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

Annotations already declare destructiveHint=true, so the mutation risk is signaled in structured data. The description adds the entry-type model (date+duration vs start/end) and the endpoint mapping (PUT /api/entries/{id}), which is useful context. It does not disclose partial-update semantics, permissions, or whether unspecified fields are cleared — meaningful gaps for a mutation with no output schema.

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 verb and editable fields, then the one constraint that would actually cause a bad call. The endpoint reference is short and earns its place. No filler.

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 mutation with only one required field, no output schema, and annotations limited to destructiveHint, the description covers the core editing model but leaves the update semantics ambiguous — PUT suggests replacement, yet the agent cannot tell whether omitted fields are preserved or cleared. Adequate but not complete.

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 every parameter, including the entry-type restrictions. The description's only marginal addition is the cross-reference telling the agent to use end_time rather than duration_seconds for start/end entries. Baseline 3 applies where the schema does the heavy lifting.

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+resource ('Edit a time entry') and enumerates the editable surface (description, task, length), so an agent can distinguish it from paymo_create_time_entry, paymo_list_time_entries, and paymo_update_task. It does not name a sibling to route against, but the verb/resource pairing is unambiguous.

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 an explicit conditional: duration_seconds applies only to date+duration entries, and for start/end entries the agent should change end_time instead. That is real when-to-use guidance inside the tool's own parameter space. It stops short of stating when to prefer this tool over siblings or what prerequisites exist (e.g., entry ownership).

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