A guide for working with content identifiers (CIDs) used by the AT Protocol, a system for decentralized social apps. It covers handling these identifiers in Rust, TypeScript, and Go.

Use it to parse, create, check, verify, or debug CIDs for records, files, and commits in AT Protocol software.

It helps avoid incorrect CIDs by explaining the exact formats and validation rules expected by the protocol.

atproto-cid — Skill for Claude Code by ngerakines

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.

Any agent

npx skills add ngerakines/atproto-skills --skill atproto-cid

Clone the repo

git clone --depth 1 https://github.com/ngerakines/atproto-skills

Made for: Claude Code.

Or install atproto-skills, the plugin that ships this one along with the rest of its 7 skills.

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.

README.md

[![agentmods](https://agentmods.dev/badge/skills/ngerakines/atproto-skills/atproto-cid/github.svg)](https://agentmods.dev/skills/ngerakines/atproto-skills/atproto-cid)

Your own site

<a href="https://agentmods.dev/skills/ngerakines/atproto-skills/atproto-cid"><img src="https://agentmods.dev/badge/skills/ngerakines/atproto-skills/atproto-cid/github.svg" alt="Measured on agentmods" height="20"></a>

Or the 80×15 button, for a site that already has a row of RSS and ATOM ones. Only the verdict fits; the numbers stay here.

Your own site · 80×15

<a href="https://agentmods.dev/skills/ngerakines/atproto-skills/atproto-cid"><img src="https://agentmods.dev/badge/skills/ngerakines/atproto-skills/atproto-cid.svg" alt="Reviewed on agentmods" width="80" height="20"></a>

Per session 478 Skills are progressive disclosure: only the name and description are preloaded; the body loads when the skill is used.

When invoked 3,163 The whole file, excluding the scripts and references it only reads on demand.

Security scan A 0 findings. A grade says what 26 rules found in the file — not that it is safe.

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.

Model	Per session	Once invoked
Fable 5.1	$0.00478	$0.03163
Opus 5	$0.00239	$0.01581
Sonnet 5	$0.00096	$0.00633
Haiku 4.5	$0.00048	$0.00316

Measured 12d ago against content hash bc3231539692, method: parsed. Prices are Anthropic first-party input rates as of 2026-09-12, from the pricing page.

Security

Grade A, and why

atproto-cid 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 12d ago.

The scan reads SKILL.md. This mod also ships 1 executable file (scripts/validate_cid.py), listed below but not scanned — reading those needs a real analyzer, not pattern matching.

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.

skills/atproto-cid/SKILL.md · 168 lines

How it starts

The opening of the file, as written. The whole thing — 168 lines — stays where its author put it; the contents beside it link to each section on GitHub.

AT Protocol / DASL CIDs

Content Identifiers (CIDs) are the content-addressed hashes that bind every record, blob, and commit in AT Protocol to its exact bytes. This skill routes to per-language guides for Rust, TypeScript, and Go, sitting on top of a single language-neutral spec in shared/.

Defaults

A DASL CID is always a CIDv1 with codec raw (0x55) or dag-cbor (0x71), hash SHA-256 (0x12), 32-byte digest, base32lower string form with a leading b, 36-byte binary form. The BDASL extension permits BLAKE3 (0x1e) for large-file blobs. Anything outside that set is rejected — DASL is a strict subset of multiformats CIDs, not an alias.

Full normative rules: shared/spec.md. Byte-level diagrams: shared/binary-layout.md. Fixtures: shared/test-vectors.md. Cross-language differences: shared/divergence-matrix.md.

Language detection

Before generating or reviewing any CID code, determine the target language from project files or the file being edited:

Cargo.toml, *.rs, rust-toolchain.toml, any mention of atproto-dasl / cid / libipld → Rust — read from rust/.
package.json, tsconfig.json, *.ts, *.tsx, imports of multiformats / @ipld/dag-cbor → TypeScript — read from typescript/. Also *.js/*.jsx when there is no .ts present in the repo.
go.mod, *.go, imports of github.com/ipfs/go-cid → Go — read from go/.

Prefer the file being edited over the repo root when they disagree: a .ts client inside a Rust-workspace monorepo still means TypeScript for that task.

If multiple languages are present and the task does not point at one unambiguously, ask which one applies. Never mix CID libraries across languages in generated code.

If an unsupported language is detected (Python, Java, Elixir, Swift, …), point the user at shared/spec.md for the binary format and offer Rust as a reference implementation to transliterate from. Name this out explicitly — it converts a dead end into a partial success.

Read the full file on GitHub · 168 lines

Files

What ships with it

17 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.

12d ago First seen · 168 lines · 0 tokens per session scan A bc3231539692

Subscribe to this mod's changes

atproto-cid is a skill published in the GitHub repository ngerakines/atproto-skills (50 stars, last pushed 4mo ago), licensed MIT. It adds 478 tokens to every session and 3,163 once invoked, about $0.0024 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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