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

Goes well beyond the annotations (readOnlyHint=false, destructiveHint=false, openWorldHint=false) by disclosing execution semantics: the tool runs immediately rather than returning a plan_token, it writes only the caller's own record, the record is undoable, and destructive/outbound/financial actions are handled differently. That is exactly the context an agent needs before invoking a write tool autonomously.

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?

Front-loads the core action and input-mode rules, then the confirmation policy, so the important content comes first. The confirmation paragraph is long relative to the rest of the definition, but each sentence (immediate run, own-record scope, undo path, contrast with destructive/outbound tools) carries distinct information; the parenthetical '(a manual worklog line, not a live stopwatch)' is the only borderline redundancy.

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 zero-required-parameter mutation tool with no output schema and no schema-level parameter descriptions, the definition still supplies input-mode rules, execution/confirmation semantics, and scope of the write. An agent has everything needed to decide to call it and how to shape the arguments.

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?

With 0% schema description coverage the description must carry parameter meaning, and it does: 'minutes' as a positive whole number, started_at/ended_at as ISO 8601, description as free text, task_id as a personal reference. It leaves a gap on precedence — it does not say what happens if both 'minutes' and 'started_at' are supplied, or whether 'ended_at' alone is valid.

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 block of time for the caller') and immediately disambiguates with '(a manual worklog line, not a live stopwatch)', which separates it from logging/listing siblings an agent might otherwise confuse it with.

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 explicit input-mode rules: duration must be given EITHER via 'minutes' OR an explicit started_at/ended_at pair, and 'with minutes and no start, the block ends now'. It also marks description and task_id as optional. It does not name a sibling alternative (e.g. list_time_entries) for viewing existing entries, so it stops short of explicit when-not-to-use routing.

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