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chrome_page_load_script_hotspots

Read-onlyIdempotent

Identifies and ranks script groups on the renderer main thread during Chrome page loads, showing wall time, CPU time, and style/layout contributions to diagnose slow First Contentful Paint or load events.

Instructions

Rank renderer main-thread script groups in a Chrome page-load/raw window: URL/name/process/thread, wall/CPU totals, style/layout ms, example_slice_id. Read-only.

Use when: slow FCP/load needs post-resource JS attribution; expand example_slice_id with slice_descendants_breakdown.

Parameters: optional process filters, page-load/window filters shared with chrome_main_thread_hotspots, min_total_ms (default 20), limit, max_string_len. Empty result: no matching script groups.

Input Schema

TableJSON Schema
NameRequiredDescriptionDefault
end_ts_nsNoOptional raw trace timestamp upper bound in nanoseconds, exclusive. This uses the same unit as trace `slice.ts`. ANDs with any page-load window.
limitNoOptional max rows to return. Defaults to 100 and is capped at 5000. Must be > 0 when set.
max_string_lenNoOptional per-string-cell character cap applied to returned rows only. Unset preserves full strings for precision; accepts both numbers and numeric strings. Must be > 0 when set.
min_total_msNoOptional minimum aggregated wall time per grouped script hotspot. Defaults to 20 ms. Pass 0 to see every matching group.
navigation_idNoOptional Chrome navigation id used to scope scripts to one navigation phase. Matches `chrome_page_loads.navigation_id`. Mutually exclusive with `page_load_id`. If set without `phase`, defaults to `navigation_to_fcp`.
page_load_idNoOptional page-load id used to scope scripts to one navigation phase. Matches `chrome_page_loads.id`. Mutually exclusive with `navigation_id`. If set without `phase`, defaults to `navigation_to_fcp`.
phaseNoOptional page-load phase window. If set without `page_load_id` or `navigation_id`, uses the latest page load in the trace. Values: navigation_to_fcp, navigation_to_load, dcl_to_fcp, fcp_to_load.
pidNoOptional OS pid filter. Accepts both numbers and numeric strings.
process_nameNoOptional process-name filter (e.g. "Renderer"). Useful to scope one process type without picking a specific instance.
start_ts_nsNoOptional raw trace timestamp lower bound in nanoseconds. This uses the same unit as trace `slice.ts`. ANDs with any page-load window.
upidNoOptional trace-internal upid filter. Prefer this when distinguishing same-named Renderer processes. Accepts numbers and numeric strings.

Tool Definition Quality

A4.5/5.0
Behavior4/5

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

Annotations already provide readOnlyHint, destructiveHint, idempotentHint, and openWorldHint. The description adds context about ranking behavior, output fields, and empty result meaning. No contradictions with annotations.

Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.

Conciseness5/5

Is the description appropriately sized, front-loaded, and free of redundancy?

The description is three sentences: purpose and output, usage guideline, parameter summary. It is front-loaded and contains no redundant information.

Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.

Completeness5/5

Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?

Given 11 parameters all described in the schema, and no output schema, the description covers output fields, parameter roles, and result interpretation (empty result means no matching groups). It is complete for a data retrieval tool.

Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.

Parameters4/5

Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?

With 100% schema description coverage, the baseline is 3. The description adds value by grouping parameters (process filters, page-load/window filters, limit, etc.) and highlighting the default min_total_ms of 20 ms.

Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.

Purpose5/5

Does the description clearly state what the tool does and how it differs from similar tools?

The description clearly states it ranks renderer main-thread script groups, lists output fields (URL/name/process/thread, wall/CPU totals, style/layout ms, example_slice_id), and indicates it is read-only. This differentiates it from the general main-thread hotspots sibling tool.

Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.

Usage Guidelines4/5

Does the description explain when to use this tool, when not to, or what alternatives exist?

Explicitly states when to use (slow FCP/load needing JS attribution) and recommends expanding with a follow-up tool. However, it does not specify when not to use or compare to other sibling tools like chrome_main_thread_hotspots.

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

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