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

The description adds meaningful behavioral context beyond the annotations: it clarifies partial-update semantics, case-insensitive status handling, the budget side effect of cost adjustments, and how markup determines client pass-through. These details help the agent understand what will happen when the tool is invoked, which is especially valuable since the annotations are minimal.

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?

The description is compact, front-loaded with the purpose, and every sentence delivers actionable information: what is updated, how updates behave, and key side effects. No filler or redundancy is present.

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?

The description covers the most important behavioral nuances and side effects, but the tool has 10 parameters with no parameter-level schema descriptions and no output schema. An agent would still lack clarity on several parameter meanings and on what the tool returns after a successful update, so the context is adequate but not complete.

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?

With 0% schema description coverage, the description must compensate for the 10 parameters, but it only adds meaning for status, budgeted_cost, and markup_percentage. Parameters such as name, notes, agreement, assignee_id, is_billable, spent_to_date, and external_service_id receive no explanation beyond their schema type, leaving a significant semantic gap.

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?

The description clearly identifies a specific verb ('Update') and resource ('an external or subcontractor service line'), making the tool's primary purpose obvious. It does not explicitly contrast itself with sibling tools like projects_create_external_service or projects_delete_external_service, but the resource and action are distinct enough for an agent to select it correctly.

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?

The description gives concrete usage context: only passed fields are changed, status is case-insensitive with an enumerated set of values, and cost changes affect the project budget. It stops short of stating when not to use this tool versus alternatives, but the partial-update behavior and side-effect warnings provide clear guidance for correct invocation.

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