tech-plan

tech-plan is a skill for Claude Code, Codex from blake-simpson/belmont. It costs 14 tokens per session (10,418 once invoked), scanned A, original, Apache-2.0.

A planning guide that turns a product requirements document, or PRD, into a detailed technical implementation plan. A PRD describes what a product should do; the plan describes how to build it.

In plain words
What is it for?
Creating TECH_PLAN.md files, reviewing architecture trade-offs, mapping dependencies, and keeping the plan aligned with the PRD and project progress.
Why use it?
It separates design decisions from coding, helping teams agree on architecture, dependencies, and milestones before implementation begins.

Skill for Claude CodeCodex

Part of the belmont plugin — 17 skills, 6 agents shipped together

Install

Getting it into your agent

One page per mod, every tool's command on it. A separate URL per tool would split the same page into five that compete with each other.

agentmods
npx agentmods add skills/blake-simpson/belmont/tech-plan
Any agent
npx skills add blake-simpson/belmont --skill tech-plan
Clone the repo
git clone --depth 1 https://github.com/blake-simpson/belmont

Made for: Claude Code, Codex.

Or install belmont, the plugin that ships this one along with the rest of its 17 skills, 6 agents.

Wrote this? Show the measurements

A badge with what this costs and how it scanned, read live from this page, so it follows the numbers instead of freezing them. Markdown for a README, HTML for a documentation site or a project page.

agentmods badge for tech-plan

README.md
[![agentmods](https://agentmods.dev/badge/skills/blake-simpson/belmont/tech-plan.svg)](https://agentmods.dev/skills/blake-simpson/belmont/tech-plan)
Your own site
<a href="https://agentmods.dev/skills/blake-simpson/belmont/tech-plan"><img src="https://agentmods.dev/badge/skills/blake-simpson/belmont/tech-plan.svg" alt="Measured on agentmods" height="20"></a>
Per session 14 Skills are progressive disclosure: only the name and description are preloaded; the body loads when the skill is used.
When invoked 10,418 The whole file, excluding the scripts and references it only reads on demand.
Security scan A 0 findings. Scan, not verified.
Origin original No closer match found in the catalogue.
Token cost

What it costs to keep this loaded

Counted locally with the o200k_base tokenizer, which is exact for GPT models; Claude uses its own tokenizer and its counts differ. Treat this as one consistent yardstick across the catalogue rather than a bill. Prices are per million input tokens.

ModelPer sessionOnce invoked
Fable 5 $0.00014 $0.10418
Opus 5 $0.00007 $0.05209
Sonnet 5 $0.00003 $0.02084
Haiku 4.5 $0.00001 $0.01042

Measured 4d ago against content hash 1460611cfe61, method: parsed. Prices are Anthropic first-party input rates as of 2026-08-30, from the pricing page.

Security

Grade A, and why

tech-plan scanned grade A with 0 findings against 26 rules in 11 categories — prompt injection, anti-refusal, data exfiltration, privilege escalation, supply chain, agent snooping, system-prompt leakage, SSRF and excessive agency — measured 4d ago.

A static scan of the body, not an audit. Every finding is printed with the line that produced it so you can judge whether it matters here. A mod is markdown that instructs an agent; that is exactly why what it instructs is worth reading.

Nothing flagged

None of the 26 patterns this scan looks for appear in this file: no shell pipes, no recursive deletes, no credential paths, no hidden text, no instruction-override or anti-refusal phrasing, no agent-config snooping. That is not a guarantee, it is the absence of the things that are checkable.

plugin/skills/tech-plan/SKILL.md · 587 lines

How it starts

The opening of the file, as written. The whole thing — 587 lines — stays where its author put it; the contents beside it link to each section on GitHub.

Belmont: Tech Plan

You are a senior software architect creating a detailed implementation specification. Your goal is to produce a TECH_PLAN.md together with the human user so that the human user is 100% confident in the plan.

This session requires ultrathink-level reasoning — deeply analyze architecture trade-offs, dependency chains, and cross-cutting concerns before proposing implementation approaches.

CRITICAL RULES

  1. This is ONLY a planning session. Do NOT implement anything.
  2. Do NOT create or edit any source code files (no .tsx, .ts, .css, etc.).
  3. When done asking questions, write plan(s) to the appropriate TECH_PLAN.md file(s) (see routing logic below).
  4. Reconcile the PRD and PROGRESS with every decision made this session — including contradictions, refinements, leaked tech detail, and dependency annotations. See the "Tech-plan's Back-update Contract" section of the plan-separation partial below. This is not optional; skipping it is the #1 cause of implementation drift.
  5. Respect milestone sizing rules — see the plan-separation partial. If a newly-discovered task represents genuinely new feature work (a vertical slice the user didn't originally plan), default to creating a NEW small milestone rather than inflating an existing one. This preference does NOT apply to follow-ups, polish, or fixes surfaced by implement/verify cycles — those always go back to the milestone that discovered them. See the milestone-immutability partial (included below) for the full rule.
  6. After writing the tech plan AND completing Phase 4.5 (PRD Reconciliation), say "Tech plan complete." and STOP.

Codex Plan-Mode Preflight

Codex exposes keyboard-navigable structured questions through plan-mode planning turns. If you are Codex and the structured question tool is unavailable in the current turn, STOP before asking any technical planning questions or editing files. Tell the user to restart this skill with:

/plan $belmont:tech-plan <feature or brief>

Read the full file on GitHub · 587 lines

Files

What ships with it

3 files beside SKILL.md in the same directory: the scripts, references and assets a skill reads on demand. Not counted in the per-session cost; read them before you install if any of them is executable.

Changes

What this file has done since we first saw it

Hashed on every crawl. A supply-chain change to an agent config is a question of when, not whether, so the history is kept rather than the latest state alone.

  1. 4d ago First seen · 587 lines · 14 tokens per session scan A 1460611cfe61

Subscribe to this mod's changes

tech-plan is a skill published in the GitHub repository blake-simpson/belmont (4 stars, last pushed 16d ago), licensed Apache-2.0. It adds 14 tokens to every session and 10,418 once invoked, about $0.0001 per session on Opus 5. A static security scan graded it A with 0 findings. No closer match exists in the catalogue, so it is treated as the original; first seen 2026-08-31.