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

Annotations only supply destructiveHint=true, so the description carries most of the burden. It usefully adds the either/or input contract and the one-minute minimum, but says nothing about permissions, whether entries can be edited afterward (paymo_update_time_entry exists), or side effects of logging time.

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 tight sentences: capability and validation first, alternative tool second, endpoint last. No filler or repetition of schema details.

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 7-parameter creation tool with no output schema and thin annotations, the description covers the input contract and sibling routing adequately. It omits what the call returns and any post-creation behavior, which would round it out.

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 100%, so the baseline is 3, but the description adds the mutually-exclusive grouping of date+duration_seconds vs start_time+end_time that the flat schema cannot express. That is genuine semantic value beyond the parameter list.

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 ('Log a completed time entry on a task') and explicitly distinguishes itself from the sibling paymo_start_timer, which handles the live-timer case. An agent can pick 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?

Gives the exact input shapes ('EITHER as date + duration_seconds OR as start_time + end_time'), a validation rule (min 1 minute), and names the alternative tool for a different intent. This is near-complete routing guidance.

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