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

Annotations only declare destructiveHint=true; the description adds real behavioral context: the end_time defaults to now, and the resulting duration must be at least 1 minute — a validation constraint not derivable from the schema. It does not disclose permission/error behavior, so it is good but not exhaustive.

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: the core action and default lead, the constraint follows, then the discovery hint. Zero filler and the most important information is front-loaded.

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?

No output schema exists, but for a simple mutation the description covers the action, the default, the validation constraint, and the endpoint. Minor gaps around error/permission behavior keep it just under full marks.

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 the schema already documents all three parameters including the end_time default. The description restates the now-default and the entry_id meaning without adding format or edge-case detail, so baseline 3 applies.

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 (Stop) and resource (running timer), and the mechanism (setting end_time). It is trivially distinguishable from the sibling paymo_start_timer and from paymo_update_time_entry.

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 the agent to paymo_list_time_entries with running_only=true to locate the target, which is genuine workflow guidance. It stops short of stating exclusions (e.g., what to do if no timer is running, or use of update_time_entry instead), so not a full 5.

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