • destructiveHint: true
    • idempotentHint: true
    • openWorldHint: true
  • fastbill_update_customerWRITE: update fields of an existing customer; only the fields you pass change.Reads text others writeNo findings

    Why it is in this group

    • The name "fastbill_update_customer" says "update": a word for a change.
    • The server marks it destructive (destructiveHint: true).

    What it can reach

    • untrusted-inputThe server marks it openWorldHint: true: it reaches things outside the server's own data.
    Description, as the server wrote it
    WRITE: update fields of an existing customer; only the fields you pass change. Bank details are not accepted by this tool. customer.update.

    Annotations the server declares

    • title: Update customer
    • readOnlyHint: false
    • destructiveHint: true
    • idempotentHint: true
    • openWorldHint: true
Changes things 6Claude Code: ask
  • fastbill_create_articleWRITE: create a product or service (article number, title and unit price are required).Reads text others writeNo findings

    Why it is in this group

    • The name "fastbill_create_article" says "create": a word for a change.

    What it can reach

    • untrusted-inputThe server marks it openWorldHint: true: it reaches things outside the server's own data.
    Description, as the server wrote it
    WRITE: create a product or service (article number, title and unit price are required). article.create.

    Annotations the server declares

    • title: Create product
    • readOnlyHint: false
    • destructiveHint: false
    • idempotentHint: false
    • openWorldHint: true
  • fastbill_create_customerWRITE: create a customer.Reads text others writeCan send data outNo findings

    Why it is in this group

    • The name "fastbill_create_customer" says "create": a word for a change.

    What it can reach

    • untrusted-inputThe server marks it openWorldHint: true: it reaches things outside the server's own data.
    • outboundThe input takes a destination (input.phone): what the tool writes goes there.
    Description, as the server wrote it
    WRITE: create a customer. customer_type is required; a business needs organization, a consumer needs last_name. Bank details are not accepted by this tool. FastBill does not check for duplicates, so search with fastbill_list_customers first. customer.create.

    Annotations the server declares

    • title: Create customer
    • readOnlyHint: false
    • destructiveHint: false
    • idempotentHint: false
    • openWorldHint: true
  • fastbill_create_estimateWRITE: create an estimate (quote) for a customer from line items.Reads text others writeNo findings

    Why it is in this group

    • The name "fastbill_create_estimate" says "create": a word for a change.

    What it can reach

    • untrusted-inputThe server marks it openWorldHint: true: it reaches things outside the server's own data.
    Description, as the server wrote it
    WRITE: create an estimate (quote) for a customer from line items. It is not sent. estimate.create.

    Annotations the server declares

    • title: Create estimate
    • readOnlyHint: false
    • destructiveHint: false
    • idempotentHint: false
    • openWorldHint: true
  • fastbill_create_invoiceWRITE: create an invoice for a customer from line items.Reads text others writeNo findings

    Why it is in this group

    • The name "fastbill_create_invoice" says "create": a word for a change.

    What it can reach

    • untrusted-inputThe server marks it openWorldHint: true: it reaches things outside the server's own data.
    Description, as the server wrote it
    WRITE: create an invoice for a customer from line items. FastBill stores it as a draft; it gets its number and becomes final only with fastbill_complete_invoice, and it is never sent by this tool. Check the result with fastbill_get_invoice. invoice.create.

    Annotations the server declares

    • title: Create invoice
    • readOnlyHint: false
    • destructiveHint: false
    • idempotentHint: false
    • openWorldHint: true
  • fastbill_create_projectWRITE: create a project for a customer (name and customer are required).Reads text others writeNo findings

    Why it is in this group

    • The name "fastbill_create_project" says "create": a word for a change.

    What it can reach

    • untrusted-inputThe server marks it openWorldHint: true: it reaches things outside the server's own data.
    Description, as the server wrote it
    WRITE: create a project for a customer (name and customer are required). project.create.

