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

Annotations already declare readOnlyHint=true, so the safety profile is covered. The description adds a genuinely behavioral prerequisite the schema never states — that at least one filter must be supplied — and notes running_only surfaces timers with no end_time, but says nothing about truncation behavior (left to the schema) or auth requirements.

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?

Four dense sentences, front-loaded with the resource and its return shape, then constraints, then the upstream endpoint. Nothing is padding; even the Paymo endpoint pointer earns its place as an escape hatch for edge-case filtering.

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 compensates by listing returned fields, and it covers the mandatory-filter rule that governs 11 optional parameters. Combined with 100% schema coverage on the parameters themselves, an agent has everything needed to call this correctly.

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 100%, so the baseline is 3, but the description contributes a cross-parameter constraint not expressible in the schema (at least one filter required) and clarifies that from/to filter on the entry's own interval and that running_only selects entries lacking an end_time.

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 (List) and resource (time entries), and enumerates the returned fields, which lets an agent distinguish it from the other list_* siblings (tasks, projects, invoices) without ambiguity. It stops short of naming a sibling to use instead, but the resource is unique among siblings so differentiation is effectively achieved by the noun.

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?

"At least one filter is required" and the from/to and running_only semantics give concrete conditions for correct invocation. It does not, however, name an alternative tool or an exclusion case (e.g., use start_timer for the running-timer lifecycle), so it stays a clear-context-4 rather than a full routing statement.

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