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

Annotations only declare readOnlyHint and openWorldHint, but the description adds substantial context beyond them: the cost profile ('makes 3 GitHub searches plus npm/PyPI lookups for the shortlist'), hosted rate limits (50 free calls/day), an auth requirement (X-GitHub-Token header for unlimited use), and a local fallback (npx -y whichlib). It also discloses the scoring model and tier thresholds so the agent can interpret output.

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-loaded with purpose and routing, then cost/auth details. It is dense and runs long for a single block, but nearly every clause carries decision-relevant information (routing, cost, auth, scoring, tier interpretation), so the length is largely earned rather than padding.

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 still covers the return shape (0-100 score with weighted sub-components, tier bands, one-line verdict, full breakdown) and the operational envelope (latency, rate limit, auth, local alternative). An agent has everything needed to call and interpret this tool.

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 documents need, limit and language with examples and constraints. The description adds the notion that results are ranked by fit = score x relevance and that limit caps returned repos, but no syntax or format detail beyond the schema. Baseline 3 applies when the schema carries the parameter burden.

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?

Opens with a specific verb+resource+outcome: 'Find the best open-source library for a need before adding a dependency.' It explicitly distinguishes itself from the sibling compare_repos ('use compare_repos when you already have names'), so an agent can route without opening either schema.

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?

Gives an explicit when-to-use ('when you do not yet have candidates') and the alternative with its trigger condition ('use compare_repos when you already have names'). The precondition of needing a plain-words need rather than a library name is also stated.

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