    Annotations the server declares

    • title: Create project
    • readOnlyHint: false
    • destructiveHint: false
    • idempotentHint: false
    • openWorldHint: true
  • fastbill_create_time_entryWRITE: book a work time entry on a project (customer, project and start time are required).Reads text others writeNo findings

    Why it is in this group

    • The name "fastbill_create_time_entry" says "create": a word for a change.

    What it can reach

    • untrusted-inputThe server marks it openWorldHint: true: it reaches things outside the server's own data.
    Description, as the server wrote it
    WRITE: book a work time entry on a project (customer, project and start time are required). time.create.

    Annotations the server declares

    • title: Create time entry
    • readOnlyHint: false
    • destructiveHint: false
    • idempotentHint: false
    • openWorldHint: true
Only reads 13Show 13 read-only tools
  • fastbill_get_customerOne customer by FastBill customer id.Reads text others writeNo findings

    Why it is in this group

    • The name "fastbill_get_customer" says "get": a word for reading.

    What it can reach

    • untrusted-inputThe server marks it openWorldHint: true: it reaches things outside the server's own data.
    Description, as the server wrote it
    One customer by FastBill customer id. customer.get with CUSTOMER_ID.

    Annotations the server declares

    • title: Get customer
    • readOnlyHint: true
    • destructiveHint: false
    • openWorldHint: true
  • fastbill_get_invoiceOne invoice by FastBill invoice id, with all line items, VAT, payments and the document URL.Reads private dataReads text others writeNo findings

    Why it is in this group

    • The name "fastbill_get_invoice" says "get": a word for reading.

    What it can reach

    • private-dataThe description's first sentence says "document": it reads documents.
    • untrusted-inputThe server marks it openWorldHint: true: it reaches things outside the server's own data.
    • untrusted-inputThe description's first sentence says "url": it reads web pages, which anyone can write.
    Description, as the server wrote it
    One invoice by FastBill invoice id, with all line items, VAT, payments and the document URL. invoice.get with INVOICE_ID.

    Annotations the server declares

    • title: Get invoice
    • readOnlyHint: true
    • destructiveHint: false
    • openWorldHint: true
  • fastbill_list_articlesList products and services (article number, type, title, unit price, VAT, unit).Reads text others writeNo findings

    Why it is in this group

    • The name "fastbill_list_articles" says "list": a word for reading.

    What it can reach

    • untrusted-inputThe server marks it openWorldHint: true: it reaches things outside the server's own data.
    Description, as the server wrote it
    List products and services (article number, type, title, unit price, VAT, unit). article.get.

    Annotations the server declares

    • title: List products
    • readOnlyHint: true
    • destructiveHint: false
    • openWorldHint: true
  • fastbill_list_contactsList contact persons of customers (name, position, e-mail, phone).Reads private dataReads text others writeNo findings

    Why it is in this group

    • The name "fastbill_list_contacts" says "list": a word for reading.

    What it can reach

    • private-dataThe name "fastbill_list_contacts" says "list" and "contact": it reads contacts.
    • private-dataThe description's first sentence says "list" and "contact": it reads contacts.
    • untrusted-inputThe server marks it openWorldHint: true: it reaches things outside the server's own data.
    • untrusted-inputThe description's first sentence says "list" and "mail": it reads inbound email, which other people can write.
    Description, as the server wrote it
    List contact persons of customers (name, position, e-mail, phone). Filter by customer, search term or contact id. contact.get.

    Annotations the server declares

    • title: List contacts
    • readOnlyHint: true
    • destructiveHint: false
    • openWorldHint: true
  • fastbill_list_customersList customers (name, address, e-mail, VAT id, payment terms and bank details as stored in FastBill).Reads private dataReads text others writeNo findings

    Why it is in this group

    • The name "fastbill_list_customers" says "list": a word for reading.

