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

Annotations already declare readOnly, non-destructive, non-open-world, so the description need not re-state safety. It earns credit by disclosing output behavior the annotations don't: counts and aggregate specificity are returned rather than individual sites, and row cost scales with spacer count rather than site count. It adds no auth, rate-limit, or failure-mode context, so it stops short of a 5.

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 purpose and the workflow hook, then a value/scale rationale. The prose is dense with em-dashes but every clause contributes; no repetition or filler to trim beyond minor tightening.

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 9-parameter tool with an output schema and full annotation coverage, the description supplies what the structured fields cannot: the aggregate-vs-site distinction and the triage framing. Remaining parameter and return-format details are legitimately carried by the 100%-covered schema and output schema, so nothing essential is missing.

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 all nine parameters (spacers, subject, nuclease, bulges, max_mismatches, circular) are already documented in the schema at that baseline. The description's phrase 'by mismatch class' loosely gestures at max_mismatches but adds no syntax, defaults, or format meaning 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 and resource — counting every guide's off-target sites by mismatch class across one sequence — and immediately differentiates the tool's output scope from the per-guide site table ('never the sites themselves'). An agent can tell this apart from the site-listing sibling without opening a 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?

Frames the tool as 'the question that comes BEFORE opening any single guide's site table: which of these spacers is worth looking at', which is an explicit when-to-use signal tied to a triage workflow. It does not name the alternative tool (e.g. search_off_targets) or state exclusions, keeping it just short of fully explicit routing.

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