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

With no annotations, the description carries the full burden and does so richly: exact auth header forms (Bearer adk_live_/adk_test_ or X-API-Key), the CONFLICTING_API_KEYS refusal when both are supplied, billing semantics (1000-bar slices rounded up, empty page free), the per-person minute ceiling tied to end_user_id, and that refusals map to /v1 codes.

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 core purpose is front-loaded and every clause carries information, but the auth and billing details make it a dense run-on that an agent must parse carefully. Nothing is wasted, yet the sentence structure could be tighter.

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 5-parameter read tool with no annotations and no output schema, the definition is nearly complete: it explains auth, pagination, limits, billing and error behavior. It stops short of describing the bar payload shape, though the pagination hint about next_before partially covers the return contract.

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 0%, so the description must compensate, and it does: it enumerates all timeframe values (D1..S1), bounds limit (1-5000), defines before as the prior response's next_before for reverse pagination, and explains end_user_id's role in rate limiting. Only symbol's syntax is left implicit, which is minor.

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 with scope and ordering: 'Candle history for one symbol, one page, oldest first.' The sibling tools (get_offer, list_symbols, quote_price_for) cover unrelated resources, so no sibling differentiation is needed, and the agent can tell exactly what this returns.

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?

Provides concrete usage mechanics: page backwards with 'before = the previous answer's next_before', and limit range 1-5000. It does not state when to prefer this over a sibling, but since the siblings are unrelated resources there is little ambiguity to resolve.

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