    What it can reach

    • private-dataThe description's first sentence says "list" and "mail": it reads mail.
    • untrusted-inputThe server marks it openWorldHint: true: it reaches things outside the server's own data.
    • untrusted-inputThe description's first sentence says "list" and "mail": it reads inbound email, which other people can write.
    Description, as the server wrote it
    List customers (name, address, e-mail, VAT id, payment terms and bank details as stored in FastBill). Filter by search term (organization, name, address, zip, e-mail or tags), customer number, country or city. customer.get.

    Annotations the server declares

    • title: List customers
    • readOnlyHint: true
    • destructiveHint: false
    • openWorldHint: true
  • fastbill_list_estimatesList estimates (quotes) with state (a created, b sent, c negotiation, d accepted, e rejected, f invoiced), totals and items.Reads text others writeNo findings

    Why it is in this group

    • The name "fastbill_list_estimates" says "list": a word for reading.

    What it can reach

    • untrusted-inputThe server marks it openWorldHint: true: it reaches things outside the server's own data.
    Description, as the server wrote it
    List estimates (quotes) with state (a created, b sent, c negotiation, d accepted, e rejected, f invoiced), totals and items. estimate.get.

    Annotations the server declares

    • title: List estimates
    • readOnlyHint: true
    • destructiveHint: false
    • openWorldHint: true
  • fastbill_list_expensesList expense entries (supplier, category, net/VAT/gross, dates, document URL).Reads private dataReads text others writeNo findings

    Why it is in this group

    • The name "fastbill_list_expenses" says "list": a word for reading.

    What it can reach

    • private-dataThe description's first sentence says "list" and "document": it reads documents.
    • untrusted-inputThe server marks it openWorldHint: true: it reaches things outside the server's own data.
    • untrusted-inputThe description's first sentence says "list" and "url": it reads web pages, which anyone can write.
    Description, as the server wrote it
    List expense entries (supplier, category, net/VAT/gross, dates, document URL). Filter by invoice number or date ranges. expense.get.

    Annotations the server declares

    • title: List expenses
    • readOnlyHint: true
    • destructiveHint: false
    • openWorldHint: true
  • fastbill_list_invoicesList outgoing invoices, drafts and credit notes with totals, state (draft, unpaid, overdue, paid, canceled), dates and line items.Reads private dataReads text others writeNo findings

    Why it is in this group

    • The name "fastbill_list_invoices" says "list": a word for reading.

    What it can reach

    • private-dataThe description's first sentence says "list" and "note": it reads notes.
    • untrusted-inputThe server marks it openWorldHint: true: it reaches things outside the server's own data.
    Description, as the server wrote it
    List outgoing invoices, drafts and credit notes with totals, state (draft, unpaid, overdue, paid, canceled), dates and line items. Filter by customer, number, type, date ranges (invoice date, due date, paid date, last update). invoice.get.

    Annotations the server declares

    • title: List invoices
    • readOnlyHint: true
    • destructiveHint: false
    • openWorldHint: true
  • fastbill_list_projectsList projects (name, customer, hourly rate, VAT, start/end date).Reads text others writeNo findings

    Why it is in this group

    • The name "fastbill_list_projects" says "list": a word for reading.

    What it can reach

    • untrusted-inputThe server marks it openWorldHint: true: it reaches things outside the server's own data.
    Description, as the server wrote it
    List projects (name, customer, hourly rate, VAT, start/end date). project.get.

    Annotations the server declares

    • title: List projects
    • readOnlyHint: true
    • destructiveHint: false
    • openWorldHint: true
  • fastbill_list_recurring_invoicesList recurring invoice templates (customer, interval data, totals, items).Reads text others writeNo findings

    Why it is in this group

    • The name "fastbill_list_recurring_invoices" says "list": a word for reading.

    What it can reach

    • untrusted-inputThe server marks it openWorldHint: true: it reaches things outside the server's own data.
    Description, as the server wrote it
    List recurring invoice templates (customer, interval data, totals, items). recurring.get.

