Sequential Thinking Skill

Purpose

Give Claude structured, iterative reasoning during analysis-heavy phases. Rather than jumping to conclusions, Claude builds a chain of connected thoughts — revising earlier ones when new evidence emerges, branching when multiple paths exist — before writing output or spawning a sub-agent.

This improves the quality of:

• Root-cause hypotheses in /fw:debug
• Architecture decisions in /fw:design and /fw:implement
• Threat modeling in /fw:harden
• ADRs produced by the fw-architect persona

Prerequisite: The sequential-thinking MCP server must be installed. Run /fw:setup for detection and installation guidance.

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Trigger Conditions

This skill activates automatically based on the complexity tier already detected in Step 0 of each command. No new detection logic is needed.

Tier	Signal words / conditions	Activation
light / small / low	config, style, typo, rename, simple addition	❌ Skip — fast path, no overhead
standard / medium	new feature, integration, refactor, runtime error	✅ Activate
deep / large / critical	architecture, migration, crash, security, system redesign	✅ Always activate

For /fw:harden (which uses scope rather than severity): skip for file scope; activate for module, project, and branch scope.

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MCP Call Pattern

Invoke the tool in a reasoning loop:

mcp__sequential-thinking__sequentialthinking({
  thought: "<current reasoning step — one focused idea>",
  thoughtNumber: <N, starting at 1>,
  totalThoughts: <estimated count, adjustable as reasoning progresses>,
  nextThoughtNeeded: <true to continue, false when done>
})

Optional — revise an earlier thought when new evidence invalidates a prior conclusion:

  isRevision: true,
  revisesThought: <thought number being corrected>

Optional — branch when two paths warrant parallel exploration:

  branchFromThought: <thought number to branch from>,
  branchId: "<descriptive branch name>"

Reasoning loop

1. Start with thoughtNumber: 1 — frame the core question or constraint
2. Each subsequent thought builds on, refines, or challenges the previous
3. Adjust totalThoughts freely as understanding grows
4. Set nextThoughtNeeded: false on the final thought
5. Hard cap: 8 thoughts per phase — if reached, treat as complete

Starter thought templates

Context	Thought 1 starter
/fw:debug Phase 2	"What is the core failure, and at which layer of the call chain does it occur?"
/fw:design Phase 3	"What are the fundamental design constraints and trade-offs for this goal?"
/fw:implement Phase 2	"What are the key integration risks and dependencies for this feature?"
/fw:harden Phase 1	"What are the primary attack surfaces and trust boundaries in this scope?"
fw-architect ADR	"What existing patterns in this codebase should govern this architecture decision?"

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Integration Pattern

Sequential thinking runs before spawning sub-agents or writing structured output. It is a Claude-native MCP call — it cannot be used inside dispatch.sh sub-agents.

Command Phase (standard/medium/deep/large/critical)
    │
    ├─ [Sequential thinking skill]
    │   ├─ thought 1: frame the problem
    │   ├─ thought 2–N: explore, revise, branch as needed
    │   └─ nextThoughtNeeded: false → reasoning complete
    │
    ├─ Sequential Analysis Summary (2-4 sentences)
    │   └─ Injected into sub-agent context as SEQUENTIAL ANALYSIS:
    │
    └─ Spawn sub-agent / write output
         └─ Richer output built on structured prior reasoning

Output: Sequential Analysis Summary

After the loop ends, synthesise the reasoning into a Sequential Analysis Summary — 2-4 sentences capturing:

• The core insight or problem framing
• Key unknowns or risks identified during reasoning
• The recommended focus for the next phase

Include this summary in the sub-agent task prompt under the heading SEQUENTIAL ANALYSIS:.

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Error Handling

Every failure is non-blocking. This skill is purely additive.

Failure	Behaviour
mcp__sequential-thinking__sequentialthinking unavailable	Skip the entire block silently; proceed to sub-agent or output
Tool returns error mid-loop	Stop loop; synthesise from thoughts completed so far
Hard cap of 8 thoughts reached	Treat as complete; synthesise immediately
Reasoning becomes circular	Detect repeated content → set nextThoughtNeeded: false

When skipped entirely, no note is added to output. The phase proceeds as if the skill does not exist.

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Token Budget

• Max 8 thoughts per phase — most problems resolve in 4–6
• One focused idea per thought — not a wall of text
• The Sequential Analysis Summary (2-4 sentences) is what gets injected downstream, not the raw thought log
• Skip entirely if the task is unambiguous and the answer is already evident from the Phase 1 codebase scan

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Installation

The sequential-thinking MCP server must be installed. Run /fw:setup — it will detect availability and print the install command if missing:

claude mcp add sequential-thinking npx @modelcontextprotocol/server-sequential-thinking