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

With no annotations, the description carries the full burden; it does disclose the returned data shape (per-day contributions with GitHub quartile level, totals, streaks, busiest month) and the accompanying Byteland image. It says nothing about auth requirements, rate limits, or what happens for invalid handles or future years, so the behavioral picture is partial.

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 sentences, front-loaded with the core purpose; the colon-list of returned metrics is dense but scannable. The trailing parenthetical about twelve month buildings is slightly ornamental but still informative.

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?

For a two-parameter, read-only style lookup with no output schema, the description enumerates the return contents well enough to set expectations. The one gap is how the image is delivered (URL vs. inline payload) and whether it is always present.

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% and both parameters are documented in-schema, so the baseline is 3. The description reinforces the 'one year' and 'anyone's handle' framing but adds no syntax or format 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 concrete verb+resource: a GitHub contribution calendar for one year, broken down by month, with named aggregates. It is distinguishable from siblings like get_stats or get_profile by its per-day/per-month calendar scope, though it never explicitly contrasts itself with them.

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 by the resource description (fetch someone's yearly contribution calendar), but there is no explicit when-to-use/when-not guidance and no mention of when get_stats or get_profile would be the better pick.

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