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

Annotations already declare readOnlyHint=true, destructiveHint=false, openWorldHint=true, so safety is covered; the description adds genuinely new context: truncation behavior ('Large days are cut to `limit` heartbeats starting at `offset`'), the total_heartbeats count, and the required read_heartbeats scope. Return shape is only partially described, and pagination ordering is not explicit.

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?

Three sentences, front-loaded with the resource definition and ending with the endpoint and auth requirement. The middle sentence is dense with pagination facts, and the field enumeration in sentence one is list-like, but nothing is wasted.

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 usefully enumerates returned fields (entity, type, category, project, branch, language, time, lines, AI line changes) and covers pagination and auth. It is nearly complete for a single-parameter-required read tool, though it never states ordering of heartbeats or the concrete truncation default interaction.

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 explains date, limit (default 200) and offset (slice busy days, default 0). The description reinforces the limit/offset interplay but adds no format or constraint detail beyond the schema, so the baseline 3 is appropriate.

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?

Names a specific resource ('the raw heartbeats') and defines the jargon inline ('activity pings from editor plugins') of one day, then enumerates the fields returned. An agent can distinguish this from aggregate siblings like get_summaries, get_durations, and get_stats by the word 'raw' and the day scope.

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?

Usage is implied (fetch raw pings for a single day, slice busy days with limit/offset) and the OAuth prerequisite ('Needs the read_heartbeats scope for OAuth tokens') is stated, but there is no explicit when-to-use/when-not guidance relative to siblings such as get_durations for the same day.

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