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

Annotations already cover the safety profile (readOnlyHint, destructiveHint=false, openWorldHint), so the bar is lower, and the description still adds real value: exact image contents, the exclusion of indicators, and a freshness guarantee ('updated every minute'). It doesn't state latency, size limits, or whether a failed symbol returns an error versus an empty image, which keeps it below a 5.

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?

Two compact sentences, front-loaded with the core purpose, followed by contents and update cadence. The trailing copyright sentence ('The image is © TraderWAI') is arguably attribution boilerplate rather than invocation guidance, so it is the one part that doesn't clearly earn its place.

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 correctly informs the agent that the return value is an image, not structured data — a critical and non-obvious detail — and adds content and freshness context. Missing only failure behavior and whether any rate/quota applies to a repeatedly-refreshed image endpoint.

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% and both parameters are documented with concrete examples (EUR_USD, M1/M5/H1/D), so the schema carries the semantic load. The description only restates 'for a symbol and timeframe' and adds no format or validity constraints beyond that; baseline 3 applies.

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 ('Returns a candlestick chart image for a symbol and timeframe') and enumerates the visual contents (candles, day/session separators, last price). The clause 'without indicators' implicitly distinguishes it from the indicator-capable draw_chart sibling, but never names that sibling, so the differentiation is inferential rather than explicit.

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?

Usage context is only implied: an agent can infer it should call this when it needs a visual chart rather than raw candles (get_ohlc) or an annotated drawing (draw_chart). There is no explicit 'use this instead of X' statement and no stated preconditions such as needing a valid symbol from list_symbols.

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