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

With no annotations provided, the description carries the full burden of behavioral disclosure. It reveals important execution traits: a 2-credit cost, no charge for empty results or failures, default fresh fetch behavior, and the availability of a free cached response. The 'today grace' note hints at streak calculation nuance, though it is not fully explained.

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?

The description is compact and front-loaded with the core purpose. However, 'longestStreak (2 credits)' followed by 'Costs 2 credits' creates minor ambiguity about whether the 2 credits refers to the longestStreak field or the entire call, which costs a little clarity.

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 simple two-parameter tool, the description covers the essential operational context: cost, caching, failure charging policy, and a rough sketch of the return shape. It does not explicitly route the agent to a sibling for profile data or describe all output details in the absence of an output schema, but the needed info for a correct call is 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%, so the baseline is 3. The description reiterates the cache parameter's behavior ('cache=true for a free 24h cache hit') and mentions username indirectly through the tool's purpose, but it does not add meaningful detail beyond what the input schema already documents.

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 opens with a specific noun phrase 'GitHub contribution graph' and enumerates the output fields (sorted days[], currentStreak, longestStreak), making it clear this is about contribution history statistics. This distinguishes it from sibling tools like github_user, github_repositories, or github_activity, even without naming 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?

The description gives actionable usage guidance about cost and caching: using cache=true for a free 24-hour hit, and noting that empty results/failures are never charged. It does not explicitly compare to alternative GitHub tools or state when not to use it, so it misses the top score but provides clear operational context.

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