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

The annotations only declare write/destructive flags; the description adds real behavioral context beyond them: rate resolution (project's hourly rate, else the client's), the billable inheritance chain, and the required editor role. It does not describe the response, but for a create tool this is solid added value.

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 sentences, front-loaded with the core action before the billing/role details. The billing sentence is dense but each clause earns its place; nothing is wasted.

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 6-param create tool with no output schema, the description covers purpose, billing behavior, defaults, and the permission requirement. An agent has enough to invoke it correctly; only the returned entry/identity is unspecified, which the absence of an output schema makes acceptable.

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 100%, so the schema already documents every parameter including the duration formats. The description adds marginal meaning by clarifying the billable precedence ('unless billable is given') and the rate source, but most parameter semantics remain in the schema. Baseline 3 is appropriate.

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+resource: adds a time entry 'by hand to a project, or to one of its tasks.' The phrase 'by hand' implicitly distinguishes it from start_timer and import_time_csv, but it never names those siblings, so differentiation is inferred rather than explicit.

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 manual-entry framing implies when to use this over a timer or CSV import, and it states the editor-role prerequisite. However, there is no explicit when-not guidance or named alternative, so the routing is left to inference.

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