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

Annotations already declare readOnly/idempotent/non-destructive, so the safety burden is carried. The description still adds real behavioral context beyond them: it discloses the two upstream data sources, the AR vs GETS value semantics, and that mode (c) returns a bounded top-25-per-side summary. It doesn't discuss recency or coverage gaps of the sources.

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 the core concept, then structured into sources, modes, use cases, and value legend. Roughly 110 words that each carry distinct information; no filler or redundancy.

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 an output schema present, return-value documentation is unnecessary and the description correctly focuses on inputs, sourcing, and mode behavior. For a zero-required-parameter lookup tool, an agent has everything needed to call it correctly.

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, and the description earns above it by explaining what each parameter selects (agency→charities, charity→agencies, neither→platform summary) and illustrating accepted slug/name formats. It doesn't restate the limit default beyond what the 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?

States a specific verb+resource ('agency↔charity funding graph') and decomposes it into two named data sources and three call modes. An agent can determine exactly what this returns without opening the schema. This meaningfully distinguishes it from generic siblings like get_government_contracts or get_corporate_giving.

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 three modes (a/b/c) give explicit when-to-use conditions keyed to which parameter is passed, and the example questions ('which charities does MSD fund', 'who funds Women's Refuge') anchor intent. It lacks explicit exclusions or named alternative siblings, so it falls short of a 5.

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