create_time_entry_until

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

Annotations already declare mutating, non-idempotent, non-destructive behavior, and the description adds genuinely new context: hours are computed locally and only hours + start_time are submitted because the server rejects end_time, plus the strict end_time > start_time constraint. It stops short of stating permission requirements or what the confirm=false preview returns.

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 core behavior is front-loaded in the first sentence and the constraint follows immediately. The parenthetical cross-reference to create_time_entry's docstring is only mildly wasteful, and every remaining sentence carries behavioral information.

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 9-parameter mutation with no output schema, it covers the non-obvious computation and ordering rules that would otherwise cause failed calls. It leaves the preview-vs-applied result shape and permission prerequisites to the schema's confirm description and annotations.

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 only 33% (9 params, most undocumented), and the description compensates for the critical pair — it explains that end_time is never transmitted and is converted to hours, and that start_time defines the base. However, required parameters activity, spent_on, and the optional user/comment remain unexplained in both places, leaving a real 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?

States a specific verb and resource ('Create a time entry') plus the distinguishing mechanism ('by start/end time instead of a duration'). It explicitly names the sibling it differs from (create_time_entry / ongoing entries), so an agent can route between them without opening 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?

The closing sentence gives a clear selection rule: known end time → this tool, ongoing entry → create_time_entry. It does not address the update counterparts (update_time_entry, update_time_entry_until), so the routing guidance is clear but not exhaustive.

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