get_activity_histogram

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

Annotations already declare readOnlyHint=true and openWorldHint=false, and the description reinforces this with 'Read-only, one API call'. It adds genuinely useful non-obvious context: results are computed by Intervals.icu, pace/GAP buckets are speeds in m/s rendered as a pace range, and bucket_size only affects power and hr.

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 purpose in the first clause and follows with concrete examples, then output format. Slightly dense with parenthetical asides, but every sentence carries information and there is no filler.

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 describes the return shape (seconds and % per bucket) and the units for each metric. It also points to intervals://methods/comparisons for methodology. Complete enough to invoke correctly, though pagination/volume of buckets is not addressed.

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 enum values, defaults and bucket_size semantics are already documented in the schema. The description's restatement of units (W, bpm, m/s) and the bucket_size restriction largely duplicates it, adding no syntax or edge-case detail beyond the schema.

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+resource (time distribution of one activity) and immediately scopes it as 'independent of zone definitions', which cleanly distinguishes it from the sibling get_intensity_distribution. The concrete examples (polarisation, time above FTP, pace spread) pin down exactly what output to expect.

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?

'Use for...' gives a clear usage context and the 'independent of zone definitions' framing implies when this is preferable to zone-based siblings. However, it never explicitly names an alternative tool or states when NOT to use it, so the routing signal is implicit rather than spelled out.

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