Prompt capture

v2.1.284 system prompt

SDK-CLI The system prompt of v2.1.284, as Agent SDK, print mode sent it to the model, read out of the request it put on the wire. The text comes first; what changed since the previous capture is further down, kept apart from it.

Released28 Sep 26captured 28 Sep 26

Compared withv2.1.283the previous capture taken the same way

Prompt218 ln27,201 characters

Model strings274 copies of the prompt between them

Tool descriptions24 9 moved this release, 23 with a parameter schema

Captured 6 ways. Each is a separate prompt with its own history, and a change is only ever measured against the previous capture taken the same way, never across these.

Default settings

Claude Code, interactive mode Agent SDK, print mode

a clean sandbox with no stored flags, as a fresh install runs

Seeded with feature flags

Claude Code, interactive mode, seeded with this account's feature flags Claude Code, interactive mode, seeded with anonymous feature flags Agent SDK, print mode, seeded with this account's feature flags Agent SDK, print mode, seeded with anonymous feature flags

the same client started with a stored set of feature flags on, so it can send text a default install does not. What that tells you

Read it The whole system prompt → 218 lines, 27,201 characters, with a reading view and a copy button

As plain textthe same prompt as a .txt, to download or diff
24 tool descriptionsthe text the model is given for each tool
11 appended blocks84,590 more characters the client sends after the system prompt
4 copies by modelthe prompt is not one text; which models get which copy
18 prompts in this releasecompaction, subagents, reminders: each its own request

What changed since the previous capture

11 One line per document that moved, the system prompt and the tool descriptions in the same table.

1 added and 1 removed, of 218 lines, about 4 words, in the prompt 15 of 27 arms receive. 3 other prompts also changed. 1 of 24 tool descriptions changed. The appended system-reminder blocks moved: 1 line added. Compared against v2.1.283.

The two arm counts on this page measure different things: 15 arms receive the prompt the headline is about, and the widest edit below reached 25, because the same changed lines sit in more than one prompt.

PromptReachMovedThe first line that changed

System prompt 218 ln, and 1 other copy of it moved the same way 25 of 27 arms +1−1 - The most recent Claude models are the Claude 5 family and Haiku 4.5. Model IDs — Fable 5.1: 'claude-fable-5-1', Opus 5.5: 'claude-opus-5-5', Sonnet...

System prompt, Sonnet 55 ln 2 of 27 arms +20−182 You are an interactive agent that helps users with software engineering tasks. Use the instructions below and the tools available to you to assist the...

Agent, Sonnet 15 ln 2 of 27 arms +7−68 ## When not to use

Bash, Sonnet 13 ln 2 of 27 arms +11−111 Executes a given bash command and returns its output.

Edit, Sonnet 5 ln 2 of 27 arms +4−8 Performs exact string replacements in files.

Read, Sonnet 9 ln 2 of 27 arms +5−11 Reads a file from the local filesystem. You can access any file directly by using this tool.

WebFetch, Sonnet 6 ln 2 of 27 arms +5−20 IMPORTANT: WebFetch WILL FAIL for authenticated or private URLs. Before using this tool, check if the URL points to an authenticated service (e.g. Goo...

WebSearch 27 ln 15 of 27 arms +1−1 - The current month is September 2026. You MUST use this year when searching for recent information, documentation, or current events.

WebSearch 5 ln 10 of 27 arms +1−1 - The current month is September 2026 — use this when searching for recent information.

WebSearch, Sonnet 5 ln 2 of 27 arms +4−26 Search the web. Returns result blocks with titles and URLs. US-only.

Write, Sonnet 3 ln 2 of 27 arms +2−7 Writes a file to the local filesystem.

The blocks the client appends after the system prompt moved as well, and this table does not cover them. The appended blocks, and which of them moved →

The prompt by model

4 The client does not send one system prompt: each model gets its own copy with its name and a few lines worked in. A row is one copy and how many of the 27 model strings get it, most first. Every copy opens with the same line: You are an interactive agent that helps users with software engineering tasks.

#CopyLengthSent toDocuments

1 Haiku, Sonnet and Opus, 15 model strings 218 ln · 27.2k 15 of 27 3 copies

2 Fable and Mythos, 2 model strings 78 ln · 9.9k 2 of 27 2 copies

3 Opus 5 family, 2 model strings 69 ln · 9k 2 of 27 1 copy

4 Opus and Sonnet, 8 model strings 55 ln · 5.6k 8 of 27 2 copies

Tool descriptions

24 The text the model is given for each tool, on this arm.

All 24 tool descriptions →

ToolDescriptionCopiesMoved

Agent 1,668 chars 3 ◆moved

Bash 1,229 chars 2 ◆moved

CronCreate 2,924 chars 1 ○same

CronDelete 167 chars 1 ○same

CronList 106 chars 1 ○same

Edit 360 chars 2 ◆moved

EnterWorktree 3,220 chars 1 ○same

ExitWorktree 1,923 chars 1 ○same

ListAgents 777 chars 1 ○same

NotebookEdit 619 chars 1 ○same

Read 790 chars 2 ◆moved

ReportFindings 574 chars 1 ○same

ScheduleWakeup 3,396 chars 1 ○same

SendMessage 4,259 chars 1 ○same

Skill 1,417 chars 1 ○same

TaskCreate 2,146 chars 1 ○same

TaskGet 732 chars 1 ○same

TaskList 998 chars 1 ○same

TaskStop 378 chars 1 ○same

TaskUpdate 2,243 chars 1 ○same

WebFetch 469 chars 2 ◆moved

WebSearch 334 chars 2 ◆moved

Workflow 3,480 chars 1 ○same

Write 240 chars 2 ◆moved