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

Annotations already declare readOnly/idempotent/non-destructive, so safety is covered. The description adds genuinely new behavioral context: free vs 'Attic Standard MCP PRO' tier gating, the 260-week cap, and the unit convention ('per 1,000 tokens; other modalities use their own unit'). That is useful beyond the annotations, though it still doesn't describe pagination or ordering.

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?

It is front-loaded with the two modes, then the unit caveat, then examples – a sensible priority order with no filler sentences. It runs slightly long with the examples, but every part is load-bearing for correct invocation.

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 carries the return-shape burden and does so: index mode returns benchmark level, May 2026 = 100, and spot price with 25th/75th percentiles; model mode returns per-vendor weekly prices and repricing events. Combined with the tier and unit notes, 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 description coverage is 100%, so the baseline is 3, but the description adds real semantic value: it explains that index_code is free while model_name and vendor are PRO, and clarifies that vendor only applies 'with model_name'. The per-token/per-unit note further disambiguates the prices being returned.

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?

It names a specific verb and resource ('Weekly history') and splits the tool into two clearly scoped modes driven by index_code vs model_name, so the agent knows exactly what gets returned in each case. It does not, however, explicitly contrast itself with siblings like compare_prices or get_index_benchmarks, which is what separates a 5 from a 4.

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 two worked examples ('How has the neocloud index moved since May?' -> index_code='NCL'; 'Has anyone cut the price of DeepSeek V3 this quarter?' -> model_name=..., weeks=13) effectively show when to pick each mode. There is no explicit when-not guidance or named alternative tool, so it stops 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.