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

Annotations already declare readOnlyHint, idempotentHint, and destructiveHint. The description adds valuable behavior beyond that: it never raises a protocol error and instead returns an error object, and it explicitly says retrying is safe after correcting input. This goes beyond the annotations without contradicting them.

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 front-loaded with the core purpose and includes a compact example, dynamic resource explanation, use cases, exclusions, and error behavior. Each section earns its place, though 'FREE.' is a minor digression and the overall text is slightly longer than strictly necessary.

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?

Given the tool's flexible additionalProperties schema, the description covers the key invocation details: constrained resources, multiplicity via qty, error behavior, retry safety, and appropriate use cases. The output schema exists, so the return structure in the example and solver_status is sufficient for an agent to understand what to expect.

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 baseline is 3. The description adds meaningful semantic detail beyond the schema by explaining that any numeric item field named in limits becomes a constrained resource and that qty allows an item to be taken multiple times. The worked example further clarifies how items and limits map to the selected output.

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 first sentence states a specific verb and resource: 'Choose the items that maximise value under one or more capacity limits.' It clearly identifies the knapsack problem and distinguishes it from sibling tools by saying it is for budgets, cargo, campaign, or feature selection and not for dependencies between items.

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 explicit use cases ('Use for budgets, cargo, campaign or feature selection') and an explicit exclusion ('Not for dependencies between items'), but it does not name an alternative sibling tool. This is clear context without fully specifying what to use instead when dependencies exist.

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