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

Annotations already cover safety (readOnlyHint, openWorldHint), so the bar is lower, and the description still adds real context: a per-call cost of 1 credit, the exact shape of the returned data (per-day count, 0–4 intensity, annual total), and the either/or input constraint. It does not discuss pagination (presumably none, since one year), errors, or behavior when neither identifier is supplied.

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 short sentences: resource first, return shape second, cost and input rule last. Nothing is repeated from the title and every clause carries information.

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 carries the return-value burden and does so adequately by describing the calendar data and annual total. Combined with annotations covering safety and the schema covering most parameters, an agent has nearly everything needed; only cache_max_age and failure behavior are 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 75%, so the schema documents url, year (with default), and handle. The description adds the otherwise-implicit exclusivity rule that either handle or url must be passed, which is genuine semantic value beyond the schema. cache_max_age remains undocumented in both places, which keeps it from a 5.

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?

The description names a specific resource (contribution calendar for one calendar year) and specifies exactly what it returns: per-day count, GitHub's 0–4 intensity level, and the annual total. This is meaningfully more precise than the title alone. It stops short of naming a sibling such as github_activity or github_user to draw the boundary, so differentiation is implied rather than stated.

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?

"Pass either `handle` or `url`" gives a usable input-selection rule, but there is no explicit when-to-use versus github_activity or github_userRepositories, and no when-not guidance. Usage is implied by the resource description rather than stated.

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