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

Annotations already flag write/destructive/idempotent/openWorld, and the description adds genuinely new context: read-modify-write semantics ('reads the cost code first and sends the full object') and partial-update behavior ('only the fields you pass change'). This clarifies that despite destructiveHint, unspecified fields are preserved. No mention of permission requirements or error behavior.

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

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

Two compact sentences, front-loaded with the WRITE marker and partial-update rule, ending with the endpoint. No filler.

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

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

For a mutation tool with no output schema, the description covers safety profile, update semantics, and endpoint. The only real gap is the undocumented 'identifier' parameter and lack of any note on validation errors.

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

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

Schema coverage is 33%, so the description carries real burden. It maps name, cost_type_id, and is_active to their effects, but says nothing about 'identifier', leaving one parameter undocumented in both schema and description; display_option and cost_code_id are covered by the schema itself.

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

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

Opens with an explicit verb+resource ('WRITE: change fields of an existing cost code') and enumerates the concrete field changes (rename, cost type, retire). An agent can distinguish it from exaktime_create_cost_code and exaktime_get_cost_code without inspecting either schema.

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

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

'existing cost code' plus 'set is_active=false to retire it' tells the agent when this applies versus creating a new record. No sibling is named explicitly, and there is no explicit exclusion, so it stops short of a full 5.

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