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erp-mafia

Fortnox MCP Server

by erp-mafia

Update Fortnox Customer

fortnox_update_customer
Idempotent

Update an existing customer in Fortnox using the customer number and optional fields to modify. Returns the updated customer details.

Instructions

Update an existing customer in Fortnox.

Args:

  • customer_number (string): Customer number to update (required)

  • name, email, phone, address fields, etc.: Fields to update (only provided fields are changed)

Returns: The updated customer details.

Input Schema

TableJSON Schema
NameRequiredDescriptionDefault
cityNoCity
nameNoCustomer name
emailNoPrimary email address
phoneNoPrimary phone number
activeNoWhether the customer is active
countryNoCountry name
address1NoStreet address line 1
address2NoStreet address line 2
commentsNoInternal comments
currencyNoCurrency code
zip_codeNoPostal/ZIP code
vat_numberNoVAT registration number
country_codeNoTwo-letter country code
customer_numberYesCustomer number to update (required)
response_formatNoOutput format: 'markdown' or 'json'markdown
terms_of_paymentNoPayment terms code
organisation_numberNoOrganisation/company number
Behavior4/5

Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?

Annotations already indicate mutating (readOnlyHint=false) and non-destructive (destructiveHint=false). The description adds valuable behavioral details: 'only provided fields are changed' conveys partial-update semantics, and 'Returns: The updated customer details' sets expectations. It does not cover error behavior or authorization, but with annotations present this is sufficient.

Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.

Conciseness5/5

Is the description appropriately sized, front-loaded, and free of redundancy?

The description is extremely concise: one opening sentence, a short Args list, and a one-line Returns statement. No wasted words, and the structure is front-loaded with the purpose.

Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.

Completeness4/5

Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?

The tool has many parameters but the schema fully documents each. The description covers purpose, partial-update behavior, and return value. Given the rich schema and annotations, this is adequately complete, though it could mention failure scenarios (e.g., customer not found) for full contextual coverage.

Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.

Parameters4/5

Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?

Schema description coverage is 100%, so baseline is 3. The description adds meaning beyond the schema by explaining that optional fields are updated only when provided (partial update), which is critical for understanding how to use the 17 parameters.

Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.

Purpose5/5

Does the description clearly state what the tool does and how it differs from similar tools?

The description states 'Update an existing customer in Fortnox' with a specific verb and resource, clearly distinguishing it from creation (fortnox_create_customer), deletion (fortnox_delete_customer), and read-only tools (fortnox_get_customer, fortnox_list_customers).

Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.

Usage Guidelines4/5

Does the description explain when to use this tool, when not to, or what alternatives exist?

The phrase 'existing customer' implies this tool is for updating already-created customers and not for creating new ones, providing clear context. However, it does not explicitly name alternative tools or state when not to use it, so it misses the top score.

Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.

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