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

Annotations already include destructiveHint=true, and the description adds that this is a PATCH request and 'Only the fields you provide are changed,' which explains the partial-update behavior. This is valuable context beyond the annotation, though it does not disclose side effects like permission requirements or whether updates are reversible.

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?

The description consists of four short, purposeful sentences: action, partial-update behavior, REST endpoint, and write nature. It is front-loaded with the primary purpose and contains no redundant content.

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?

While the schema documents all parameters and the annotation flags destructiveness, the description does not mention the response format (no output schema) or any operational constraints (e.g., updating a running entry). This leaves gaps for a tool with 8 parameters and no output schema documentation, making it adequate but not fully 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?

The schema has 100% description coverage for all 8 parameters, so the baseline is 3. The description's enumeration of fields ('hours, notes, spent date, or project/task') merely paraphrases the schema and does not add deeper semantics such as mutual exclusivity or formatting constraints beyond what the schema already provides.

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?

The description states a specific verb ('Update') and resource ('existing time entry'), and lists the updatable fields ('hours, notes, spent date, or project/task'). This clearly differentiates it from siblings like create or delete, which are 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?

The description says 'Update an existing time entry,' which implies use for existing entries, but it does not explicitly contrast with alternatives such as harvest_create_time_entry, harvest_restart_time_entry, or harvest_stop_time_entry. The partial-update note provides context, but no explicit when-not-to-use guidance.

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