devlog

A format and workflow for recording development work, decisions, discoveries, and future plans in dated Markdown files.

In plain words
What is it for?
It is for writing or updating concise devlog entries in a project’s devlog directory.
Why use it?
It preserves the reasoning behind changes so teammates can understand the project later.

Skill for Claude CodeCodex

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/block/trailblaze/devlog
Any agent
npx skills add block/trailblaze --skill devlog
Clone the repo
git clone --depth 1 https://github.com/block/trailblaze

Made for: Claude Code, Codex.

Per session 44 Skills are progressive disclosure: only the name and description are preloaded; the body loads when the skill is used.
When invoked 540 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 $0.00044 $0.00540
Opus 5 $0.00022 $0.00270
Sonnet 5 $0.00009 $0.00108
Haiku 4.5 $0.00004 $0.00054

Measured yesterday against content hash d96fe3a49bbc, method: parsed. Prices are Anthropic first-party input rates as of 2026-08-30, from the pricing page.

Security

Grade A, and why

devlog 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 yesterday.

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.

.claude/skills/devlog/SKILL.md · 68 lines

What it actually says

Devlog

Write or update a devlog entry in the devlog directory.

Devlog Format

Devlog entries are development journal posts that capture decisions, discoveries, and plans as work happens. They're written for the team — concise, honest, and useful for future reference.

Filename: YYYY-MM-DD-<topic-slug>.md

Use today's date and a short kebab-case topic slug.

Entry Structure

---
title: "Short Descriptive Title"
type: devlog
date: YYYY-MM-DD
---

# Title

## Summary
1-3 sentences on what this entry covers.

## <Sections as needed>
Use whatever sections make sense for the content. Common ones:
- What Changed
- Key Decisions (and rationale)
- What We Learned
- Open Questions
- Future Work

Keep it direct. No filler. Write like you're explaining to a teammate who will read this in 3 months.

Front Matter Fields

Field Required Values
title Yes Short descriptive title
type Yes decision (architectural/technical choice) or devlog (development note)
date Yes YYYY-MM-DD format

Use type: decision when recording a significant architectural or technical choice. Use type: devlog for development notes, debugging sessions, and implementation details.

Guidelines

  • Be opinionated. Capture why decisions were made, not just what happened.
  • Include the dead ends. What didn't work and why is often more valuable than what did.
  • Link to context. Reference PRs, branches, test names, file paths — make it traceable.
  • One entry per topic. Don't combine unrelated work. Multiple entries on the same day is fine.

Before Writing

  1. Check existing devlog entries to avoid duplicating a topic
  2. If updating an existing topic, consider appending to the existing entry rather than creating a new one
  3. Review the current conversation context for decisions, discoveries, and rationale worth capturing

Invocation

When the user says /devlog, ask what topic to write about if it's not clear from context. If you've been working on something substantial in the current session, suggest writing about that.

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. yesterday First seen · 68 lines · 44 tokens per session scan A d96fe3a49bbc

Subscribe to this mod's changes

devlog is a skill published in the GitHub repository block/trailblaze (303 stars, last pushed 6d ago), licensed Apache-2.0. It adds 44 tokens to every session and 540 once invoked, about $0.0002 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 2026-08-30.

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