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

Annotations already declare readOnlyHint=true and destructiveHint=false, but the description adds substantial behavioral nuance: open vs Pro mode with different result limits (5 vs 10, capped at 200 or 10), seeMoreOnSite pointing to the comparer, detailUrl using MCP.public_base_url, and a disclaimer that data is indicative and may change. This goes well beyond the structured annotations and gives the agent a clear picture of what to expect.

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 longer than two sentences but is well-structured: main purpose, mode behavior, usage guidance, data disclaimer, and English keywords. Every section adds value, though the English keyword list could be trimmed for brevity. It is front-loaded with the core action and maintains clarity throughout.

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 no output schema, the description carries the responsibility of explaining behavior. It covers result limits, URL construction, data reliability, and provides detailed usage scenarios. For a read-only tool with four optional filters, this description is thoroughly complete, leaving little ambiguity for an agent.

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 enriches parameter meaning by explaining how 'limit' behaves differently in open vs Pro modes (teto 200 or 10), and it lists the filter dimensions (tipo, distribuidor, prazo, limite) in the opening line. This extra context about parameter constraints and usage justifies a score above baseline.

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 'Busca as melhores oportunidades de renda fixa disponíveis na Meelion', a specific verb (busca) combined with a clear resource (melhores oportunidades de renda fixa). It also lists concrete examples like CDB, LCI, LCA, CRI, CRA, and debêntures, which clearly distinguishes it from sibling tools focused on indicators, projections, details, or quotes. The purpose is unmistakable.

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 explicitly states when to use the tool ('Use quando o usuário quiser encontrar onde o dinheiro pode render mais, comparar... ver rankings...'), providing clear use cases. However, it does not mention when not to use it or reference alternative sibling tools, so it falls short of the highest bar for explicit exclusions/alternatives.

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