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

With no annotations provided, the description fully discloses behavioral quirks: tier caps on days, silent capping, the date parameter being ignored for non-enterprise tiers, and the return format (oldest first, includes tier_cap, effective_days, etc.). This goes beyond the schema and gives the agent critical runtime expectations.

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 dense but every sentence earns its place: purpose, usage triggers, required format, optional parameters, tier caps, a behavior caveat, and return structure. It's front-loaded with the core action and organized logically, with no fluff.

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 properly explains the return shape (array of daily snapshots, oldest first, plus metadata fields). It also covers the complex interplay of parameters (days vs date) and tier restrictions, making it complete for a 5-parameter tool with notable edge cases.

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?

Although the schema has 100% coverage, the description adds significant meaning beyond it: the mandatory '-USD' suffix for ticker, tier-capping behavior for days, and the enterprise-only honoring of the date anchor. These are not fully inferable from the schema alone and prevent costly mistakes.

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 starts with a specific verb and resource: 'Fetch a historical time series of daily snapshots for one crypto ticker.' It clearly distinguishes this from sibling tools like get_ticker_snapshot (current snapshot) and get_market_history (market-level history) by focusing on a single ticker's time series.

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 explicit when-to-use scenarios: 'Call this when the user asks about a ticker's recent trend, wants to chart or plot... asks how has X changed over the last N days, or needs a window of data.' It doesn't mention alternatives or when-not-to-use, but the context is clear. Without exclusions, 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.