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

With destructiveHint=true already declared, the description adds a real constraint beyond the schema ('min 1 minute') and the Paymo endpoint. However, it never states that this creates a new record, who may log for whom (the user_id default only appears in the schema), or that no edit path exists here. Useful but not rich behavioral context.

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 action and input shapes, followed by the alternative tool and endpoint reference. No filler and nothing repeated from the schema.

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-param create tool with full schema coverage and no output schema, the description covers what the tool does, the two valid input modes, and the sibling to use instead. Return-value detail is not required here, so nothing essential 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 description coverage is 100%, so baseline would be 3, but the description adds the mutual-exclusivity contract that the schema only implies: date pairs with duration_seconds, start_time pairs with end_time. That is genuine semantic value the agent cannot infer from field descriptions alone.

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 immediately disambiguates from the nearest sibling by naming paymo_start_timer for live timers. An agent can distinguish it from paymo_list_time_entries and paymo_update_time_entry by the word 'log' plus 'completed'.

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?

Explicitly routes to paymo_start_timer when the user wants a live timer and gives the two accepted input shapes for a completed entry. It does not mention paymo_update_time_entry as the correction path, so coverage of alternatives is good but not exhaustive.

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