    Annotations the server declares

    • title: List recurring invoices
    • readOnlyHint: true
    • destructiveHint: false
    • openWorldHint: true
  • fastbill_list_revenuesList revenue entries (income booked in FastBill: customer, totals, dates, payments).Reads text others writeNo findings

    Why it is in this group

    • The name "fastbill_list_revenues" says "list": a word for reading.

    What it can reach

    • untrusted-inputThe server marks it openWorldHint: true: it reaches things outside the server's own data.
    Description, as the server wrote it
    List revenue entries (income booked in FastBill: customer, totals, dates, payments). Takes the same filters as invoices. revenue.get.

    Annotations the server declares

    • title: List revenues
    • readOnlyHint: true
    • destructiveHint: false
    • openWorldHint: true
  • fastbill_list_templatesList the invoice/estimate templates (template id, name, hash).Reads text others writeNo findings

    Why it is in this group

    • The name "fastbill_list_templates" says "list": a word for reading.

    What it can reach

    • untrusted-inputThe server marks it openWorldHint: true: it reaches things outside the server's own data.
    Description, as the server wrote it
    List the invoice/estimate templates (template id, name, hash). Use a template id with the create tools. Ids change whenever a template is edited. template.get.

    Annotations the server declares

    • title: List document templates
    • readOnlyHint: true
    • destructiveHint: false
    • openWorldHint: true
  • fastbill_list_time_entriesList work time entries (customer, project, date, minutes, billable minutes, comment, invoice).Reads text others writeNo findings

    Why it is in this group

    • The name "fastbill_list_time_entries" says "list": a word for reading.

    What it can reach

    • untrusted-inputThe server marks it openWorldHint: true: it reaches things outside the server's own data.
    • untrusted-inputThe description's first sentence says "list" and "comment": it reads comments, which other people can write.
    Description, as the server wrote it
    List work time entries (customer, project, date, minutes, billable minutes, comment, invoice). Without filters FastBill returns the latest entries of the current month. time.get.

    Annotations the server declares

    • title: List time entries
    • readOnlyHint: true
    • destructiveHint: false
    • openWorldHint: true

This is not a safety rating, and no finding is not a safety guarantee. The groups and findings come from fixed checks of the tool definitions the server returned on the date shown, not from its code or what it does when called. How the checks work.

Exfil surface

Which tools read private data, which read text someone else can write, and which can send data out. One of each is a path a prompt injection can use.

110 paths in this server alone from private data, through text someone else wrote, to a way out. Denying 1 outbound tool breaks every one.

Reads private data5
Reads files, mail, messages, databases, secrets, calendars or repositories.
Reads text others write22
Brings in text someone else can write: web pages, inbound email, messages, issues and comments.
Can send data out1
Can carry data to people or systems: it sends, posts or publishes, or takes a recipient, channel or URL.
deny to break every path
{
  "permissions": {
    "deny": [
      "mcp__fastbill__fastbill_create_customer"
    ]
  }
}

Other servers in the same agent add their own tools to these paths. Audit your whole setup to see them together.

Findings

Matches of fixed checks, with the text they matched.

No check matched anything in these tool definitions. That is not a safety guarantee.

History

Changes to its tool definitions and to its remote endpoint, newest first.

No change seen yet. Its tools are rescanned every day, and a remote endpoint is looked at once a week.

All changes to this server

Install

Pinned to version 1.0.0. Values in angle brackets are yours to fill in.

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

Run in a terminal.

Claude Code permissions

Allow the reads, ask before a change or a way out, deny the deletes. Paste into .claude/settings.json.

