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

Annotations already declare readOnly/openWorld/non-destructive, so the safety profile is covered. The description adds the OAuth scope requirement (read_heartbeats) and the exact REST endpoint, which is genuinely useful context not present in annotations or schema. Still silent on rate limits and pagination.

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 efficient sentences with the resource and returned fields front-loaded, followed by the auth requirement. The trailing GET /users/current/durations is largely redundant for an agent since the tool is already identified by name, but it costs little.

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 describing the returned item shape (start time, length, project/slice), and it covers the auth scope. An agent has enough to call it correctly; only edge behavior like result volume or pagination is unaddressed.

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% across all 7 parameters, including the enum for slice_by and per-field defaults, so the schema carries parameter meaning. The description's mention of 'project (or other slice)' loosely signals slice_by but adds no syntax or format detail beyond what the schema already states. Baseline 3 applies.

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 resource and scope: 'coding sessions (durations) of one day', and enumerates the returned fields (start time, length in seconds, project/slice). This clearly separates it from aggregate tools like get_summaries or get_stats, though it never names a sibling explicitly.

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?

Provides a real prerequisite ('Needs the read_heartbeats scope for OAuth tokens') and the underlying endpoint, which helps an agent predict behavior. However, it gives no guidance on when to pick this over get_heartbeats or get_summaries, so selection is left to inference.

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