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

Annotations only declare the generic mutating profile (readOnly=false, idempotent=false, destructive=false); the description adds non-obvious behavior: the currency must be pre-converted to the project currency, and a SPENT line feeds the project's earned-value actual cost. It also states the exact permission requirement, which annotations do not cover.

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?

Three tight sentences: purpose first, then the currency trap, then the EVM consequence and access rule. Every clause carries information the agent cannot get from the schema or annotations.

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 an 8-parameter, non-idempotent create tool with 88% schema coverage and no output schema, the definition covers the risky unknowns: units, side effects on earned value, and authorization. Nothing important for a correct first call is missing.

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 already 88%, so the baseline is 3; the description adds real meaning on top by explaining the monetary unit of amount and the business meaning of the EXPECTED/COMMITTED/SPENT status values. The date parameter's earned-value effect is only in the schema, so the description does not fully duplicate the value.

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?

States a specific verb and resource ("Add a cost line to a project's budget list") and immediately enumerates the three data dimensions it captures. An agent can tell this is the create-side of the cost-line family versus list_cost_lines or update_cost_line without opening the 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?

Gives clear preconditions in the form of a hard constraint ("There is no currency argument: convert the amount first") plus the authorization rule (project.edit and budget.read). It never names list_cost_lines or update_cost_line as alternatives, so there is no explicit when/when-not routing, which keeps it below a 5.

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