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

Annotations only declare destructiveHint=true; the description adds meaningful behavior: end_time defaults to now, the resulting duration must be >= 1 minute, and the underlying PUT /api/entries/{id}. It doesn't say what happens if the timer is already stopped or whether end_time can be set in the past, which keeps it from a 5.

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: action, constraint, discovery step, and endpoint. Zero filler and the core behavior 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?

With no output schema, the description covers the key operational facts (default end_time, duration floor, how to obtain entry_id). It stops short of describing server responses or error cases for an already-stopped timer, which an agent might want.

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 non-obvious default (now) and the minimum-duration constraint that governs the end_time value. The description field's role on a stop operation is still unexplained.

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 ('Stop a running timer by setting its end_time') and implicitly distinguishes itself from paymo_start_timer and paymo_update_time_entry. An agent can tell immediately what this mutates and how.

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 a concrete prerequisite path: find the running entry via paymo_list_time_entries with running_only=true, and states the constraint that final duration must be at least 1 minute. It does not explicitly say when not to use it (e.g., versus editing an already-stopped entry), so it falls short of a 5.

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