.claude/settings.json
{
  "permissions": {
    "allow": [
      "mcp__fastbill__fastbill_list_customers",
      "mcp__fastbill__fastbill_get_customer",
      "mcp__fastbill__fastbill_list_contacts",
      "mcp__fastbill__fastbill_list_invoices",
      "mcp__fastbill__fastbill_get_invoice",
      "mcp__fastbill__fastbill_list_recurring_invoices",
      "mcp__fastbill__fastbill_list_estimates",
      "mcp__fastbill__fastbill_list_expenses",
      "mcp__fastbill__fastbill_list_revenues",
      "mcp__fastbill__fastbill_list_articles",
      "mcp__fastbill__fastbill_list_projects",
      "mcp__fastbill__fastbill_list_time_entries",
      "mcp__fastbill__fastbill_list_templates"
    ],
    "ask": [
      "mcp__fastbill__fastbill_create_customer",
      "mcp__fastbill__fastbill_create_invoice",
      "mcp__fastbill__fastbill_create_estimate",
      "mcp__fastbill__fastbill_create_article",
      "mcp__fastbill__fastbill_create_project",
      "mcp__fastbill__fastbill_create_time_entry"
    ],
    "deny": [
      "mcp__fastbill__fastbill_update_customer",
      "mcp__fastbill__fastbill_complete_invoice",
      "mcp__fastbill__fastbill_set_invoice_paid"
    ]
  }
}

Tools that only read are allowed, tools that change things ask first, tools that delete or cancel are denied. A read that can send data out (it takes a URL, say) asks first too. It assumes the server is installed as fastbill. Review it before you use it.

Capability tags behind 22 rules
  • mcp__fastbill__fastbill_list_customers private-data, untrusted-input
  • mcp__fastbill__fastbill_get_customer untrusted-input
  • mcp__fastbill__fastbill_list_contacts private-data, untrusted-input
  • mcp__fastbill__fastbill_list_invoices private-data, untrusted-input
  • mcp__fastbill__fastbill_get_invoice private-data, untrusted-input
  • mcp__fastbill__fastbill_list_recurring_invoices untrusted-input
  • mcp__fastbill__fastbill_list_estimates untrusted-input
  • mcp__fastbill__fastbill_list_expenses private-data, untrusted-input
  • mcp__fastbill__fastbill_list_revenues untrusted-input
  • mcp__fastbill__fastbill_list_articles untrusted-input
  • mcp__fastbill__fastbill_list_projects untrusted-input
  • mcp__fastbill__fastbill_list_time_entries untrusted-input
  • mcp__fastbill__fastbill_list_templates untrusted-input
  • mcp__fastbill__fastbill_create_customer untrusted-input, outbound
  • mcp__fastbill__fastbill_update_customer untrusted-input
  • mcp__fastbill__fastbill_create_invoice untrusted-input
  • mcp__fastbill__fastbill_complete_invoice untrusted-input
  • mcp__fastbill__fastbill_set_invoice_paid untrusted-input
  • mcp__fastbill__fastbill_create_estimate untrusted-input
  • mcp__fastbill__fastbill_create_article untrusted-input
  • mcp__fastbill__fastbill_create_project untrusted-input
  • mcp__fastbill__fastbill_create_time_entry untrusted-input

Pin

Keep the decision: fail CI when the tools change, follow every change, or show a badge.

Pin in CI

Fail a build when the tools you reviewed are not the tools the server serves today.

curl -s "https://anlyon.dev/api/v1/servers/io.usefulapi/fastbill/verify?hash=caae121d09fb81fc79410b3440d1af6811c951200446370abff38523f2aa59ea" | jq -e '.changed == false'

Pinned hash caae121d09fb, from Oct 26, 2026, 00:25 UTC.

Watch

Get told when its tools change: a new tool, a new description, a new class.

https://anlyon.dev/servers/io.usefulapi/fastbill/changes.xml

An Atom feed. Works in any feed reader or Slack's RSS app.

Badge

anlyon.dev badge for io.usefulapi/fastbill
[![anlyon.dev](https://anlyon.dev/badge/io.usefulapi/fastbill.svg)](https://anlyon.dev/servers/io.usefulapi/fastbill)

Source: MCP Registry · repository. Synced Oct 26, 2026, 00:25 UTC.